Add mcutie MQTT client implementation and improve library structure

- Integrated `mcutie` library as a core MQTT client for device communication.
- Added support for Home Assistant entities (binary sensor, button) via MQTT.
- Implemented buffer management, async operations, and packet encoding/decoding.
- Introduced structured error handling and device registration features.
- Updated `Cargo.toml` with new dependencies and enabled feature flags for `serde` and `log`.
- Enhanced logging macros with configurable options (`defmt` or `log`).
- Organized codebase into modules (buffer, components, IO, publish, etc.) for better maintainability.

Software/MainBoard/rust/src/mcutie_3_0_0/Cargo.toml

@@ -0,0 +1,34 @@
+[package]
+name = "mcutie"
+version = "3.0.0"
+edition = "2021"
+
+[lib]
+path = "lib.rs"
+
+[features]
+default = []
+homeassistant = []
+serde = ["dep:serde", "heapless/serde"]
+defmt = []
+log = ["dep:log"]
+
+[dependencies]
+embassy-net = { version = "0.8.0", default-features = false, features = ["tcp", "dns", "proto-ipv4", "proto-ipv6", "medium-ethernet"] }
+embassy-sync = { version = "0.8.0", default-features = false }
+embassy-time = { version = "0.5.1", default-features = false }
+embassy-futures = { version = "0.1.2", default-features = false }
+embedded-io = { version = "0.7.1", default-features = false }
+embedded-io-async = { version = "0.7.0", default-features = false }
+heapless = { version = "0.7.17", default-features = false }
+mqttrs = { version = "0.4.1", default-features = false }
+once_cell = { version = "1.21.3", default-features = false, features = ["critical-section"] }
+pin-project = { version = "1.1.10", default-features = false }
+hex = { version = "0.4.3", default-features = false }
+serde = { version = "1.0.228", default-features = false, features = ["derive"], optional = true }
+log = { version = "0.4.28", default-features = false, optional = true }
+
+[dev-dependencies]
+futures-executor = "0.3.31"
+futures-timer = "3.0.3"
+futures-util = "0.3.31"

Software/MainBoard/rust/src/mcutie_3_0_0/buffer.rs

@@ -0,0 +1,124 @@
+use core::{cmp, fmt, ops::Deref};
+
+use embedded_io::{SliceWriteError, Write};
+use mqttrs::{encode_slice, Packet};
+
+use crate::Error;
+
+/// A stack allocated buffer that can be written to and then read back from.
+/// Dereferencing as a [`u8`] slice allows access to previously written data.
+///
+/// Can be written to with [`write!`] and supports [`embedded_io::Write`] and
+/// [`embedded_io_async::Write`].
+pub struct Buffer<const N: usize> {
+    bytes: [u8; N],
+    cursor: usize,
+}
+
+impl<const N: usize> Default for Buffer<N> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<const N: usize> Buffer<N> {
+    /// Creates a new buffer.
+    pub(crate) const fn new() -> Self {
+        Self {
+            bytes: [0; N],
+            cursor: 0,
+        }
+    }
+
+    /// Creates a new buffer and writes the given data into it.
+    pub(crate) fn from(buf: &[u8]) -> Result<Self, Error> {
+        let mut buffer = Self::new();
+        match buffer.write_all(buf) {
+            Ok(()) => Ok(buffer),
+            Err(_) => Err(Error::TooLarge),
+        }
+    }
+
+    pub(crate) fn encode_packet(&mut self, packet: &Packet<'_>) -> Result<(), mqttrs::Error> {
+        let len = encode_slice(packet, &mut self.bytes[self.cursor..])?;
+        self.cursor += len;
+
+        Ok(())
+    }
+
+    #[cfg(feature = "serde")]
+    /// Serializes a value into this buffer using JSON.
+    pub(crate) fn serialize_json<T: serde::Serialize>(
+        &mut self,
+        value: &T,
+    ) -> Result<(), serde_json_core::ser::Error> {
+        let len = serde_json_core::to_slice(value, &mut self.bytes[self.cursor..])?;
+        self.cursor += len;
+
+        Ok(())
+    }
+
+    #[cfg(feature = "serde")]
+    /// Deserializes this buffer using JSON into the given type.
+    pub fn deserialize_json<'a, T: serde::Deserialize<'a>>(
+        &'a self,
+    ) -> Result<T, serde_json_core::de::Error> {
+        let (result, _) = serde_json_core::from_slice(self)?;
+
+        Ok(result)
+    }
+
+    /// The number of bytes available for writing into this buffer.
+    pub fn available(&self) -> usize {
+        N - self.cursor
+    }
+}
+
+impl<const N: usize> Deref for Buffer<N> {
+    type Target = [u8];
+
+    fn deref(&self) -> &Self::Target {
+        &self.bytes[0..self.cursor]
+    }
+}
+
+impl<const N: usize> fmt::Write for Buffer<N> {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        self.write_all(s.as_bytes()).map_err(|_| fmt::Error)
+    }
+}
+
+impl<const N: usize> embedded_io::ErrorType for Buffer<N> {
+    type Error = SliceWriteError;
+}
+
+impl<const N: usize> embedded_io::Write for Buffer<N> {
+    fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error> {
+        if buf.is_empty() {
+            return Ok(0);
+        }
+
+        let writable = cmp::min(self.available(), buf.len());
+        if writable == 0 {
+            Err(SliceWriteError::Full)
+        } else {
+            self.bytes[self.cursor..self.cursor + writable].copy_from_slice(buf);
+            self.cursor += writable;
+            Ok(writable)
+        }
+    }
+
+    fn flush(&mut self) -> Result<(), Self::Error> {
+        Ok(())
+    }
+}
+
+impl<const N: usize> embedded_io_async::Write for Buffer<N> {
+    async fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error> {
+        <Self as embedded_io::Write>::write(self, buf)
+    }
+
+    async fn flush(&mut self) -> Result<(), Self::Error> {
+        Ok(())
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/fmt.rs

@@ -0,0 +1,80 @@
+#![macro_use]
+
+#[cfg(all(feature = "defmt", feature = "log"))]
+compile_error!("The `defmt` and `log` features cannot both be enabled at the same time.");
+
+#[cfg(not(feature = "defmt"))]
+use core::fmt;
+
+#[cfg(feature = "defmt")]
+pub(crate) use ::defmt::Debug2Format;
+
+#[cfg(not(feature = "defmt"))]
+pub(crate) struct Debug2Format<D: fmt::Debug>(pub(crate) D);
+
+#[cfg(feature = "log")]
+impl<D: fmt::Debug> fmt::Debug for Debug2Format<D> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+#[collapse_debuginfo(yes)]
+macro_rules! trace {
+    ($s:literal $(, $x:expr)* $(,)?) => {
+        #[cfg(feature = "defmt")]
+        ::defmt::trace!($s $(, $x)*);
+        #[cfg(feature = "log")]
+        ::log::trace!($s $(, $x)*);
+        #[cfg(not(any(feature="defmt", feature="log")))]
+        let _ = ($( & $x ),*);
+    };
+}
+
+#[collapse_debuginfo(yes)]
+macro_rules! debug {
+    ($s:literal $(, $x:expr)* $(,)?) => {
+        #[cfg(feature = "defmt")]
+        ::defmt::debug!($s $(, $x)*);
+        #[cfg(feature = "log")]
+        ::log::debug!($s $(, $x)*);
+        #[cfg(not(any(feature="defmt", feature="log")))]
+        let _ = ($( & $x ),*);
+    };
+}
+
+#[collapse_debuginfo(yes)]
+macro_rules! info {
+    ($s:literal $(, $x:expr)* $(,)?) => {
+        #[cfg(feature = "defmt")]
+        ::defmt::info!($s $(, $x)*);
+        #[cfg(feature = "log")]
+        ::log::info!($s $(, $x)*);
+        #[cfg(not(any(feature="defmt", feature="log")))]
+        let _ = ($( & $x ),*);
+    };
+}
+
+#[collapse_debuginfo(yes)]
+macro_rules! warn {
+    ($s:literal $(, $x:expr)* $(,)?) => {
+        #[cfg(feature = "defmt")]
+        ::defmt::warn!($s $(, $x)*);
+        #[cfg(feature = "log")]
+        ::log::warn!($s $(, $x)*);
+        #[cfg(not(any(feature="defmt", feature="log")))]
+        let _ = ($( & $x ),*);
+    };
+}
+
+#[collapse_debuginfo(yes)]
+macro_rules! error {
+    ($s:literal $(, $x:expr)* $(,)?) => {
+        #[cfg(feature = "defmt")]
+        ::defmt::error!($s $(, $x)*);
+        #[cfg(feature = "log")]
+        ::log::error!($s $(, $x)*);
+        #[cfg(not(any(feature="defmt", feature="log")))]
+        let _ = ($( & $x ),*);
+    };
+}

Software/MainBoard/rust/src/mcutie_3_0_0/homeassistant/binary_sensor.rs

@@ -0,0 +1,120 @@
+//! Tools for publishing a [Home Assistant binary sensor](https://www.home-assistant.io/integrations/binary_sensor.mqtt/).
+use core::ops::Deref;
+
+use serde::{Deserialize, Serialize};
+
+use crate::{homeassistant::Component, Error, Publishable, Topic};
+
+/// The state of the sensor. Can be easily converted to or from a [`bool`].
+#[derive(Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(from = "&str", into = "&'static str")]
+#[allow(missing_docs)]
+pub enum BinarySensorState {
+    On,
+    Off,
+}
+
+impl From<BinarySensorState> for &'static str {
+    fn from(state: BinarySensorState) -> Self {
+        match state {
+            BinarySensorState::On => "ON",
+            BinarySensorState::Off => "OFF",
+        }
+    }
+}
+
+impl<'a> From<&'a str> for BinarySensorState {
+    fn from(st: &'a str) -> Self {
+        if st == "ON" {
+            Self::On
+        } else {
+            Self::Off
+        }
+    }
+}
+
+impl From<bool> for BinarySensorState {
+    fn from(val: bool) -> Self {
+        if val {
+            BinarySensorState::On
+        } else {
+            BinarySensorState::Off
+        }
+    }
+}
+
+impl From<BinarySensorState> for bool {
+    fn from(val: BinarySensorState) -> Self {
+        match val {
+            BinarySensorState::On => true,
+            BinarySensorState::Off => true,
+        }
+    }
+}
+
+impl AsRef<[u8]> for BinarySensorState {
+    fn as_ref(&self) -> &'static [u8] {
+        match self {
+            Self::On => "ON".as_bytes(),
+            Self::Off => "OFF".as_bytes(),
+        }
+    }
+}
+
+/// The type of sensor.
+#[derive(Serialize)]
+#[serde(rename_all = "snake_case")]
+#[allow(missing_docs)]
+pub enum BinarySensorClass {
+    Battery,
+    BatteryCharging,
+    CarbonMonoxide,
+    Cold,
+    Connectivity,
+    Door,
+    GarageDoor,
+    Gas,
+    Heat,
+    Light,
+    Lock,
+    Moisture,
+    Motion,
+    Moving,
+    Occupancy,
+    Opening,
+    Plug,
+    Power,
+    Presence,
+    Problem,
+    Running,
+    Safety,
+    Smoke,
+    Sound,
+    Tamper,
+    Update,
+    Vibration,
+    Window,
+}
+
+/// A binary sensor that can publish a [`BinarySensorState`] status.
+#[derive(Serialize)]
+pub struct BinarySensor {
+    /// The type of sensor
+    pub device_class: Option<BinarySensorClass>,
+}
+
+impl Component for BinarySensor {
+    type State = BinarySensorState;
+
+    fn platform() -> &'static str {
+        "binary_sensor"
+    }
+
+    async fn publish_state<T: Deref<Target = str>>(
+        &self,
+        topic: &Topic<T>,
+        state: Self::State,
+    ) -> Result<(), Error> {
+        topic.with_bytes(state).publish().await
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/homeassistant/button.rs

