Make IEC 62056-21 meter input non-blocking

- Add RX state machine with frame buffer, timeouts, and debug counters

- Expose meter_poll_frame/meter_parse_frame and reuse existing OBIS parsing

- Use cached last-valid frame at 1 Hz sampling to avoid blocking

- Document non-blocking meter handling in README

README.md

@@ -54,6 +54,7 @@ Variants:
   - Energy total: 1-0:1.8.0*255
   - Total power: 1-0:16.7.0*255
   - Phase power: 36.7 / 56.7 / 76.7
+- Meter input is parsed via a non-blocking RX state machine; the last valid frame is reused for 1 Hz sampling.
 - Reads battery voltage and estimates SoC.
 - Builds compact binary batch payload, wraps in LoRa packet, transmits.
 - Light sleeps between meter reads; batches are sent every 30s.

include/meter_driver.h

@@ -5,3 +5,5 @@
 
 void meter_init();
 bool meter_read(MeterData &data);
+bool meter_poll_frame(const char *&frame, size_t &len);
+bool meter_parse_frame(const char *frame, size_t len, MeterData &data);

src/main.cpp

@@ -92,6 +92,10 @@ static uint32_t g_sender_last_timesync_check_ms = 0;
 static uint32_t g_sender_rx_window_ms = 0;
 static uint32_t g_sender_sleep_ms = 0;
 static uint32_t g_sender_power_log_ms = 0;
+static MeterData g_last_meter_data = {};
+static bool g_last_meter_valid = false;
+static uint32_t g_last_meter_rx_ms = 0;
+static uint32_t g_meter_stale_seconds = 0;
 
 static void watchdog_kick();
 
@@ -696,13 +700,42 @@ static void sender_loop() {
                         g_batch_retry_count);
   }
 
+  const char *frame = nullptr;
+  size_t frame_len = 0;
+  if (meter_poll_frame(frame, frame_len)) {
+    MeterData parsed = {};
+    parsed.energy_total_kwh = NAN;
+    parsed.total_power_w = NAN;
+    parsed.phase_power_w[0] = NAN;
+    parsed.phase_power_w[1] = NAN;
+    parsed.phase_power_w[2] = NAN;
+    parsed.valid = false;
+    if (meter_parse_frame(frame, frame_len, parsed)) {
+      g_last_meter_data = parsed;
+      g_last_meter_valid = true;
+      g_last_meter_rx_ms = now_ms;
+      g_meter_stale_seconds = 0;
+    }
+  }
+
   if (now_ms - g_last_sample_ms >= METER_SAMPLE_INTERVAL_MS) {
     g_last_sample_ms = now_ms;
     MeterData data = {};
     data.short_id = g_short_id;
     strncpy(data.device_id, g_device_id, sizeof(data.device_id));
 
-    bool meter_ok = meter_read(data);
+    bool meter_ok = g_last_meter_valid;
+    if (meter_ok) {
+      data.energy_total_kwh = g_last_meter_data.energy_total_kwh;
+      data.total_power_w = g_last_meter_data.total_power_w;
+      data.phase_power_w[0] = g_last_meter_data.phase_power_w[0];
+      data.phase_power_w[1] = g_last_meter_data.phase_power_w[1];
+      data.phase_power_w[2] = g_last_meter_data.phase_power_w[2];
+      uint32_t age_ms = now_ms - g_last_meter_rx_ms;
+      g_meter_stale_seconds = age_ms >= 1000 ? (age_ms / 1000) : 0;
+    } else {
+      g_meter_stale_seconds++;
+    }
     if (!meter_ok) {
       note_fault(g_sender_faults, g_sender_last_error, g_sender_last_error_utc, g_sender_last_error_ms, FaultType::MeterRead);
       display_set_last_error(g_sender_last_error, g_sender_last_error_utc, g_sender_last_error_ms);

