Prototype dual-radio channels on RadioMaster Nomad

[h3lix1]

Summary

This draft prototypes both LR1121s in the RadioMaster Nomad as independent Meshtastic PHYs:

• the primary radio follows config.lora and was tested as US MediumFast at 913.125 MHz
• logical channel 1 uses the second LR1121 with a fixed US ShortTurbo profile at 926.750 MHz
• both paths may transmit, with a nominal 10 dBm hard cap and one-at-a-time TX coordination
• the peer radio enters standby before TX, APC2 is serialized, and both paths return to receive afterward
• two-slot RadioLib ISR dispatch and an alternate LoRa transport tag support the two radio instances
• GPIO2 fan control remains available through lora.pa_fan_disabled

This is an experimental continuation of the Nomad bring-up in #5318 and the hardening delta in #11141.

Why

Meshtastic currently exposes one router-facing radio interface, while logical channels are cryptographic namespaces rather than per-channel PHY configurations. This composite interface is a small test vehicle for assigning one logical channel to each physical LR1121 before attempting a true cross-channel bridge.

Current limitations

• This does not bridge channel 0 traffic into channel 1. A bridge would need an explicit decrypt, clone, re-encrypt, and loop-control policy.
• Secondary selection uses Meshtastic's 8-bit encrypted channel hash, so a collision is possible.
• PKI direct messages still use channel zero.
• The external PA table and antenna-port isolation are not calibrated.
• No external ShortTurbo peer acknowledged the channel-1 test packet.
• Simultaneous TX and high-power testing are intentionally excluded.

Validation

• trunk fmt
• git diff --check
• Clean pio run -e radiomaster_nomad_gemini from commit defe8b60f7973ee94950ebe893d88bb0ed3e06c2
• Factory image flashed to the ESP32-PICO-D4 with esptool hash verification
• Exact artifact booted as 2.8.0.defe8b6
• Both LR1121s initialized: MediumFast 913.125 MHz and ShortTurbo 926.750 MHz
• Live MediumFast packets received with RSSI/SNR data; node database reached 120 entries
• Primary traceroute completed:
  • outbound: !5868023a -> 0b45f21f -> a0352604 -> !4703f8ab
  • return: !4703f8ab -> 273c3874 -> !5868023a
• Channel-1 packet 0x78bac82c was selected for ShortTurbo and reported TX-done on each retry
• Wi-Fi rejoined the configured network, obtained 192.168.1.252, answered ICMP, and served the TCP API on port 4403
• Fan disable and enable settings both wrote and read back; final state commands the fan on

The repository test wrapper is blocked on macOS by Bash mapfile and BSD find lacking -printf. Direct native tests are independently blocked by existing macOS-incompatible VLAs and linux/input.h; neither failure reaches the Nomad-specific code.

Review focus

• composite ownership and Router-facing behavior
• dual-instance ISR dispatch
• SPI, standby, APC2, and TX-arbiter sequencing
• logical-channel selection and relay-path preservation
• whether the prototype constraints are sufficient before any calibrated RF work

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[thebentern]

Super neat!

[h3lix1]

Closing this one out - Does not seem to have much traction