@@ -0,0 +1,40 @@
+//! Tools for publishing a [Home Assistant button](https://www.home-assistant.io/integrations/button.mqtt/).
+use core::ops::Deref;
+
+use serde::Serialize;
+
+use crate::{homeassistant::Component, Error, Topic};
+
+/// The type of button.
+#[derive(Serialize)]
+#[serde(rename_all = "snake_case")]
+#[allow(missing_docs)]
+pub enum ButtonClass {
+    Identify,
+    Restart,
+    Update,
+}
+
+/// A button that can be pressed.
+#[derive(Serialize)]
+pub struct Button {
+    /// The type of button.
+    pub device_class: Option<ButtonClass>,
+}
+
+impl Component for Button {
+    type State = ();
+
+    fn platform() -> &'static str {
+        "button"
+    }
+
+    async fn publish_state<T: Deref<Target = str>>(
+        &self,
+        _topic: &Topic<T>,
+        _state: Self::State,
+    ) -> Result<(), Error> {
+        // Buttons don't have a state
+        Err(Error::Invalid)
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/homeassistant/light.rs

@@ -0,0 +1,384 @@
+//! Tools for publishing a [Home Assistant light](https://www.home-assistant.io/integrations/light.mqtt/).
+use core::{ops::Deref, str};
+
+use serde::{ser::SerializeStruct, Deserialize, Serialize, Serializer};
+
+use crate::{
+    fmt::Debug2Format,
+    homeassistant::{binary_sensor::BinarySensorState, ser::List, Component},
+    Error, Payload, Publishable, Topic,
+};
+
+#[derive(Serialize)]
+#[serde(rename_all = "lowercase")]
+#[allow(missing_docs)]
+pub enum SupportedColorMode {
+    OnOff,
+    Brightness,
+    #[serde(rename = "color_temp")]
+    ColorTemp,
+    Hs,
+    Xy,
+    Rgb,
+    Rgbw,
+    Rgbww,
+    White,
+}
+
+#[derive(Serialize, Deserialize, Default)]
+struct SerializedColor {
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    h: Option<f32>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    s: Option<f32>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    x: Option<f32>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    y: Option<f32>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    r: Option<u8>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    g: Option<u8>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    b: Option<u8>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    w: Option<u8>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    c: Option<u8>,
+}
+
+#[derive(Deserialize)]
+struct LedPayload<'a> {
+    state: BinarySensorState,
+    #[serde(default)]
+    brightness: Option<u8>,
+    #[serde(default)]
+    color_temp: Option<u32>,
+    #[serde(default)]
+    color: Option<SerializedColor>,
+    #[serde(default)]
+    effect: Option<&'a str>,
+}
+
+/// The color of the light in various forms.
+#[derive(Serialize)]
+#[serde(rename_all = "lowercase", tag = "color_mode", content = "color")]
+#[allow(missing_docs)]
+pub enum Color {
+    None,
+    Brightness(u8),
+    ColorTemp(u32),
+    Hs {
+        #[serde(rename = "h")]
+        hue: f32,
+        #[serde(rename = "s")]
+        saturation: f32,
+    },
+    Xy {
+        x: f32,
+        y: f32,
+    },
+    Rgb {
+        #[serde(rename = "r")]
+        red: u8,
+        #[serde(rename = "g")]
+        green: u8,
+        #[serde(rename = "b")]
+        blue: u8,
+    },
+    Rgbw {
+        #[serde(rename = "r")]
+        red: u8,
+        #[serde(rename = "g")]
+        green: u8,
+        #[serde(rename = "b")]
+        blue: u8,
+        #[serde(rename = "w")]
+        white: u8,
+    },
+    Rgbww {
+        #[serde(rename = "r")]
+        red: u8,
+        #[serde(rename = "g")]
+        green: u8,
+        #[serde(rename = "b")]
+        blue: u8,
+        #[serde(rename = "c")]
+        cool_white: u8,
+        #[serde(rename = "w")]
+        warm_white: u8,
+    },
+}
+
+/// The state of the light. This can be sent to the broker and received as a
+/// command from Home Assistant.
+pub struct LightState<'a> {
+    /// Whether the light is on or off.
+    pub state: BinarySensorState,
+    /// The color of the light.
+    pub color: Color,
+    /// Any effect that is applied.
+    pub effect: Option<&'a str>,
+}
+
+impl<'a> LightState<'a> {
+    /// Parses the state from a command payload.
+    pub fn from_payload(payload: &'a Payload) -> Result<Self, Error> {
+        let parsed: LedPayload<'a> = match payload.deserialize_json() {
+            Ok(p) => p,
+            Err(e) => {
+                warn!("Failed to deserialize packet: {:?}", Debug2Format(&e));
+                if let Ok(s) = str::from_utf8(payload) {
+                    trace!("{}", s);
+                }
+                return Err(Error::PacketError);
+            }
+        };
+
+        let color = if let Some(color) = parsed.color {
+            if let Some(x) = color.x {
+                Color::Xy {
+                    x,
+                    y: color.y.unwrap_or_default(),
+                }
+            } else if let Some(h) = color.h {
+                Color::Hs {
+                    hue: h,
+                    saturation: color.s.unwrap_or_default(),
+                }
+            } else if let Some(c) = color.c {
+                Color::Rgbww {
+                    red: color.r.unwrap_or_default(),
+                    green: color.g.unwrap_or_default(),
+                    blue: color.b.unwrap_or_default(),
+                    cool_white: c,
+                    warm_white: color.w.unwrap_or_default(),
+                }
+            } else if let Some(w) = color.w {
+                Color::Rgbw {
+                    red: color.r.unwrap_or_default(),
+                    green: color.g.unwrap_or_default(),
+                    blue: color.b.unwrap_or_default(),
+                    white: w,
+                }
+            } else {
+                Color::Rgb {
+                    red: color.r.unwrap_or_default(),
+                    green: color.g.unwrap_or_default(),
+                    blue: color.b.unwrap_or_default(),
+                }
+            }
+        } else if let Some(color_temp) = parsed.color_temp {
+            Color::ColorTemp(color_temp)
+        } else if let Some(brightness) = parsed.brightness {
+            Color::Brightness(brightness)
+        } else {
+            Color::None
+        };
+
+        Ok(LightState {
+            state: parsed.state,
+            color,
+            effect: parsed.effect,
+        })
+    }
+}
+
+impl Serialize for LightState<'_> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let mut len = 1;
+
+        if self.effect.is_some() {
+            len += 1;
+        }
+
+        match self.color {
+            Color::None => {}
+            Color::Brightness(_) | Color::ColorTemp(_) => len += 1,
+            _ => len += 2,
+        }
+
+        let mut serializer = serializer.serialize_struct("LightState", len)?;
+
+        serializer.serialize_field("state", &self.state)?;
+
+        if let Some(effect) = self.effect {
+            serializer.serialize_field("effect", effect)?;
+        } else {
+            serializer.skip_field("effect")?;
+        }
+
+        match self.color {
+            Color::None => {
+                serializer.skip_field("brightness")?;
+                serializer.skip_field("color_temp")?;
+                serializer.skip_field("color")?;
+            }
+            Color::Brightness(b) => {
+                serializer.skip_field("color_temp")?;
+                serializer.skip_field("color")?;
+
+                serializer.serialize_field("brightness", &b)?
+            }
+            Color::ColorTemp(c) => {
+                serializer.skip_field("brightness")?;
+                serializer.skip_field("color")?;
+
+                serializer.serialize_field("color_temp", &c)?
+            }
+            Color::Hs { hue, saturation } => {
+                serializer.skip_field("brightness")?;
+                serializer.skip_field("color_temp")?;
+
+                serializer.serialize_field("color_mode", "hs")?;
+
+                let color = SerializedColor {
+                    h: Some(hue),
+                    s: Some(saturation),
+                    ..Default::default()
+                };
+
+                serializer.serialize_field("color", &color)?
+            }
+            Color::Xy { x, y } => {
+                serializer.skip_field("brightness")?;
+                serializer.skip_field("color_temp")?;
+
+                serializer.serialize_field("color_mode", "xy")?;
+
+                let color = SerializedColor {
+                    x: Some(x),
+                    y: Some(y),
+                    ..Default::default()
+                };
+
+                serializer.serialize_field("color", &color)?
+            }
+            Color::Rgb { red, green, blue } => {
+                serializer.skip_field("brightness")?;
+                serializer.skip_field("color_temp")?;
+
+                serializer.serialize_field("color_mode", "rgb")?;
+
+                let color = SerializedColor {
+                    r: Some(red),
+                    g: Some(green),
+                    b: Some(blue),
+                    ..Default::default()
+                };
+
+                serializer.serialize_field("color", &color)?
+            }
+            Color::Rgbw {
+                red,
+                green,
+                blue,
+                white,
+            } => {
+                serializer.skip_field("brightness")?;
+                serializer.skip_field("color_temp")?;
+
+                serializer.serialize_field("color_mode", "rgbw")?;
+
+                let color = SerializedColor {
+                    r: Some(red),
+                    g: Some(green),
+                    b: Some(blue),
+                    w: Some(white),
+                    ..Default::default()
+                };
+
+                serializer.serialize_field("color", &color)?
+            }
+            Color::Rgbww {
+                red,
+                green,
+                blue,
+                cool_white,
+                warm_white,
+            } => {
+                serializer.skip_field("brightness")?;
+                serializer.skip_field("color_temp")?;
+
+                serializer.serialize_field("color_mode", "rgbww")?;
+
+                let color = SerializedColor {
+                    r: Some(red),
+                    g: Some(green),
+                    b: Some(blue),
+                    c: Some(cool_white),
+                    w: Some(warm_white),
+                    ..Default::default()
+                };
+
+                serializer.serialize_field("color", &color)?
+            }
+        }
+
+        serializer.end()
+    }
+}
+
+/// A light entity
+pub struct Light<'a, const C: usize, const E: usize> {
+    /// The color modes supported by the light.
+    pub supported_color_modes: [SupportedColorMode; C],
+    /// Any effects that can be used.
+    pub effects: [&'a str; E],
+}
+
+impl<const C: usize, const E: usize> Serialize for Light<'_, C, E> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let mut len = 2;
+
+        if C > 0 {
+            len += 1;
+        }
+
+        if E > 0 {
+            len += 2;
+        }
+
+        let mut serializer = serializer.serialize_struct("Light", len)?;
+
+        serializer.serialize_field("schema", "json")?;
+
+        if C > 0 {
+            serializer.serialize_field("sup_clrm", &List::new(&self.supported_color_modes))?;
+        } else {
+            serializer.skip_field("sup_clrm")?;
+        }
+
+        if E > 0 {
+            serializer.serialize_field("effect", &true)?;
+            serializer.serialize_field("fx_list", &List::new(&self.effects))?;
+        } else {
+            serializer.skip_field("effect")?;
+            serializer.skip_field("fx_list")?;
+        }
+
+        serializer.end()
+    }
+}
+
+impl<const C: usize, const E: usize> Component for Light<'_, C, E> {
+    type State = LightState<'static>;
+
+    fn platform() -> &'static str {
+        "light"
+    }
+
+    async fn publish_state<T: Deref<Target = str>>(
+        &self,
+        topic: &Topic<T>,
+        state: Self::State,
+    ) -> Result<(), Error> {
+        topic.with_json(state).publish().await
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/homeassistant/mod.rs