src/meter_driver.cpp

@@ -4,7 +4,24 @@
 #include <stdlib.h>
 #include <string.h>
 
-static constexpr uint32_t METER_READ_TIMEOUT_MS = 2000;
+static constexpr uint32_t METER_FRAME_TIMEOUT_MS = 1500;
+static constexpr size_t METER_FRAME_MAX = 512;
+
+enum class MeterRxState : uint8_t {
+  WaitStart = 0,
+  InFrame = 1
+};
+
+static MeterRxState g_rx_state = MeterRxState::WaitStart;
+static char g_frame_buf[METER_FRAME_MAX + 1];
+static size_t g_frame_len = 0;
+static uint32_t g_last_rx_ms = 0;
+static uint32_t g_bytes_rx = 0;
+static uint32_t g_frames_ok = 0;
+static uint32_t g_frames_parse_fail = 0;
+static uint32_t g_rx_overflow = 0;
+static uint32_t g_rx_timeout = 0;
+static uint32_t g_last_log_ms = 0;
 
 void meter_init() {
   Serial2.begin(9600, SERIAL_7E1, PIN_METER_RX, -1);
@@ -77,11 +94,76 @@ static bool parse_obis_ascii_unit_scale(const char *line, const char *obis, floa
   return false;
 }
 
-static bool meter_read_ascii(MeterData &data) {
-  const uint32_t start_ms = millis();
-  bool in_telegram = false;
-  bool got_any = false;
+static void meter_debug_log() {
+  if (!SERIAL_DEBUG_MODE) {
+    return;
+  }
+  uint32_t now_ms = millis();
+  if (now_ms - g_last_log_ms < 60000) {
+    return;
+  }
+  g_last_log_ms = now_ms;
+  Serial.printf("meter: ok=%lu parse_fail=%lu overflow=%lu timeout=%lu bytes=%lu\n",
+                static_cast<unsigned long>(g_frames_ok),
+                static_cast<unsigned long>(g_frames_parse_fail),
+                static_cast<unsigned long>(g_rx_overflow),
+                static_cast<unsigned long>(g_rx_timeout),
+                static_cast<unsigned long>(g_bytes_rx));
+}
 
+bool meter_poll_frame(const char *&frame, size_t &len) {
+  frame = nullptr;
+  len = 0;
+  uint32_t now_ms = millis();
+
+  if (g_rx_state == MeterRxState::InFrame && (now_ms - g_last_rx_ms > METER_FRAME_TIMEOUT_MS)) {
+    g_rx_timeout++;
+    g_rx_state = MeterRxState::WaitStart;
+    g_frame_len = 0;
+  }
+
+  while (Serial2.available()) {
+    char c = static_cast<char>(Serial2.read());
+    g_bytes_rx++;
+    g_last_rx_ms = now_ms;
+
+    if (g_rx_state == MeterRxState::WaitStart) {
+      if (c == '/') {
+        g_rx_state = MeterRxState::InFrame;
+        g_frame_len = 0;
+        g_frame_buf[g_frame_len++] = c;
+      }
+      continue;
+    }
+
+    if (g_frame_len + 1 >= sizeof(g_frame_buf)) {
+      g_rx_overflow++;
+      g_rx_state = MeterRxState::WaitStart;
+      g_frame_len = 0;
+      continue;
+    }
+
+    g_frame_buf[g_frame_len++] = c;
+    if (c == '!') {
+      g_frame_buf[g_frame_len] = '\0';
+      frame = g_frame_buf;
+      len = g_frame_len;
+      g_rx_state = MeterRxState::WaitStart;
+      g_frame_len = 0;
+      meter_debug_log();
+      return true;
+    }
+  }
+
+  meter_debug_log();
+  return false;
+}
+
+bool meter_parse_frame(const char *frame, size_t len, MeterData &data) {
+  if (!frame || len == 0) {
+    return false;
+  }
+  bool got_any = false;
   bool energy_ok = false;
   bool total_p_ok = false;
   bool p1_ok = false;
@@ -90,66 +172,78 @@ static bool meter_read_ascii(MeterData &data) {
   char line[128];
   size_t line_len = 0;
 
