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CJvanSoest edited this page May 25, 2026 · 2 revisions

C6 radio communication

The Tanmatsu has two ESP32 SoCs: the ESP32-P4 runs the app + display, and the ESP32-C6 drives the SX1268 LoRa transceiver. The P4 talks to the C6 over a hosted-WiFi-like SDIO/SPI link via Nicolai Electronics' tanmatsu-lora IDF component (which exposes lora.h).

RPC surface (lora.h)

Function Purpose
lora_init(qsize) Bring up the RPC link, allocate RX queue
lora_get_config(&cfg) Read C6-side config (frequency, SF, BW, CR, power, sync, preamble)
lora_set_config(&cfg) Push P4 config to C6 — applied immediately
lora_set_mode(MODE) RX, TX, SLEEP
lora_send_packet(buf, len) Enqueue a TX
lora_recv_packet(...) Pop the next received frame

radio.c builds an RX task that loops on lora_recv_packet. RSSI/SNR fields are populated only when the firmware on the C6 supports them — see below.

RSSI / SNR patches

The stock tanmatsu-radio v2.12.3 does not surface per-packet RSSI / SNR to the host. We run a patched build that:

  1. Reads RSSI/SNR registers after each SX1268 RX_DONE IRQ
  2. Stores them in the per-packet metadata
  3. Returns them via the existing lora_recv_packet struct

The patch lives in a local checkout (not an upstream PR) and must be re-applied after upstream releases.

In the Nodes tab the RSSI column is coloured:

RSSI Colour
≥ -80 dBm Green
-80 .. -105 dBm Amber
< -105 dBm Red

SNR (in dB):

SNR Colour
≥ 0 dB Green
-10 .. 0 dB Amber
< -10 dB Red

Frequency / band

Default is the EU 868 ISM band:
Default frequency 869.618 MHz (MeshCore canonical)
Band EU 868 (863–870 MHz allowed)
Channel BW typically 62 kHz, configurable 7–500 kHz
TX power up to 22 dBm (chip max; legal cap is lower in EU)

US, JP, AU and other bands work too — set frequency to the matching ISM band frequency. The chip itself is multi-band; the Tanmatsu RF front-end is optimised for 868/915 MHz.

Firmware update workflow

The Settings tab U key triggers enter_radio_bootloader() which:

  1. Stops the ESP-Hosted heartbeat
  2. Deinits ESP-Hosted
  3. Powers the C6 OFF, then back ON in BOOTLOADER mode
  4. Replaces the screen with the esptool command sheet

Then on the Mac:

esptool.py --chip esp32c6 --port /dev/cu.usbmodemXXXXX --before no_reset \
  write_flash --flash_mode dio --flash_freq 80m --flash_size 8MB \
  0x0     build/tanmatsu/bootloader/bootloader.bin \
  0x8000  build/tanmatsu/partition_table/partition-table.bin \
  0xd000  build/tanmatsu/ota_data_initial.bin \
  0x10000 build/tanmatsu/tanmatsu-radio.bin

--before no_reset is critical — the C6 is already in DFU, we don't want esptool to toggle the reset line. After flashing, press ESC / F1 to power cycle the badge. On the next boot MeshCore detects the blank C6 NVS (frequency = 0) and re-pushes the saved LoRa config.

Mismatch warning in launcher

The Tanmatsu launcher checks the C6 firmware version against its embedded expected version. We ship tanmatsu-radio v2.12.3 (+RSSI/SNR patches) which is newer than the launcher's expected v2.7.3, so it prints a "mismatch firmware" warning. Ignore it — the MeshCore app talks to the radio directly and works fine. Do not click "Update Radio" in the launcher; that downgrades the C6.

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