@@ -0,0 +1,295 @@
+//! Home Assistant auto-discovery and related messages.
+//!
+//! Normally you would declare your entities statically in your binary. It is
+//! then trivial to send out discovery messages or state changes.
+//!
+//! ```
+//! # use mcutie::{Publishable, Topic};
+//! # use mcutie::homeassistant::{Entity, Device, Origin, AvailabilityState, AvailabilityTopics};
+//! # use mcutie::homeassistant::binary_sensor::{BinarySensor, BinarySensorClass, BinarySensorState};
+//! const DEVICE_AVAILABILITY_TOPIC: Topic<&'static str> = Topic::Device("status");
+//! const MOTION_STATE_TOPIC: Topic<&'static str> = Topic::Device("motion/status");
+//!
+//! const DEVICE: Device<'static> = Device::new();
+//! const ORIGIN: Origin<'static> = Origin::new();
+//!
+//! const MOTION_SENSOR: Entity<'static, 1, BinarySensor> = Entity {
+//!     device: DEVICE,
+//!     origin: ORIGIN,
+//!     object_id: "motion",
+//!     unique_id: Some("motion"),
+//!     name: "Motion",
+//!     availability: AvailabilityTopics::All([DEVICE_AVAILABILITY_TOPIC]),
+//!     state_topic: Some(MOTION_STATE_TOPIC),
+//!     command_topic: None,
+//!     component: BinarySensor {
+//!         device_class: Some(BinarySensorClass::Motion),
+//!     },
+//! };
+//!
+//! async fn send_discovery_messages() {
+//!     MOTION_SENSOR.publish_discovery().await.unwrap();
+//!     DEVICE_AVAILABILITY_TOPIC.with_bytes(AvailabilityState::Online).publish().await.unwrap();
+//! }
+//!
+//! async fn send_state(state: BinarySensorState) {
+//!     MOTION_SENSOR.publish_state(state).await.unwrap();
+//! }
+//! ```
+use core::{future::Future, ops::Deref};
+
+use mqttrs::QoS;
+use serde::{
+    ser::{Error as _, SerializeStruct},
+    Serialize, Serializer,
+};
+
+use crate::{
+    device_id, device_type, homeassistant::ser::DiscoverySerializer, io::publish, Error,
+    McutieTask, MqttMessage, Payload, Publishable, Topic, TopicString, DATA_CHANNEL,
+};
+
+pub mod binary_sensor;
+pub mod button;
+pub mod light;
+pub mod sensor;
+mod ser;
+
+const HA_STATUS_TOPIC: Topic<&'static str> = Topic::General("homeassistant/status");
+const STATE_ONLINE: &str = "online";
+const STATE_OFFLINE: &str = "offline";
+
+/// A trait representing a specific type of entity in Home Assistant
+pub trait Component: Serialize {
+    /// The state to publish.
+    type State;
+
+    /// The platform identifier for this entity. Internal.
+    fn platform() -> &'static str;
+
+    /// Publishes this entity's state to the MQTT broker.
+    fn publish_state<T: Deref<Target = str>>(
+        &self,
+        topic: &Topic<T>,
+        state: Self::State,
+    ) -> impl Future<Output = Result<(), Error>>;
+}
+
+impl<'t, T, L, const S: usize> McutieTask<'t, T, L, S>
+where
+    T: Deref<Target = str> + 't,
+    L: Publishable + 't,
+{
+    pub(super) async fn ha_after_connected(&self) {
+        let _ = HA_STATUS_TOPIC.subscribe(false).await;
+    }
+
+    pub(super) async fn ha_handle_update(
+        &self,
+        topic: &Topic<TopicString>,
+        payload: &Payload,
+    ) -> bool {
+        if topic == &HA_STATUS_TOPIC {
+            if payload.as_ref() == STATE_ONLINE.as_bytes() {
+                DATA_CHANNEL.send(MqttMessage::HomeAssistantOnline).await;
+            }
+
+            true
+        } else {
+            false
+        }
+    }
+}
+
+impl<T: Deref<Target = str>> Serialize for Topic<T> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer,
+    {
+        let mut topic = TopicString::new();
+        self.to_string(&mut topic)
+            .map_err(|_| S::Error::custom("topic was too large to serialize"))?;
+        serializer.serialize_str(&topic)
+    }
+}
+
+fn name_or_device<S>(name: &Option<&str>, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+{
+    serializer.serialize_str(name.unwrap_or_else(|| device_type()))
+}
+
+/// Represents the device in Home Assistant.
+///
+/// Can just be the default in which case useful properties such as the ID are
+/// automatically included.
+#[derive(Clone, Copy, Default)]
+pub struct Device<'a> {
+    /// A name to identify the device. If not provided the default device type is
+    /// used.
+    pub name: Option<&'a str>,
+    /// An optional configuration URL for the device.
+    pub configuration_url: Option<&'a str>,
+}
+
+impl Device<'_> {
+    /// Creates a new default device.
+    pub const fn new() -> Self {
+        Self {
+            name: None,
+            configuration_url: None,
+        }
+    }
+}
+
+impl Serialize for Device<'_> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let mut len = 2;
+        if self.configuration_url.is_some() {
+            len += 1;
+        }
+
+        let mut serializer = serializer.serialize_struct("Device", len)?;
+
+        serializer.serialize_field("name", self.name.unwrap_or_else(|| device_type()))?;
+        serializer.serialize_field("ids", device_id())?;
+
+        if let Some(cu) = self.configuration_url {
+            serializer.serialize_field("cu", cu)?;
+        } else {
+            serializer.skip_field("cu")?;
+        }
+
+        serializer.end()
+    }
+}
+
+/// Represents the device's origin in Home Assistant.
+///
+/// Can just be the default in which case useful properties are automatically
+/// included.
+#[derive(Clone, Copy, Default, Serialize)]
+pub struct Origin<'a> {
+    /// A name to identify the device's origin. If not provided the default
+    /// device type is used.
+    #[serde(serialize_with = "name_or_device")]
+    pub name: Option<&'a str>,
+}
+
+impl Origin<'_> {
+    /// Creates a new default origin.
+    pub const fn new() -> Self {
+        Self { name: None }
+    }
+}
+
+/// A single entity for Home Assistant.
+///
+/// Calling [`Entity::publish_discovery`] will publish the discovery message to
+/// allow Home Assistant to detect this entity. Read the
+/// [Home Assistant MQTT docs](https://www.home-assistant.io/integrations/mqtt/)
+/// for information on what some of these properties mean.
+pub struct Entity<'a, const A: usize, C: Component> {
+    /// The device this entity is a part of.
+    pub device: Device<'a>,
+    /// The origin of the device.
+    pub origin: Origin<'a>,
+    /// An object identifier to allow for entity ID customisation in Home Assistant.
+    pub object_id: &'a str,
+    /// An optional unique identifier for the entity.
+    pub unique_id: Option<&'a str>,
+    /// A friendly name for the entity.
+    pub name: &'a str,
+    /// Specifies the availability topics that Home Assistant will listen to to
+    /// determine this entity's availability.
+    pub availability: AvailabilityTopics<'a, A>,
+    /// The state topic that this entity's state is published to.
+    pub state_topic: Option<Topic<&'a str>>,
+    /// The command topic that this entity receives commands from.
+    pub command_topic: Option<Topic<&'a str>>,
+    /// The specific entity.
+    pub component: C,
+}
+
+impl<const A: usize, C: Component> Entity<'_, A, C> {
+    /// Publishes the discovery message for this entity to the broker.
+    pub async fn publish_discovery(&self) -> Result<(), Error> {
+        let mut topic = TopicString::new();
+        topic
+            .push_str(option_env!("HA_DISCOVERY_PREFIX").unwrap_or("homeassistant"))
+            .map_err(|_| Error::TooLarge)?;
+        topic.push('/').map_err(|_| Error::TooLarge)?;
+        topic.push_str(C::platform()).map_err(|_| Error::TooLarge)?;
+        topic.push('/').map_err(|_| Error::TooLarge)?;
+        topic
+            .push_str(self.object_id)
+            .map_err(|_| Error::TooLarge)?;
+        topic.push_str("/config").map_err(|_| Error::TooLarge)?;
+
+        let mut payload = Payload::new();
+        payload.serialize_json(self).map_err(|_| Error::TooLarge)?;
+
+        publish(&topic, &payload, QoS::AtMostOnce, false).await
+    }
+
+    /// Publishes this entity's state to the broker.
+    ///
+    /// # Errors
+    ///
+    /// - [`Error::Invalid`] if the entity doesn't have a state topic.
+    pub async fn publish_state(&self, state: C::State) -> Result<(), Error> {
+        if let Some(topic) = self.state_topic {
+            self.component.publish_state(&topic, state).await
+        } else {
+            Err(Error::Invalid)
+        }
+    }
+}
+
+/// A payload representing a device or entity's availability.
+#[allow(missing_docs)]
+pub enum AvailabilityState {
+    Online,
+    Offline,
+}
+
+impl AsRef<[u8]> for AvailabilityState {
+    fn as_ref(&self) -> &'static [u8] {
+        match self {
+            Self::Online => STATE_ONLINE.as_bytes(),
+            Self::Offline => STATE_OFFLINE.as_bytes(),
+        }
+    }
+}
+
+/// The availiabity topics that home assistant will use to determine an entity's
+/// availability.
+pub enum AvailabilityTopics<'a, const A: usize> {
+    /// The entity is always available.
+    None,
+    /// The entity is available if all of the topics are publishes as online.
+    All([Topic<&'a str>; A]),
+    /// The entity is available if any of the topics are publishes as online.
+    Any([Topic<&'a str>; A]),
+    /// The entity is available based on the most recent of the topics to
+    /// publish state.
+    Latest([Topic<&'a str>; A]),
+}
+
+impl<const A: usize, C: Component> Serialize for Entity<'_, A, C> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let outer = DiscoverySerializer {
+            discovery: self,
+            inner: serializer,
+        };
+
+        self.component.serialize(outer)
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/homeassistant/sensor.rs