-  while (millis() - start_ms < METER_READ_TIMEOUT_MS) {
-    while (Serial2.available()) {
-      char c = static_cast<char>(Serial2.read());
-      if (!in_telegram) {
-        if (c == '/') {
-          in_telegram = true;
-          line_len = 0;
-          line[line_len++] = c;
-        }
-        continue;
-      }
-
-      if (c == '\r') {
-        continue;
-      }
-      if (c == '\n') {
-        line[line_len] = '\0';
-        if (line[0] == '!') {
-          return got_any;
-        }
-
-        float value = NAN;
-        if (parse_obis_ascii_value(line, "1-0:1.8.0", value)) {
-          parse_obis_ascii_unit_scale(line, "1-0:1.8.0", value);
-          data.energy_total_kwh = value;
-          energy_ok = true;
-          got_any = true;
-        }
-        if (parse_obis_ascii_value(line, "1-0:16.7.0", value)) {
-          data.total_power_w = value;
-          total_p_ok = true;
-          got_any = true;
-        }
-        if (parse_obis_ascii_value(line, "1-0:36.7.0", value)) {
-          data.phase_power_w[0] = value;
-          p1_ok = true;
-          got_any = true;
-        }
-        if (parse_obis_ascii_value(line, "1-0:56.7.0", value)) {
-          data.phase_power_w[1] = value;
-          p2_ok = true;
-          got_any = true;
-        }
-        if (parse_obis_ascii_value(line, "1-0:76.7.0", value)) {
-          data.phase_power_w[2] = value;
-          p3_ok = true;
-          got_any = true;
-        }
-
-        line_len = 0;
-        continue;
-      }
+  for (size_t i = 0; i < len; ++i) {
+    char c = frame[i];
+    if (c == '\r') {
+      continue;
+    }
+    if (c == '!') {
       if (line_len + 1 < sizeof(line)) {
         line[line_len++] = c;
       }
+      line[line_len] = '\0';
+      data.valid = energy_ok || total_p_ok || p1_ok || p2_ok || p3_ok;
+      if (data.valid) {
+        g_frames_ok++;
+      } else {
+        g_frames_parse_fail++;
+      }
+      return data.valid;
+    }
+    if (c == '\n') {
+      line[line_len] = '\0';
+      if (line[0] == '!') {
+        data.valid = energy_ok || total_p_ok || p1_ok || p2_ok || p3_ok;
+        if (data.valid) {
+          g_frames_ok++;
+        } else {
+          g_frames_parse_fail++;
+        }
+        return data.valid;
+      }
+
+      float value = NAN;
+      if (parse_obis_ascii_value(line, "1-0:1.8.0", value)) {
+        parse_obis_ascii_unit_scale(line, "1-0:1.8.0", value);
+        data.energy_total_kwh = value;
+        energy_ok = true;
+        got_any = true;
+      }
+      if (parse_obis_ascii_value(line, "1-0:16.7.0", value)) {
+        data.total_power_w = value;
+        total_p_ok = true;
+        got_any = true;
+      }
+      if (parse_obis_ascii_value(line, "1-0:36.7.0", value)) {
+        data.phase_power_w[0] = value;
+        p1_ok = true;
+        got_any = true;
+      }
+      if (parse_obis_ascii_value(line, "1-0:56.7.0", value)) {
+        data.phase_power_w[1] = value;
+        p2_ok = true;
+        got_any = true;
+      }
+      if (parse_obis_ascii_value(line, "1-0:76.7.0", value)) {
+        data.phase_power_w[2] = value;
+        p3_ok = true;
+        got_any = true;
+      }
+
+      line_len = 0;
+      continue;
+    }
+    if (line_len + 1 < sizeof(line)) {
+      line[line_len++] = c;
     }
-    delay(5);
   }
 
-  data.valid = energy_ok || total_p_ok || p1_ok || p2_ok || p3_ok;
+  data.valid = got_any;
+  if (data.valid) {
+    g_frames_ok++;
+  } else {
+    g_frames_parse_fail++;
+  }
   return data.valid;
 }
 
@@ -161,5 +255,10 @@ bool meter_read(MeterData &data) {
   data.phase_power_w[2] = NAN;
   data.valid = false;
 
-  return meter_read_ascii(data);
+  const char *frame = nullptr;
+  size_t len = 0;
+  if (!meter_poll_frame(frame, len)) {
+    return false;
+  }
+  return meter_parse_frame(frame, len, data);
 }