DD3-LoRa-Bridge-MultiSender/README.md

# DD3-LoRa-Bridge-MultiSender

Firmware for LilyGO T3 v1.6.1 (`ESP32 + SX1276 + SSD1306`) that runs in two roles:
- `Sender` (`GPIO14` HIGH): reads one IEC 62056-21 meter, builds 30-slot sparse batches, sends via LoRa.
- `Receiver` (`GPIO14` LOW): receives/ACKs batches, publishes MQTT, serves web UI, logs to SD.

## Architecture Summary

- Single codebase, role selected at boot by `detect_role()` (`src/config.cpp`).
- LoRa transport is wrapped with firmware-level CRC16-CCITT (`src/lora_transport.cpp`).
- Sender meter ingest is decoupled from LoRa waits via FreeRTOS meter reader task + queue on ESP32 (`src/main.cpp`).
- Batch payload codec is schema `v3` with a 30-bit `present_mask` over `[t_last-29, t_last]` (`src/payload_codec.cpp`).
- Sender only starts normal metering/transmit flow after valid time bootstrap from receiver ACK.
- Receiver runs STA mode if stored config is valid and connects, otherwise AP fallback.

## LoRa Protocol

On-air frame:

`[msg_kind:1][device_short_id:2][payload...][crc16:2]`

`msg_kind`:
- `0`: `BatchUp`
- `1`: `AckDown`

### BatchUp

Transport layer chunks payload into:

`[batch_id_le:2][chunk_index:1][chunk_count:1][total_len_le:2][chunk_payload...]`

Receiver reassembles all chunks before decode.

Payload codec (`schema=3`, magic `0xDDB3`) carries:
- metadata: sender ID, batch ID, `t_last`, `present_mask`, battery mV, error counters
- arrays per present sample: `energy_wh[]`, `p1_w[]`, `p2_w[]`, `p3_w[]`

`n == 0` with `present_mask == 0` is valid and used for sync request packets.

### AckDown (7 bytes payload)

`[flags:1][batch_id_be:2][epoch_utc_be:4]`

- `flags bit0`: `time_valid`
- ACK is repeated (`ACK_REPEAT_COUNT=3`, `ACK_REPEAT_DELAY_MS=200`)
- Sender sets local time only if `time_valid=1` and `epoch >= MIN_ACCEPTED_EPOCH_UTC` (`2026-02-01 00:00:00 UTC`)

## Time Bootstrap and Timezone

Sender boot starts in sync-only mode:
- `g_time_acquired=false`
- sends sync requests every `SYNC_REQUEST_INTERVAL_MS` (`15s`)
- does not run normal 1 Hz sample/batch flow yet

After valid ACK time:
- `time_set_utc()` is called
- `g_time_acquired=true`
- normal 1 Hz sampling + periodic batch transmission starts

Timezone:
- `TIMEZONE_TZ` from `include/config.h` is applied in `time_manager`.
- Web/OLED local-time rendering uses this timezone.
- Default: `CET-1CEST,M3.5.0/2,M10.5.0/3`.

## Sender Meter Path

Implemented by `src/meter_driver.cpp` and sender loop in `src/main.cpp`:
- UART: `Serial2`, `GPIO34`, `9600 7E1`
- ESP32 RX buffer enlarged to `8192`
- Frame detection `/ ... !`, timeout `METER_FRAME_TIMEOUT_MS=3000`
- Parsed OBIS fields:
  - `0-0:96.8.0*255` meter Sekundenindex (hex u32)
  - `1-0:1.8.0` total energy (auto scales Wh -> kWh when unit is Wh)
  - `1-0:16.7.0` total active power
  - `1-0:36.7.0`, `56.7.0`, `76.7.0` phase powers

Timestamp derivation:
- anchor offset: `epoch_offset = epoch_now - meter_seconds`
- sample epoch: `ts_utc = meter_seconds + epoch_offset`
- jump checks: rollback, wall-time delta mismatch, anchor drift

Sender builds sparse 30-slot windows and sends every `METER_SEND_INTERVAL_MS` (`30s`).

## Receiver Behavior

For decoded `BatchUp`:
1. Reassemble and decode.
2. Send `AckDown` immediately.
3. Track duplicates per configured sender (`EXPECTED_SENDER_IDS`).
4. If duplicate: update duplicate counters/time, skip data write/publish.
5. If `n==0`: sync request path only.
6. Else reconstruct each sample timestamp from `t_last + present_mask`, then:
   - append to SD CSV
   - publish MQTT state
   - update web status and last batch table

## MQTT

State topic:
- `smartmeter/<device_id>/state`

Fault topic (retained):
- `smartmeter/<device_id>/faults`

State JSON (`src/json_codec.cpp`) includes:
- `id`, `ts`, `e_kwh`
- `p_w`, `p1_w`, `p2_w`, `p3_w`
- `bat_v`, `bat_pct`
- optional link: `rssi`, `snr`
- `err_last`, `rx_reject`, `rx_reject_text`
- non-zero fault counters when available

Home Assistant discovery:
- enabled by `ENABLE_HA_DISCOVERY=true`
- publishes to `homeassistant/sensor/<device_id>/<key>/config`

## Web UI, Wi-Fi, SD

- Wi-Fi/MQTT/NTP/web-auth config is stored in Preferences.
- AP fallback SSID prefix: `DD3-Bridge-`.
- Default web credentials: `admin/admin`.
- AP auth requirement is controlled by `WEB_AUTH_REQUIRE_AP` (default `false`).
- STA auth requirement is controlled by `WEB_AUTH_REQUIRE_STA` (default `true`).

Web timestamp display:
- human-facing timestamps show `epoch (HH:MM:SS TZ)` in local configured timezone.

SD CSV logging (`src/sd_logger.cpp`):
- header: `ts_utc,ts_hms_utc,p_w,p1_w,p2_w,p3_w,e_kwh,bat_v,bat_pct,rssi,snr,err_m,err_d,err_tx,err_last`
- `ts_hms_utc` is UTC `HH:MM:SS`

History parser (`src/web_server.cpp`):
- expects the current CSV layout above
- legacy CSV layouts are not parsed (no backward compatibility)

OLED duplicate display:
- receiver sender-pages show duplicate rate as `pct (absolute)` and last duplicate as `HH:MM`.

## Build Environments

From `platformio.ini`:
- `lilygo-t3-v1-6-1`
- `lilygo-t3-v1-6-1-test`
- `lilygo-t3-v1-6-1-868`
- `lilygo-t3-v1-6-1-868-test`
- `lilygo-t3-v1-6-1-payload-test`
- `lilygo-t3-v1-6-1-868-payload-test`
- `lilygo-t3-v1-6-1-prod`
- `lilygo-t3-v1-6-1-868-prod`

Example:

```bash
python -m platformio run -e lilygo-t3-v1-6-1
```

## Test Mode

`ENABLE_TEST_MODE` replaces normal loops with `test_sender_loop` / `test_receiver_loop` (`src/test_mode.cpp`):
- Sender emits periodic JSON test payloads over LoRa.
- Receiver decodes test payloads, updates display test codes, publishes MQTT to:
  - `smartmeter/<device_id>/test`