@@ -0,0 +1,103 @@
+//! Tools for publishing a [Home Assistant sensor](https://www.home-assistant.io/integrations/sensor.mqtt/).
+use core::ops::Deref;
+
+use serde::Serialize;
+
+use crate::{homeassistant::Component, Error, Publishable, Topic};
+
+/// The type of sensor.
+#[derive(Serialize)]
+#[serde(rename_all = "snake_case")]
+#[allow(missing_docs)]
+pub enum SensorClass {
+    ApparentPower,
+    Aqi,
+    AtmosphericPressure,
+    Battery,
+    CarbonDioxide,
+    CarbonMonoxide,
+    Current,
+    DataRate,
+    DataSize,
+    Date,
+    Distance,
+    Duration,
+    Energy,
+    EnergyStorage,
+    Enum,
+    Frequency,
+    Gas,
+    Humidity,
+    Illuminance,
+    Irradiance,
+    Moisture,
+    Monetary,
+    NitrogenDioxide,
+    NitrogenMonoxide,
+    NitrousOxide,
+    Ozone,
+    Ph,
+    Pm1,
+    Pm25,
+    Pm10,
+    PowerFactor,
+    Power,
+    Precipitation,
+    PrecipitationIntensity,
+    Pressure,
+    ReactivePower,
+    SignalStrength,
+    SoundPressure,
+    Speed,
+    SulphurDioxide,
+    Temperature,
+    Timestamp,
+    VolatileOrganicCompounds,
+    VolatileOrganicCompoundsParts,
+    Voltage,
+    Volume,
+    VolumeFlowRate,
+    VolumeStorage,
+    Water,
+    Weight,
+    WindSpeed,
+}
+
+/// The type of measurement that this entity publishes.
+#[derive(Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum SensorStateClass {
+    /// A measurement at a singe point in time.
+    Measurement,
+    /// A cumulative total that can increase or decrease over time.
+    Total,
+    /// A cumulative total that can only increase.
+    TotalIncreasing,
+}
+
+/// A binary sensor that can publish a [`f32`] value.
+#[derive(Serialize)]
+pub struct Sensor<'u> {
+    /// The type of sensor.
+    pub device_class: Option<SensorClass>,
+    /// The type of measurement that this sensor reports.
+    pub state_class: Option<SensorStateClass>,
+    /// The unit of measurement for this sensor.
+    pub unit_of_measurement: Option<&'u str>,
+}
+
+impl Component for Sensor<'_> {
+    type State = f32;
+
+    fn platform() -> &'static str {
+        "sensor"
+    }
+
+    async fn publish_state<T: Deref<Target = str>>(
+        &self,
+        topic: &Topic<T>,
+        state: Self::State,
+    ) -> Result<(), Error> {
+        topic.with_display(state).publish().await
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/homeassistant/ser.rs

@@ -0,0 +1,333 @@
+use core::ops::Deref;
+
+use serde::{
+    ser::{SerializeSeq, SerializeStruct},
+    Serialize, Serializer,
+};
+
+use crate::{
+    homeassistant::{AvailabilityTopics, Component, Entity},
+    Topic,
+};
+
+#[derive(Serialize)]
+pub(super) struct AvailabilityTopicItem<'a> {
+    topic: Topic<&'a str>,
+}
+
+struct AvailabilityTopicList<'a, T: Deref<Target = str>, const N: usize> {
+    list: &'a [Topic<T>; N],
+}
+
+impl<'a, const N: usize, T: Deref<Target = str>> AvailabilityTopicList<'a, T, N> {
+    pub(super) fn new(list: &'a [Topic<T>; N]) -> Self {
+        Self { list }
+    }
+}
+
+impl<T: Deref<Target = str>, const N: usize> Serialize for AvailabilityTopicList<'_, T, N> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let mut serializer = serializer.serialize_seq(Some(N))?;
+
+        for topic in self.list {
+            serializer.serialize_element(&AvailabilityTopicItem {
+                topic: topic.as_ref(),
+            })?;
+        }
+
+        serializer.end()
+    }
+}
+
+pub(super) struct List<'a, T: Serialize, const N: usize> {
+    list: &'a [T; N],
+}
+
+impl<'a, T: Serialize, const N: usize> List<'a, T, N> {
+    pub(super) fn new(list: &'a [T; N]) -> Self {
+        Self { list }
+    }
+}
+
+impl<T: Serialize, const N: usize> Serialize for List<'_, T, N> {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let mut serializer = serializer.serialize_seq(Some(N))?;
+
+        for item in self.list {
+            serializer.serialize_element(item)?;
+        }
+
+        serializer.end()
+    }
+}
+
+pub(super) struct DiscoverySerializer<'a, const A: usize, C: Component, S: Serializer> {
+    pub(super) discovery: &'a Entity<'a, A, C>,
+    pub(super) inner: S,
+}
+
+impl<const A: usize, C: Component, S: Serializer> Serializer for DiscoverySerializer<'_, A, C, S> {
+    type Ok = S::Ok;
+    type Error = S::Error;
+    type SerializeSeq = S::SerializeSeq;
+    type SerializeTuple = S::SerializeTuple;
+    type SerializeTupleStruct = S::SerializeTupleStruct;
+    type SerializeTupleVariant = S::SerializeTupleVariant;
+    type SerializeMap = S::SerializeMap;
+    type SerializeStruct = S::SerializeStruct;
+    type SerializeStructVariant = S::SerializeStructVariant;
+
+    fn serialize_struct(
+        self,
+        name: &'static str,
+        mut len: usize,
+    ) -> Result<Self::SerializeStruct, Self::Error> {
+        len += 5;
+        if self.discovery.state_topic.is_some() {
+            len += 1;
+        }
+        if self.discovery.command_topic.is_some() {
+            len += 1;
+        }
+        if self.discovery.unique_id.is_some() {
+            len += 1;
+        }
+        if !matches!(self.discovery.availability, AvailabilityTopics::None) {
+            len += 2;
+        }
+
+        let mut serializer = self.inner.serialize_struct(name, len)?;
+
+        serializer.serialize_field("dev", &self.discovery.device)?;
+        serializer.serialize_field("o", &self.discovery.origin)?;
+        serializer.serialize_field("p", C::platform())?;
+        serializer.serialize_field("obj_id", self.discovery.object_id)?;
+
+        serializer.serialize_field("name", self.discovery.name)?;
+
+        if let Some(t) = self.discovery.state_topic {
+            serializer.serialize_field("stat_t", &t)?;
+        } else {
+            serializer.skip_field("stat_t")?;
+        }
+
+        if let Some(t) = self.discovery.command_topic {
+            serializer.serialize_field("cmd_t", &t)?;
+        } else {
+            serializer.skip_field("cmd_t")?;
+        }
+
+        match &self.discovery.availability {
+            AvailabilityTopics::None => {
+                serializer.skip_field("avty")?;
+                serializer.skip_field("avty_mode")?;
+            }
+            AvailabilityTopics::All(topics) => {
+                serializer.serialize_field("avty_mode", "all")?;
+                serializer.serialize_field("avty", &AvailabilityTopicList::new(topics))?;
+            }
+            AvailabilityTopics::Any(topics) => {
+                serializer.serialize_field("avty_mode", "any")?;
+                serializer.serialize_field("avty", &AvailabilityTopicList::new(topics))?;
+            }
+            AvailabilityTopics::Latest(topics) => {
+                serializer.serialize_field("avty_mode", "latest")?;
+                serializer.serialize_field("avty", &AvailabilityTopicList::new(topics))?;
+            }
+        }
+
+        if let Some(v) = self.discovery.unique_id {
+            serializer.serialize_field("uniq_id", v)?;
+        } else {
+            serializer.skip_field("uniq_id")?;
+        }
+
+        Ok(serializer)
+    }
+
+    fn serialize_bool(self, _: bool) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_i8(self, _: i8) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_i16(self, _: i16) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_i32(self, _: i32) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_i64(self, _: i64) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_u8(self, _: u8) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_u16(self, _: u16) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_u32(self, _: u32) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_u64(self, _: u64) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_f32(self, _: f32) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_f64(self, _: f64) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_char(self, _: char) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_str(self, _: &str) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_bytes(self, _: &[u8]) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_none(self) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_some<T>(self, _: &T) -> Result<Self::Ok, Self::Error>
+    where
+        T: ?Sized + Serialize,
+    {
+        unimplemented!()
+    }
+
+    fn serialize_unit(self) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_unit_struct(self, _: &'static str) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _: &'static str,
+        _: u32,
+        _: &'static str,
+    ) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_newtype_struct<T>(self, _: &'static str, _: &T) -> Result<Self::Ok, Self::Error>
+    where
+        T: ?Sized + Serialize,
+    {
+        unimplemented!()
+    }
+
+    fn serialize_newtype_variant<T>(
+        self,
+        _: &'static str,
+        _: u32,
+        _: &'static str,
+        _: &T,
+    ) -> Result<Self::Ok, Self::Error>
+    where
+        T: ?Sized + Serialize,
+    {
+        unimplemented!()
+    }
+
+    fn serialize_seq(self, _: Option<usize>) -> Result<Self::SerializeSeq, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_tuple(self, _: usize) -> Result<Self::SerializeTuple, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _: &'static str,
+        _: usize,
+    ) -> Result<Self::SerializeTupleStruct, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _: &'static str,
+        _: u32,
+        _: &'static str,
+        _: usize,
+    ) -> Result<Self::SerializeTupleVariant, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_map(self, _: Option<usize>) -> Result<Self::SerializeMap, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _: &'static str,
+        _: u32,
+        _: &'static str,
+        _: usize,
+    ) -> Result<Self::SerializeStructVariant, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_i128(self, _: i128) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn serialize_u128(self, _: u128) -> Result<Self::Ok, Self::Error> {
+        unimplemented!()
+    }
+
+    fn collect_seq<I>(self, _: I) -> Result<Self::Ok, Self::Error>
+    where
+        I: IntoIterator,
+        <I as IntoIterator>::Item: Serialize,
+    {
+        unimplemented!()
+    }
+
+    fn collect_map<K, V, I>(self, _: I) -> Result<Self::Ok, Self::Error>
+    where
+        K: Serialize,
+        V: Serialize,
+        I: IntoIterator<Item = (K, V)>,
+    {
+        unimplemented!()
+    }
+
+    fn collect_str<T>(self, _: &T) -> Result<Self::Ok, Self::Error>
+    where
+        T: ?Sized + core::fmt::Display,
+    {
+        unimplemented!()
+    }
+
+    fn is_human_readable(&self) -> bool {
+        unimplemented!()
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/io.rs

