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onju-v2/m5_echo/README.md
justLV 04990145ae Embed git hash in m5_echo, generate git_hash.h in flash.sh 
Moves git_hash.h generation from the one-shot setup-git-hash.sh
post-commit hook into flash.sh, so fresh checkouts don't need a
bootstrap step. Only rewrites the file when the hash changes to
avoid triggering unnecessary recompiles.

Also wires GIT_HASH into m5_echo: startup log, multicast announce,
and the Device: line. Both sketches now append the hash to Device:.
2026-04-12 14:18:21 -07:00

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M5 Echo - Push-to-Talk Voice Client

Firmware for the M5Stack ATOM Echo that connects to the pipeline server using the same protocol as onjuino, but with push-to-talk (PTT) instead of voice-activity detection (VAD).

How it differs from onjuino

onjuino m5_echo
Board ESP32-S3 (custom PCB) ESP32-PICO-D4 (M5Stack ATOM Echo)
Mic Standard I2S (separate ADC) PDM (SPM1423, on-chip)
Speaker MAX98357A, 6 NeoPixel LEDs NS4168, 1 SK6812 LED
Interaction Capacitive touch: tap to wake, VAD detects end of speech Physical button: hold to talk, release to listen
Mic control VAD-driven (server detects silence and processes) Push-to-talk only - mic active while button held
Call lifecycle Tap to activate, VAD handles turn-taking Auto-starts on boot, persistent until server disconnects
PSRAM Yes (2MB, large playback buffer) No (smaller buffers, more DMA buffers to compensate)
Opus Full encoder + decoder Decoder only (mic sends mu-law)
I2S Single config for simultaneous TX+RX Switches between PDM RX (mic) and I2S TX (speaker)

PTT behavior

  • Boot: Connects to WiFi, announces on multicast with PTT flag. Server auto-starts a call and opens a persistent TCP connection.
  • Idle: Server streams Opus audio over the persistent TCP connection. Device decodes and plays through the speaker.
  • Button press: Immediately stops speaker playback (I2S switches to PDM mic mode). Opus task keeps reading the TCP stream but discards frames. Mic audio is captured, mu-law encoded, and sent via UDP.
  • Button release: I2S switches back to speaker mode. Opus task resumes decoding and playing. The TCP connection stays alive throughout - no reconnection needed between turns.
  • Call end: Server closes the TCP connection. Device returns to idle, waiting for a new connection.

Hardware pin mapping (ATOM Echo)

Function GPIO Notes
I2S BCK 19 Shared speaker bit clock
I2S WS/PDM CLK 33 Speaker word select / mic PDM clock
I2S DOUT 22 Speaker data (NS4168)
I2S DIN / PDM DATA 23 Mic data (SPM1423)
Button 39 Active low, input only (no internal pullup)
LED 27 SK6812 RGB (1 LED, GRB order)

I2S quirks on ESP32-PICO-D4

The original ESP32's I2S driver with ALL_RIGHT channel format treats the DMA buffer as stereo-interleaved, unlike the ESP32-S3 which supports true mono. This means:

  • Speaker: sample_rate is set to SAMPLE_RATE / 2 (8000) so the effective mono playback rate is 16kHz
  • Mic: sample_rate is set to SAMPLE_RATE * 2 (32000) and samples are de-interleaved (every other sample) to get 16kHz mono
  • PDM mic channel: ALL_RIGHT is the only channel format that produces non-zero data from the SPM1423 on this board

Protocol compatibility

Uses the same TCP/UDP protocol as onjuino:

  • UDP 3000: Mic audio (mu-law encoded, 512 samples/packet)
  • TCP 3001: Server commands (0xAA audio, 0xBB LED set, 0xCC LED blink, 0xDD mic timeout)
  • Multicast: Device announces as "<hostname> <git-hash> PTT" on the configured multicast group

The PTT token in the multicast announcement tells the server to auto-start a call on discovery and keep the TCP connection open persistently (no silence-based disconnection).

Serial commands

Key Action
P Play local 440Hz test tone (bypasses network, tests I2S)
T Raw mic test (prints sample values)
M Force mic on for 10s (no button needed)
m Force mic off
A Re-send multicast announcement
c Enter config mode (ssid/pass/server/volume)
r Reboot

Config mode is also accessible during WiFi connection (if the stored SSID is wrong).

Building and flashing

From the repo root:

./flash.sh m5_echo              # auto-detect port, compile and flash
./flash.sh m5_echo compile      # compile only
./flash.sh m5_echo --regen      # regenerate WiFi credentials from keychain

Requires arduino-cli with the esp32:esp32 core. The flash script auto-installs required libraries (Adafruit NeoPixel, esp32_opus).

Testing

python serial_monitor.py     # serial monitor (auto-detects USB port)