@@ -0,0 +1,483 @@
+use core::ops::Deref;
+
+pub(crate) use atomic16::assign_pid;
+use embassy_futures::select::{select, select4, Either};
+use embassy_net::{
+    dns::DnsQueryType,
+    tcp::{TcpReader, TcpSocket, TcpWriter},
+    Stack,
+};
+use embassy_sync::{
+    blocking_mutex::raw::CriticalSectionRawMutex,
+    pubsub::{PubSubChannel, Subscriber, WaitResult},
+};
+use embassy_time::Timer;
+use embedded_io_async::Write;
+use mqttrs::{
+    decode_slice, Connect, ConnectReturnCode, LastWill, Packet, Pid, Protocol, Publish, QoS, QosPid,
+};
+
+use crate::{
+    device_id, fmt::Debug2Format, pipe::ConnectedPipe, ControlMessage, Error, MqttMessage, Payload,
+    Publishable, Topic, TopicString, CONFIRMATION_TIMEOUT, DATA_CHANNEL, DEFAULT_BACKOFF,
+    RESET_BACKOFF,
+};
+
+static SEND_QUEUE: ConnectedPipe<CriticalSectionRawMutex, Payload, 10> = ConnectedPipe::new();
+
+pub(crate) static CONTROL_CHANNEL: PubSubChannel<CriticalSectionRawMutex, ControlMessage, 2, 5, 0> =
+    PubSubChannel::new();
+
+type ControlSubscriber = Subscriber<'static, CriticalSectionRawMutex, ControlMessage, 2, 5, 0>;
+
+pub(crate) async fn subscribe() -> ControlSubscriber {
+    loop {
+        if let Ok(sub) = CONTROL_CHANNEL.subscriber() {
+            return sub;
+        }
+
+        Timer::after_millis(50).await;
+    }
+}
+
+#[cfg(target_has_atomic = "16")]
+mod atomic16 {
+    use core::sync::atomic::{AtomicU16, Ordering};
+
+    use mqttrs::Pid;
+
+    static PID: AtomicU16 = AtomicU16::new(0);
+
+    pub(crate) async fn assign_pid() -> Pid {
+        Pid::new() + PID.fetch_add(1, Ordering::SeqCst)
+    }
+}
+
+#[cfg(not(target_has_atomic = "16"))]
+mod atomic16 {
+    use embassy_sync::{blocking_mutex::raw::CriticalSectionRawMutex, mutex::Mutex};
+    use mqttrs::Pid;
+
+    static PID_MUTEX: Mutex<CriticalSectionRawMutex, u16> = Mutex::new(0);
+
+    pub(crate) async fn assign_pid() -> Pid {
+        let mut locked = PID_MUTEX.lock().await;
+        *locked += 1;
+
+        Pid::new() + *locked
+    }
+}
+
+pub(crate) async fn send_packet(packet: Packet<'_>) -> Result<(), Error> {
+    let mut buffer = Payload::new();
+
+    match buffer.encode_packet(&packet) {
+        Ok(()) => {
+            debug!(
+                "Sending packet to broker: {:?}",
+                Debug2Format(&packet.get_type())
+            );
+            SEND_QUEUE.push(buffer).await;
+            Ok(())
+        }
+        Err(_) => {
+            error!("Failed to send packet");
+            Err(Error::PacketError)
+        }
+    }
+}
+
+pub(crate) async fn wait_for_publish(
+    mut subscriber: ControlSubscriber,
+    expected_pid: Pid,
+) -> Result<(), Error> {
+    match select(
+        async {
+            loop {
+                match subscriber.next_message().await {
+                    WaitResult::Lagged(_) => {
+                        // Maybe we missed the message?
+                    }
+                    WaitResult::Message(ControlMessage::Published(published_pid)) => {
+                        if published_pid == expected_pid {
+                            return Ok(());
+                        }
+                    }
+                    _ => {}
+                }
+            }
+        },
+        Timer::after_millis(CONFIRMATION_TIMEOUT),
+    )
+    .await
+    {
+        Either::First(r) => r,
+        Either::Second(_) => Err(Error::TimedOut),
+    }
+}
+
+pub(crate) async fn publish(
+    topic_name: &str,
+    payload: &[u8],
+    qos: QoS,
+    retain: bool,
+) -> Result<(), Error> {
+    let subscriber = subscribe().await;
+
+    let (qospid, pid) = match qos {
+        QoS::AtMostOnce => (QosPid::AtMostOnce, None),
+        QoS::AtLeastOnce => {
+            let pid = assign_pid().await;
+            (QosPid::AtLeastOnce(pid), Some(pid))
+        }
+        QoS::ExactlyOnce => {
+            let pid = assign_pid().await;
+            (QosPid::ExactlyOnce(pid), Some(pid))
+        }
+    };
+
+    let packet = Packet::Publish(Publish {
+        dup: false,
+        qospid,
+        retain,
+        topic_name,
+        payload,
+    });
+
+    send_packet(packet).await?;
+
+    if let Some(expected_pid) = pid {
+        wait_for_publish(subscriber, expected_pid).await
+    } else {
+        Ok(())
+    }
+}
+
+fn packet_size(buffer: &[u8]) -> Option<usize> {
+    let mut pos = 1;
+    let mut multiplier = 1;
+    let mut value = 0;
+
+    while pos < buffer.len() {
+        value += (buffer[pos] & 127) as usize * multiplier;
+        multiplier *= 128;
+
+        if (buffer[pos] & 128) == 0 {
+            return Some(value + pos + 1);
+        }
+
+        pos += 1;
+        if pos == 5 {
+            return Some(0);
+        }
+    }
+
+    None
+}
+
+/// The MQTT task that must be run in order for the stack to operate.
+pub struct McutieTask<'t, T, L, const S: usize>
+where
+    T: Deref<Target = str> + 't,
+    L: Publishable + 't,
+{
+    pub(crate) network: Stack<'t>,
+    pub(crate) broker: &'t str,
+    pub(crate) last_will: Option<L>,
+    pub(crate) username: Option<&'t str>,
+    pub(crate) password: Option<&'t str>,
+    pub(crate) subscriptions: [Topic<T>; S],
+    pub(crate) keep_alive: u16
+}
+
+impl<'t, T, L, const S: usize> McutieTask<'t, T, L, S>
+where
+    T: Deref<Target = str> + 't,
+    L: Publishable + 't,
+{
+    #[cfg(not(feature = "homeassistant"))]
+    async fn ha_handle_update(&self, _topic: &Topic<TopicString>, _payload: &Payload) -> bool {
+        false
+    }
+
+    async fn recv_loop(&self, mut reader: TcpReader<'_>) -> Result<(), Error> {
+        let mut buffer = [0_u8; 4096];
+        let mut cursor: usize = 0;
+
+        let controller = CONTROL_CHANNEL.immediate_publisher();
+
+        loop {
+            match reader.read(&mut buffer[cursor..]).await {
+                Ok(0) => {
+                    error!("Receive socket closed");
+                    return Ok(());
+                }
+                Ok(len) => {
+                    cursor += len;
+                }
+                Err(_) => {
+                    error!("I/O failure reading packet");
+                    return Err(Error::IOError);
+                }
+            }
+
+            let mut start_pos = 0;
+            loop {
+                let packet_length = match packet_size(&buffer[start_pos..cursor]) {
+                    Some(0) => {
+                        error!("Invalid MQTT packet");
+                        return Err(Error::PacketError);
+                    }
+                    Some(len) => len,
+                    None => {
+                        // None is returned when there is not yet enough data to decode a packet.
+                        if start_pos != 0 {
+                            // Adjust the buffer to reclaim any unused data
+                            buffer.copy_within(start_pos..cursor, 0);
+                            cursor -= start_pos;
+                        }
+                        break;
+                    }
+                };
+
+                let packet = match decode_slice(&buffer[start_pos..(start_pos + packet_length)]) {
+                    Ok(Some(p)) => p,
+                    Ok(None) => {
+                        error!("Packet length calculation failed.");
+                        return Err(Error::PacketError);
+                    }
+                    Err(_) => {
+                        error!("Invalid MQTT packet");
+                        return Err(Error::PacketError);
+                    }
+                };
+
+                debug!(
+                    "Received packet from broker: {:?}",
+                    Debug2Format(&packet.get_type())
+                );
+
+                match packet {
+                    Packet::Connack(connack) => match connack.code {
+                        ConnectReturnCode::Accepted => {
+                            #[cfg(feature = "homeassistant")]
+                            self.ha_after_connected().await;
+
+                            for topic in &self.subscriptions {
+                                let _ = topic.subscribe(false).await;
+                            }
+
+                            DATA_CHANNEL.send(MqttMessage::Connected).await;
+                        }
+                        _ => {
+                            error!("Connection request to broker was not accepted");
+                            return Err(Error::IOError);
+                        }
+                    },
+                    Packet::Pingresp => {}
+
+                    Packet::Publish(publish) => {
+                        match (
+                            Topic::from_str(publish.topic_name),
+                            Payload::from(publish.payload),
+                        ) {
+                            (Ok(topic), Ok(payload)) => {
+                                if !self.ha_handle_update(&topic, &payload).await {
+                                    DATA_CHANNEL
+                                        .send(MqttMessage::Publish(topic, payload))
+                                        .await;
+                                }
+                            }
+                            _ => {
+                                error!("Unable to process publish data as it was too large");
+                            }
+                        }
+
+                        match publish.qospid {
+                            mqttrs::QosPid::AtMostOnce => {}
+                            mqttrs::QosPid::AtLeastOnce(pid) => {
+                                send_packet(Packet::Puback(pid)).await?;
+                            }
+                            mqttrs::QosPid::ExactlyOnce(pid) => {
+                                send_packet(Packet::Pubrec(pid)).await?;
+                            }
+                        }
+                    }
+                    Packet::Puback(pid) => {
+                        controller.publish_immediate(ControlMessage::Published(pid));
+                    }
+                    Packet::Pubrec(pid) => {
+                        controller.publish_immediate(ControlMessage::Published(pid));
+                        send_packet(Packet::Pubrel(pid)).await?;
+                    }
+                    Packet::Pubrel(pid) => send_packet(Packet::Pubrel(pid)).await?,
+                    Packet::Pubcomp(_) => {}
+
+                    Packet::Suback(suback) => {
+                        if let Some(return_code) = suback.return_codes.first() {
+                            controller.publish_immediate(ControlMessage::Subscribed(
+                                suback.pid,
+                                *return_code,
+                            ));
+                        } else {
+                            warn!("Unexpected suback with no return codes");
+                        }
+                    }
+                    Packet::Unsuback(pid) => {
+                        controller.publish_immediate(ControlMessage::Unsubscribed(pid));
+                    }
+
+                    Packet::Connect(_)
+                    | Packet::Subscribe(_)
+                    | Packet::Pingreq
+                    | Packet::Unsubscribe(_)
+                    | Packet::Disconnect => {
+                        debug!(
+                            "Unexpected packet from broker: {:?}",
+                            Debug2Format(&packet.get_type())
+                        );
+                    }
+                }
+
+                start_pos += packet_length;
+                if start_pos == cursor {
+                    cursor = 0;
+                    break;
+                }
+            }
+        }
+    }
+
+    async fn write_loop(&self, mut writer: TcpWriter<'_>) {
+        let mut buffer = Payload::new();
+
+        let mut last_will_topic = TopicString::new();
+        let mut last_will_payload = Payload::new();
+
+        let last_will = self.last_will.as_ref().and_then(|p| {
+            if p.write_topic(&mut last_will_topic).is_ok()
+                && p.write_payload(&mut last_will_payload).is_ok()
+            {
+                Some(LastWill {
+                    topic: &last_will_topic,
+                    message: &last_will_payload,
+                    qos: p.qos(),
+                    retain: p.retain(),
+                })
+            } else {
+                None
+            }
+        });
+
+        // Send our connection request.
+        if buffer
+            .encode_packet(&Packet::Connect(Connect {
+                protocol: Protocol::MQTT311,
+                keep_alive: self.keep_alive,
+                client_id: device_id(),
+                clean_session: true,
+                last_will,
+                username: self.username,
+                password: self.password.map(|s| s.as_bytes()),
+            }))
+            .is_err()
+        {
+            error!("Failed to encode connection packet");
+            return;
+        }
+
+        if let Err(e) = writer.write_all(&buffer).await {
+            error!("Failed to send connection packet: {:?}", e);
+            return;
+        }
+
+        let reader = SEND_QUEUE.reader();
+
+        loop {
+            let buffer = reader.receive().await;
+
+            trace!("Writer sending packet");
+            if let Err(e) = writer.write_all(&buffer).await {
+                error!("Failed to send data: {:?}", e);
+                return;
+            }
+        }
+    }
+
+    /// Runs the MQTT stack. The future returned from this must be awaited for everything to work.
+    pub async fn run(self) {
+        let mut timeout: Option<u64> = None;
+
+        let mut rx_buffer = [0; 4096];
+        let mut tx_buffer = [0; 4096];
+
+        loop {
+            if let Some(millis) = timeout.replace(DEFAULT_BACKOFF) {
+                Timer::after_millis(millis).await;
+            }
+
+            if !self.network.is_config_up() {
+                debug!("Waiting for network to configure.");
+                self.network.wait_config_up().await;
+                debug!("Network configured.");
+            }
+
+            let ip_addrs = match self.network.dns_query(self.broker, DnsQueryType::A).await {
+                Ok(v) => v,
+                Err(e) => {
+                    error!("Failed to lookup '{}' for broker: {:?}", self.broker, e);
+                    continue;
+                }
+            };
+
+            let ip = match ip_addrs.first() {
+                Some(i) => *i,
+                None => {
+                    error!("No IP address found for broker '{}'", self.broker);
+                    continue;
+                }
+            };
+
+            debug!("Connecting to {}:1883", ip);
+
+            let mut socket = TcpSocket::new(self.network, &mut rx_buffer, &mut tx_buffer);
+            if let Err(e) = socket.connect((ip, 1883)).await {
+                error!("Failed to connect to {}:1883: {:?}", ip, e);
+                continue;
+            }
+
+            info!("Connected to {}", self.broker);
+            timeout = Some(RESET_BACKOFF);
+
+            let (reader, writer) = socket.split();
+
+            let recv_loop = self.recv_loop(reader);
+            let send_loop = self.write_loop(writer);
+
+            let ping_loop = async {
+                loop {
+                    Timer::after_secs(45).await;
+
+                    let _ = send_packet(Packet::Pingreq).await;
+                }
+            };
+
+            let link_down = async {
+                self.network.wait_link_down().await;
+                warn!("Network link lost");
+            };
+
+            let ip_down = async {
+                self.network.wait_config_down().await;
+                warn!("Network config lost");
+            };
+
+            select4(send_loop, ping_loop, recv_loop, select(link_down, ip_down)).await;
+
+            socket.close();
+
+            warn!("Lost connection with broker");
+            DATA_CHANNEL.send(MqttMessage::Disconnected).await;
+        }
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/lib.rs

@@ -0,0 +1,227 @@
+#![no_std]
+#![deny(unreachable_pub)]
+#![warn(missing_docs)]
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+//! MQTT client support crate vendored into this repository.
+
+use core::{ops::Deref, str};
+
+pub use buffer::Buffer;
+use embassy_net::{HardwareAddress, Stack};
+use embassy_sync::{blocking_mutex::raw::CriticalSectionRawMutex, channel::Channel};
+use heapless::String;
+pub use io::McutieTask;
+pub use mqttrs::QoS;
+use mqttrs::{Pid, SubscribeReturnCodes};
+use once_cell::sync::OnceCell;
+pub use publish::*;
+pub use topic::Topic;
+
+// This must come first so the macros are visible
+pub(crate) mod fmt;
+
+mod buffer;
+#[cfg(feature = "homeassistant")]
+pub mod homeassistant;
+mod io;
+mod pipe;
+mod publish;
+mod topic;
+
+// This really needs to match that used by mqttrs.
+const TOPIC_LENGTH: usize = 256;
+const PAYLOAD_LENGTH: usize = 2048;
+
+/// A fixed length stack allocated string. The length is fixed by the mqttrs crate.
+pub type TopicString = String<TOPIC_LENGTH>;
+/// A fixed length buffer of 2048 bytes.
+pub type Payload = Buffer<PAYLOAD_LENGTH>;
+
+// By default in the event of an error connecting to the broker we will wait for 5s.
+const DEFAULT_BACKOFF: u64 = 5000;
+// If the connection dropped then re-connect more quickly.
+const RESET_BACKOFF: u64 = 200;
+// How long to wait for the broker to confirm actions.
+const CONFIRMATION_TIMEOUT: u64 = 2000;
+
+static DATA_CHANNEL: Channel<CriticalSectionRawMutex, MqttMessage, 10> = Channel::new();
+
+static DEVICE_TYPE: OnceCell<String<32>> = OnceCell::new();
+static DEVICE_ID: OnceCell<String<32>> = OnceCell::new();
+
+fn device_id() -> &'static str {
+    DEVICE_ID.get().unwrap()
+}
+
+fn device_type() -> &'static str {
+    DEVICE_TYPE.get().unwrap()
+}
+
+/// Various errors
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum Error {
+    /// An IO error occured.
+    IOError,
+    /// The operation timed out.
+    TimedOut,
+    /// An attempt was made to encode something too large.
+    TooLarge,
+    /// A packet or payload could not be decoded or encoded.
+    PacketError,
+    /// An invalid or unsupported operation was attempted.
+    Invalid,
+    /// A value was rejected.
+    Rejected,
+}
+
+#[allow(clippy::large_enum_variant)]
+/// A message from the MQTT broker.
+pub enum MqttMessage {
+    /// The broker has been connected to successfully. Generally in response to this message a
+    /// device should subscribe to topics of interest and send out any device state.
+    Connected,
+    /// New data received from the broker.
+    Publish(Topic<TopicString>, Payload),
+    /// The connection to the broker has been dropped.
+    Disconnected,
+    /// Home Assistant has come online and you should send any discovery messages.
+    #[cfg(feature = "homeassistant")]
+    HomeAssistantOnline,
+}
+
+#[derive(Clone)]
+enum ControlMessage {
+    Published(Pid),
+    Subscribed(Pid, SubscribeReturnCodes),
+    Unsubscribed(Pid),
+}
+
+/// Receives messages from the broker.
+pub struct McutieReceiver;
+
+impl McutieReceiver {
+    /// Waits for the next message from the broker.
+    pub async fn receive(&self) -> MqttMessage {
+        DATA_CHANNEL.receive().await
+    }
+}
+
+/// A builder to configure the MQTT stack.
+pub struct McutieBuilder<'t, T, L, const S: usize>
+where
+    T: Deref<Target = str> + 't,
+    L: Publishable + 't,
+{
+    network: Stack<'t>,
+    device_type: &'t str,
+    device_id: Option<&'t str>,
+    broker: &'t str,
+    last_will: Option<L>,
+    username: Option<&'t str>,
+    password: Option<&'t str>,
+    subscriptions: [Topic<T>; S],
+}
+
+impl<'t, T: Deref<Target = str> + 't, L: Publishable + 't> McutieBuilder<'t, T, L, 0> {
+    /// Creates a new builder with the initial required configuration.
+    ///
+    /// `device_type` is expected to be the same for all devices of the same type.
+    /// `broker` may be an IP address or a DNS name for the broker to connect to.
+    pub fn new(network: Stack<'t>, device_type: &'t str, broker: &'t str) -> Self {
+        Self {
+            network,
+            device_type,
+            broker,
+            device_id: None,
+            last_will: None,
+            username: None,
+            password: None,
+            subscriptions: [],
+        }
+    }
+}
+
+impl<'t, T: Deref<Target = str> + 't, L: Publishable + 't, const S: usize>
+    McutieBuilder<'t, T, L, S>
+{
+    /// Add some default topics to subscribe to.
+    pub fn with_subscriptions<const N: usize>(
+        self,
+        subscriptions: [Topic<T>; N],
+    ) -> McutieBuilder<'t, T, L, N> {
+        McutieBuilder {
+            network: self.network,
+            device_type: self.device_type,
+            broker: self.broker,
+            device_id: self.device_id,
+            last_will: self.last_will,
+            username: self.username,
+            password: self.password,
+            subscriptions,
+        }
+    }
+}
+
+impl<'t, T: Deref<Target = str> + 't, L: Publishable + 't, const S: usize>
+    McutieBuilder<'t, T, L, S>
+{
+    /// Adds authentication for the broker.
+    pub fn with_authentication(self, username: &'t str, password: &'t str) -> Self {
+        Self {
+            username: Some(username),
+            password: Some(password),
+            ..self
+        }
+    }
+
+    /// Sets a last will message to be published in the event of disconnection.
+    pub fn with_last_will(self, last_will: L) -> Self {
+        Self {
+            last_will: Some(last_will),
+            ..self
+        }
+    }
+
+    /// Sets a custom unique device identifier. If none is set then the network
+    /// MAC address is used.
+    pub fn with_device_id(self, device_id: &'t str) -> Self {
+        Self {
+            device_id: Some(device_id),
+            ..self
+        }
+    }
+
+    /// Initialises the MQTT stack returning a receiver for listening to
+    /// messages from the broker and a future that must be run in order for the
+    /// stack to operate.
+    pub fn build(self, keep_alive: u16) -> (McutieReceiver, McutieTask<'t, T, L, S>) {
+        let mut dtype = String::<32>::new();
+        dtype.push_str(self.device_type).unwrap();
+        DEVICE_TYPE.set(dtype).unwrap();
+
+        let mut did = String::<32>::new();
+        if let Some(device_id) = self.device_id {
+            did.push_str(device_id).unwrap();
+        } else if let HardwareAddress::Ethernet(address) = self.network.hardware_address() {
+            let mut buffer = [0_u8; 12];
+            hex::encode_to_slice(address.as_bytes(), &mut buffer).unwrap();
+            did.push_str(str::from_utf8(&buffer).unwrap()).unwrap();
+        }
+
+        DEVICE_ID.set(did).unwrap();
+
+        (
+            McutieReceiver {},
+            McutieTask {
+                network: self.network,
+                broker: self.broker,
+                last_will: self.last_will,
+                username: self.username,
+                password: self.password,
+                subscriptions: self.subscriptions,
+                keep_alive
+            },
+        )
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/pipe.rs

@@ -0,0 +1,267 @@
+use core::{
+    cell::RefCell,
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll, Waker},
+};
+
+use embassy_sync::blocking_mutex::{raw::RawMutex, Mutex};
+use pin_project::pin_project;
+
+struct PipeData<T, const N: usize> {
+    connect_count: usize,
+    receiver_waker: Option<Waker>,
+    sender_waker: Option<Waker>,
+    pending: Option<T>,
+}
+
+fn swap_wakers(waker: &mut Option<Waker>, new_waker: &Waker) {
+    if let Some(old_waker) = waker.take() {
+        if old_waker.will_wake(new_waker) {
+            *waker = Some(old_waker)
+        } else {
+            if !new_waker.will_wake(&old_waker) {
+                old_waker.wake();
+            }
+
+            *waker = Some(new_waker.clone());
+        }
+    } else {
+        *waker = Some(new_waker.clone())
+    }
+}
+
+pub(crate) struct ReceiveFuture<'a, M: RawMutex, T, const N: usize> {
+    pipe: &'a ConnectedPipe<M, T, N>,
+}
+
+impl<M: RawMutex, T, const N: usize> Future for ReceiveFuture<'_, M, T, N> {
+    type Output = T;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.pipe.inner.lock(|cell| {
+            let mut inner = cell.borrow_mut();
+
+            if let Some(waker) = inner.sender_waker.take() {
+                waker.wake();
+            }
+
+            if let Some(item) = inner.pending.take() {
+                if let Some(old_waker) = inner.receiver_waker.take() {
+                    old_waker.wake();
+                }
+
+                Poll::Ready(item)
+            } else {
+                swap_wakers(&mut inner.receiver_waker, cx.waker());
+                Poll::Pending
+            }
+        })
+    }
+}
+
+pub(crate) struct PipeReader<'a, M: RawMutex, T, const N: usize> {
+    pipe: &'a ConnectedPipe<M, T, N>,
+}
+
+impl<M: RawMutex, T, const N: usize> PipeReader<'_, M, T, N> {
+    #[must_use]
+    pub(crate) fn receive(&self) -> ReceiveFuture<'_, M, T, N> {
+        ReceiveFuture { pipe: self.pipe }
+    }
+}
+
+impl<M: RawMutex, T, const N: usize> Drop for PipeReader<'_, M, T, N> {
+    fn drop(&mut self) {
+        self.pipe.inner.lock(|cell| {
+            let mut inner = cell.borrow_mut();
+            inner.connect_count -= 1;
+
+            if inner.connect_count == 0 {
+                inner.pending = None;
+            }
+
+            if let Some(waker) = inner.sender_waker.take() {
+                waker.wake();
+            }
+        })
+    }
+}
+
+#[pin_project]
+pub(crate) struct PushFuture<'a, M: RawMutex, T, const N: usize> {
+    data: Option<T>,
+    pipe: &'a ConnectedPipe<M, T, N>,
+}
+
+impl<M: RawMutex, T, const N: usize> Future for PushFuture<'_, M, T, N> {
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.pipe.inner.lock(|cell| {
+            let project = self.project();
+            let mut inner = cell.borrow_mut();
+
+            if let Some(receiver) = inner.receiver_waker.take() {
+                receiver.wake();
+            }
+
+            if project.data.is_none() || inner.connect_count == 0 {
+                trace!("Dropping packet");
+                Poll::Ready(())
+            } else if inner.pending.is_some() {
+                swap_wakers(&mut inner.sender_waker, cx.waker());
+                Poll::Pending
+            } else {
+                inner.pending = project.data.take();
+
+                Poll::Ready(())
+            }
+        })
+    }
+}
+
+/// A pipe that knows whether a receiver is connected. If so pushing to the
+/// queue waits until there is space in the queue, otherwise data is simply
+/// dropped.
+pub(crate) struct ConnectedPipe<M: RawMutex, T, const N: usize> {
+    inner: Mutex<M, RefCell<PipeData<T, N>>>,
+}
+
+impl<M: RawMutex, T, const N: usize> ConnectedPipe<M, T, N> {
+    pub(crate) const fn new() -> Self {
+        Self {
+            inner: Mutex::new(RefCell::new(PipeData {
+                connect_count: 0,
+                receiver_waker: None,
+                sender_waker: None,
+                pending: None,
+            })),
+        }
+    }
+
+    /// A future that waits for a new item to be available.
+    pub(crate) fn reader(&self) -> PipeReader<'_, M, T, N> {
+        self.inner.lock(|cell| {
+            let mut inner = cell.borrow_mut();
+            inner.connect_count += 1;
+
+            PipeReader { pipe: self }
+        })
+    }
+
+    /// Pushes an item to the reader, waiting for a slot to become available if
+    /// connected.
+    #[must_use]
+    pub(crate) fn push(&self, data: T) -> PushFuture<'_, M, T, N> {
+        PushFuture {
+            data: Some(data),
+            pipe: self,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use core::time::Duration;
+
+    use embassy_sync::blocking_mutex::raw::CriticalSectionRawMutex;
+    use futures_executor::{LocalPool, ThreadPool};
+    use futures_timer::Delay;
+    use futures_util::{future::select, pin_mut, task::SpawnExt, FutureExt};
+
+    use super::ConnectedPipe;
+
+    async fn wait_milis(milis: u64) {
+        Delay::new(Duration::from_millis(milis)).await;
+    }
+
+    // #[futures_test::test]
+    #[test]
+    fn test_send_receive() {
+        let mut executor = LocalPool::new();
+        let spawner = executor.spawner();
+
+        static PIPE: ConnectedPipe<CriticalSectionRawMutex, usize, 5> = ConnectedPipe::new();
+
+        // Task that sends
+        spawner
+            .spawn(async {
+                wait_milis(10).await;
+
+                PIPE.push(23).await;
+                PIPE.push(56).await;
+                PIPE.push(67).await;
+            })
+            .unwrap();
+
+        // Task that receives
+        spawner
+            .spawn(async {
+                let reader = PIPE.reader();
+                let value = reader.receive().await;
+                assert_eq!(value, 23);
+                let value = reader.receive().await;
+                assert_eq!(value, 56);
+                let value = reader.receive().await;
+                assert_eq!(value, 67);
+            })
+            .unwrap();
+
+        executor.run();
+    }
+
+    #[futures_test::test]
+    async fn test_send_drop() {
+        static PIPE: ConnectedPipe<CriticalSectionRawMutex, usize, 5> = ConnectedPipe::new();
+
+        PIPE.push(23).await;
+        PIPE.push(56).await;
+        PIPE.push(67).await;
+
+        // Create a reader after sending
+        let reader = PIPE.reader();
+        let receive = reader.receive().fuse();
+        pin_mut!(receive);
+
+        let timeout = wait_milis(50).fuse();
+        pin_mut!(timeout);
+
+        let either = select(receive, timeout).await;
+
+        match either {
+            futures_util::future::Either::Left(_) => {
+                panic!("There should be nothing to receive!");
+            }
+            futures_util::future::Either::Right(_) => {}
+        }
+    }
+
+    #[futures_test::test]
+    async fn test_bulk_send_publish() {
+        static PIPE: ConnectedPipe<CriticalSectionRawMutex, usize, 5> = ConnectedPipe::new();
+
+        let executor = ThreadPool::new().unwrap();
+
+        executor
+            .spawn(async {
+                for i in 0..1000 {
+                    PIPE.push(i).await;
+                }
+            })
+            .unwrap();
+
+        executor
+            .spawn(async {
+                for i in 1000..2000 {
+                    PIPE.push(i).await;
+                }
+            })
+            .unwrap();
+
+        let reader = PIPE.reader();
+        for _ in 0..800 {
+            reader.receive().await;
+        }
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/publish.rs

@@ -0,0 +1,173 @@
+use core::{fmt::Display, future::Future, ops::Deref};
+
+use embedded_io::Write;
+use mqttrs::QoS;
+
+use crate::{io::publish, Error, Payload, Topic, TopicString};
+
+/// A message that can be published to an MQTT broker.
+pub trait Publishable {
+    /// Write this message's topic into the supplied buffer.
+    fn write_topic(&self, buffer: &mut TopicString) -> Result<(), Error>;
+
+    /// Write this message's payload into the supplied buffer.
+    fn write_payload(&self, buffer: &mut Payload) -> Result<(), Error>;
+
+    /// Get this message's QoS level.
+    fn qos(&self) -> QoS {
+        QoS::AtMostOnce
+    }
+
+    /// Whether the broker should retain this message.
+    fn retain(&self) -> bool {
+        false
+    }
+
+    /// Publishes this message to the broker. If the stack has not yet been
+    /// initialized this is likely to panic.
+    fn publish(&self) -> impl Future<Output = Result<(), Error>> {
+        async {
+            let mut topic = TopicString::new();
+            self.write_topic(&mut topic)?;
+
+            let mut payload = Payload::new();
+            self.write_payload(&mut payload)?;
+
+            publish(&topic, &payload, self.qos(), self.retain()).await
+        }
+    }
+}
+
+/// A [`Publishable`] with a raw byte payload.
+pub struct PublishBytes<'a, T, B: AsRef<[u8]>> {
+    pub(crate) topic: &'a Topic<T>,
+    pub(crate) data: B,
+    pub(crate) qos: QoS,
+    pub(crate) retain: bool,
+}
+
+impl<T, B: AsRef<[u8]>> PublishBytes<'_, T, B> {
+    /// Sets the QoS level for this message.
+    pub fn qos(mut self, qos: QoS) -> Self {
+        self.qos = qos;
+        self
+    }
+
+    /// Sets whether the broker should retain this message.
+    pub fn retain(mut self, retain: bool) -> Self {
+        self.retain = retain;
+        self
+    }
+}
+
+impl<'a, T: Deref<Target = str> + 'a, B: AsRef<[u8]>> Publishable for PublishBytes<'a, T, B> {
+    fn write_topic(&self, buffer: &mut TopicString) -> Result<(), Error> {
+        self.topic.to_string(buffer)
+    }
+
+    fn write_payload(&self, buffer: &mut Payload) -> Result<(), Error> {
+        buffer
+            .write_all(self.data.as_ref())
+            .map_err(|_| Error::TooLarge)
+    }
+
+    fn qos(&self) -> QoS {
+        self.qos
+    }
+
+    fn retain(&self) -> bool {
+        self.retain
+    }
+
+    async fn publish(&self) -> Result<(), Error> {
+        let mut topic = TopicString::new();
+        self.write_topic(&mut topic)?;
+
+        publish(&topic, self.data.as_ref(), self.qos(), self.retain()).await
+    }
+}
+
+/// A [`Publishable`] with a payload that implements [`Display`].
+pub struct PublishDisplay<'a, T, D: Display> {
+    pub(crate) topic: &'a Topic<T>,
+    pub(crate) data: D,
+    pub(crate) qos: QoS,
+    pub(crate) retain: bool,
+}
+
+impl<T, D: Display> PublishDisplay<'_, T, D> {
+    /// Sets the QoS level for this message.
+    pub fn qos(mut self, qos: QoS) -> Self {
+        self.qos = qos;
+        self
+    }
+
+    /// Sets whether the broker should retain this message.
+    pub fn retain(mut self, retain: bool) -> Self {
+        self.retain = retain;
+        self
+    }
+}
+
+impl<'a, T: Deref<Target = str> + 'a, D: Display> Publishable for PublishDisplay<'a, T, D> {
+    fn write_topic(&self, buffer: &mut TopicString) -> Result<(), Error> {
+        self.topic.to_string(buffer)
+    }
+
+    fn write_payload(&self, buffer: &mut Payload) -> Result<(), Error> {
+        write!(buffer, "{}", self.data).map_err(|_| Error::TooLarge)
+    }
+
+    fn qos(&self) -> QoS {
+        self.qos
+    }
+
+    fn retain(&self) -> bool {
+        self.retain
+    }
+}
+
+#[cfg(feature = "serde")]
+/// A [`Publishable`] with that serializes a JSON payload.
+pub struct PublishJson<'a, T, D: serde::Serialize> {
+    pub(crate) topic: &'a Topic<T>,
+    pub(crate) data: D,
+    pub(crate) qos: QoS,
+    pub(crate) retain: bool,
+}
+
+#[cfg(feature = "serde")]
+impl<T, D: serde::Serialize> PublishJson<'_, T, D> {
+    /// Sets the QoS level for this message.
+    pub fn qos(mut self, qos: QoS) -> Self {
+        self.qos = qos;
+        self
+    }
+
+    /// Sets whether the broker should retain this message.
+    pub fn retain(mut self, retain: bool) -> Self {
+        self.retain = retain;
+        self
+    }
+}
+
+#[cfg(feature = "serde")]
+impl<'a, T: Deref<Target = str> + 'a, D: serde::Serialize> Publishable for PublishJson<'a, T, D> {
+    fn write_topic(&self, buffer: &mut TopicString) -> Result<(), Error> {
+        self.topic.to_string(buffer)
+    }
+
+    fn write_payload(&self, buffer: &mut Payload) -> Result<(), Error> {
+        buffer
+            .serialize_json(&self.data)
+            .map_err(|_| Error::TooLarge)
+    }
+
+    fn qos(&self) -> QoS {
+        self.qos
+    }
+
+    fn retain(&self) -> bool {
+        self.retain
+    }
+}

Software/MainBoard/rust/src/mcutie_3_0_0/topic.rs

@@ -0,0 +1,284 @@
+use core::{fmt::Display, ops::Deref};
+
+use embassy_futures::select::{select, Either};
+use embassy_sync::pubsub::WaitResult;
+use embassy_time::Timer;
+use heapless::{String, Vec};
+use mqttrs::{Packet, QoS, Subscribe, SubscribeReturnCodes, SubscribeTopic, Unsubscribe};
+
+#[cfg(feature = "serde")]
+use crate::publish::PublishJson;
+use crate::{
+    device_id, device_type,
+    io::{assign_pid, send_packet, subscribe},
+    publish::{PublishBytes, PublishDisplay},
+    ControlMessage, Error, TopicString, CONFIRMATION_TIMEOUT,
+};
+
+/// An MQTT topic that is optionally prefixed with the device type and unique ID.
+/// Normally you will define all your application's topics as consts with static
+/// lifetimes.
+///
+/// A [`Topic`] is the main entry to publishing messages to the broker.
+///
+/// ```
+/// # use mcutie::{Publishable, Topic};
+/// const DEVICE_AVAILABILITY: Topic<&'static str> = Topic::Device("state");
+///
+/// async fn send_status(status: &'static str) {
+///   let _ = DEVICE_AVAILABILITY.with_bytes(status.as_bytes()).publish().await;
+/// }
+/// ```
+#[derive(Clone, Copy)]
+pub enum Topic<T> {
+    /// A topic that is prefixed with the device type.
+    DeviceType(T),
+    /// A topic that is prefixed with the device type and unique ID.
+    Device(T),
+    /// Any topic.
+    General(T),
+}
+
+impl<A, B> PartialEq<Topic<A>> for Topic<B>
+where
+    B: PartialEq<A>,
+{
+    fn eq(&self, other: &Topic<A>) -> bool {
+        match (self, other) {
+            (Topic::DeviceType(l0), Topic::DeviceType(r0)) => l0 == r0,
+            (Topic::Device(l0), Topic::Device(r0)) => l0 == r0,
+            (Topic::General(l0), Topic::General(r0)) => l0 == r0,
+            _ => false,
+        }
+    }
+}
+
+impl<T> Topic<T> {
+    /// Creates a publishable message with something that can return a reference
+    /// to the payload in bytes.
+    ///
+    /// Defaults to non-retained with QoS of 0 (AtMostOnce).
+    pub fn with_bytes<B: AsRef<[u8]>>(&self, data: B) -> PublishBytes<'_, T, B> {
+        PublishBytes {
+            topic: self,
+            data,
+            qos: QoS::AtMostOnce,
+            retain: false,
+        }
+    }
+
+    /// Creates a publishable message with something that implements [`Display`].
+    ///
+    /// Defaults to non-retained with QoS of 0 (AtMostOnce).
+    pub fn with_display<D: Display>(&self, data: D) -> PublishDisplay<'_, T, D> {
+        PublishDisplay {
+            topic: self,
+            data,
+            qos: QoS::AtMostOnce,
+            retain: false,
+        }
+    }
+
+    #[cfg(feature = "serde")]
+    /// Creates a publishable message with something that can be serialized to
+    /// JSON.
+    ///
+    /// Defaults to non-retained with QoS of 0 (AtMostOnce).
+    pub fn with_json<D: serde::Serialize>(&self, data: D) -> PublishJson<'_, T, D> {
+        PublishJson {
+            topic: self,
+            data,
+            qos: QoS::AtMostOnce,
+            retain: false,
+        }
+    }
+}
+
+impl Topic<TopicString> {
+    pub(crate) fn from_str(mut st: &str) -> Result<Self, Error> {
+        let mut strip_prefix = |pr: &str| -> bool {
+            if st.starts_with(pr) && st.len() > pr.len() && &st[pr.len()..pr.len() + 1] == "/" {
+                st = &st[pr.len() + 1..];
+                true
+            } else {
+                false
+            }
+        };
+
+        if strip_prefix(device_type()) {
+            if strip_prefix(device_id()) {
+                let mut topic = TopicString::new();
+                topic.push_str(st).map_err(|_| Error::TooLarge)?;
+                Ok(Topic::Device(topic))
+            } else {
+                let mut topic = TopicString::new();
+                topic.push_str(st).map_err(|_| Error::TooLarge)?;
+                Ok(Topic::DeviceType(topic))
+            }
+        } else {
+            let mut topic = TopicString::new();
+            topic.push_str(st).map_err(|_| Error::TooLarge)?;
+            Ok(Topic::General(topic))
+        }
+    }
+}
+
+impl<T: Deref<Target = str>> Topic<T> {
+    pub(crate) fn to_string<const N: usize>(&self, result: &mut String<N>) -> Result<(), Error> {
+        match self {
+            Topic::Device(st) => {
+                result
+                    .push_str(device_type())
+                    .map_err(|_| Error::TooLarge)?;
+                result.push_str("/").map_err(|_| Error::TooLarge)?;
+                result.push_str(device_id()).map_err(|_| Error::TooLarge)?;
+                result.push_str("/").map_err(|_| Error::TooLarge)?;
+                result.push_str(st.as_ref()).map_err(|_| Error::TooLarge)?;
+            }
+            Topic::DeviceType(st) => {
+                result
+                    .push_str(device_type())
+                    .map_err(|_| Error::TooLarge)?;
+                result.push_str("/").map_err(|_| Error::TooLarge)?;
+                result.push_str(st.as_ref()).map_err(|_| Error::TooLarge)?;
+            }
+            Topic::General(st) => {
+                result.push_str(st.as_ref()).map_err(|_| Error::TooLarge)?;
+            }
+        }
+
+        Ok(())
+    }
+
+    /// Converts to a topic containing an [`str`]. Particularly useful for converting from an owned
+    /// string for match patterns.
+    pub fn as_ref(&self) -> Topic<&str> {
+        match self {
+            Topic::DeviceType(st) => Topic::DeviceType(st.as_ref()),
+            Topic::Device(st) => Topic::Device(st.as_ref()),
+            Topic::General(st) => Topic::General(st.as_ref()),
+        }
+    }
+
+    /// Subscribes to this topic. If `wait_for_ack` is true then this will wait until confirmation
+    /// is received from the broker before returning.
+    pub async fn subscribe(&self, wait_for_ack: bool) -> Result<(), Error> {
+        let mut subscriber = subscribe().await;
+
+        let mut topic_path = TopicString::new();
+        if self.to_string(&mut topic_path).is_err() {
+            return Err(Error::TooLarge);
+        }
+
+        let pid = assign_pid().await;
+
+        let mut subscribe_topic_path = String::<256>::new();
+        subscribe_topic_path
+            .push_str(topic_path.as_str())
+            .map_err(|_| Error::TooLarge)?;
+        let subscribe_topic = SubscribeTopic {
+            topic_path: subscribe_topic_path,
+            qos: QoS::AtLeastOnce,
+        };
+
+        // The size of this vec must match that used by mqttrs.
+        let topics = match Vec::<SubscribeTopic, 5>::from_slice(&[subscribe_topic]) {
+            Ok(t) => t,
+            Err(_) => return Err(Error::TooLarge),
+        };
+
+        let packet = Packet::Subscribe(Subscribe { pid, topics });
+
+        send_packet(packet).await?;
+
+        if wait_for_ack {
+            match select(
+                async {
+                    loop {
+                        match subscriber.next_message().await {
+                            WaitResult::Lagged(_) => {
+                                // Maybe we missed the message?
+                            }
+                            WaitResult::Message(ControlMessage::Subscribed(
+                                subscribed_pid,
+                                return_code,
+                            )) => {
+                                if subscribed_pid == pid {
+                                    if matches!(return_code, SubscribeReturnCodes::Success(_)) {
+                                        return Ok(());
+                                    } else {
+                                        return Err(Error::IOError);
+                                    }
+                                }
+                            }
+                            _ => {}
+                        }
+                    }
+                },
+                Timer::after_millis(CONFIRMATION_TIMEOUT),
+            )
+            .await
+            {
+                Either::First(r) => r,
+                Either::Second(_) => Err(Error::TimedOut),
+            }
+        } else {
+            Ok(())
+        }
+    }
+
+    /// Unsubscribes from a topic. If `wait_for_ack` is true then this will wait until confirmation is
+    /// received from the broker before returning.
+    pub async fn unsubscribe(&self, wait_for_ack: bool) -> Result<(), Error> {
+        let mut subscriber = subscribe().await;
+
+        let mut topic_path = TopicString::new();
+        if self.to_string(&mut topic_path).is_err() {
+            return Err(Error::TooLarge);
+        }
+
+        let pid = assign_pid().await;
+
+        // The size of this vec must match that used by mqttrs.
+        let mut unsubscribe_topic_path = String::<256>::new();
+        unsubscribe_topic_path
+            .push_str(topic_path.as_str())
+            .map_err(|_| Error::TooLarge)?;
+        let topics = match Vec::<String<256>, 5>::from_slice(&[unsubscribe_topic_path]) {
+            Ok(t) => t,
+            Err(_) => return Err(Error::TooLarge),
+        };
+
+        let packet = Packet::Unsubscribe(Unsubscribe { pid, topics });
+
+        send_packet(packet).await?;
+
+        if wait_for_ack {
+            match select(
+                async {
+                    loop {
+                        match subscriber.next_message().await {
+                            WaitResult::Lagged(_) => {
+                                // Maybe we missed the message?
+                            }
+                            WaitResult::Message(ControlMessage::Unsubscribed(subscribed_pid)) => {
+                                if subscribed_pid == pid {
+                                    return Ok(());
+                                }
+                            }
+                            _ => {}
+                        }
+                    }
+                },
+                Timer::after_millis(CONFIRMATION_TIMEOUT),
+            )
+            .await
+            {
+                Either::First(r) => r,
+                Either::Second(_) => Err(Error::TimedOut),
+            }
+        } else {
+            Ok(())
+        }
+    }
+}