MeshCore/variants/lierda_am36_pico

MeshCore on the Lierda AM36 Pico (L-LRMAM36-FANN4-PK02)

Community variant for the Lierda AM36 Pico evaluation board. The on-board L-LRMAM36-FANN4 module is an ESP32-S3 (8MB flash / 8MB PSRAM) paired with a Semtech LR2021 Generation-4 LoRa transceiver.

Status: hardware-validated (Jul 2026) on a live mesh: radio init, noise floor sampling (~-119 dBm), BLE pairing with the iOS companion app, flood + direct TX with interrupt-driven send-complete, and two-way messaging with a Heltec Tracker v2 (SX1262) peer - i.e. confirmed LR2021 <-> SX1262 interop - at 927.875 MHz / BW 62.5 / SF9 / CR7, both nodes using muzi works 17 cm whip antennas (replies at SNR 3.25 dB). Also received channel messages from six third-party senders at 3-9 hops with full path reconstruction, and measured a third-party repeater (not operated by the author) at up 11.5 dB / down 13.0 dB. Requires the CustomLR2021 radio classes from MeshCore PR #2944.

Hardware facts used by this variant

Signal	ESP32-S3 GPIO	Source	Verified
LR2021 SPI SCK	40	esp32_lora_driver Kconfig (LIERDA_BOARD_LRMAM36_FANN4)	yes (on air)
LR2021 SPI MOSI	41	same	yes
LR2021 SPI MISO	42	same	yes
LR2021 NSS	39	same	yes
LR2021 NRST	38	same	yes
LR2021 BUSY	17	same	yes
LR2021 IRQ	21 - wired to LR2021 DIO7	Kconfig LR20XX_DIO7_GPIO	yes (TX-done + RX interrupts)
KEY button	4 (schematic net GPIO4/KEY1)	schematic	not yet - left disabled

The IRQ DIO matters: the Seeed Wio-LR2021 (which PR #2944 targets) uses DIO8, so this variant sets -D LR2021_IRQ_DIO=7. No external TCXO or RF-switch GPIOs exist on the MCU side - the module handles RF internally. The board's only LED is a hardwired 3V3 power indicator, so no PIN_STATUS_LED is defined.

Build

1. Install VS Code + the PlatformIO extension.
2. Get the source with the LR2021 driver:

   git clone https://github.com/meshcore-dev/MeshCore
   cd MeshCore
   git fetch origin pull/2944/head:lr2021
   git checkout lr2021
   

   (Once PR #2944 is merged, plain dev works.)

3. Copy this lierda_am36_pico/ folder into variants/. (PlatformIO auto-discovers variants/*/platformio.ini.)
4. Radio parameters: builds inherit MeshCore's defaults; set your region's frequency/BW/SF/CR from the companion app after first boot (settings are persisted on the device), or override LORA_* flags in a platformio.local.ini for your own builds. The module covers 863-930 MHz.
5. Build:

   pio run -e Lierda_AM36_Pico_companion_radio_ble
   

   Other envs: ..._companion_radio_usb, ..._repeater. Note: the iOS companion app connects over BLE only, so iPhone users want the _ble build.

Flash

1. Connect the Type-C port labelled USB (NOT the one labelled UART - that goes to the CP2105 bridge). The USB port is the ESP32-S3's native USB-JTAG/CDC and is what esptool talks to.

2. pio run -e Lierda_AM36_Pico_companion_radio_ble -t upload
   

3. If the port doesn't enumerate or upload fails to sync: hold BOOT, tap RST, release BOOT (forces download mode), then retry the upload.
4. Tap RST after flashing completes.

Verify

• Serial console is on the same USB port (pio device monitor -e Lierda_AM36_Pico_companion_radio_ble). Note the ESP32-S3 re-enumerates USB on reset, so the monitor may need a restart after tapping RST. A failed radio bring-up prints ERROR: LR2021 init failed: <code> and halts (no BLE advertising).
• Attach the LoRa antenna before any TX.
• Pair from the MeshCore app over Bluetooth (default PIN 123456, set via BLE_PIN_CODE), set your region's radio parameters in the app, and send a channel message or advert.

Known quirks / notes

• SPI to the LR2021 sits on GPIO39-42, which are the S3's JTAG pins. That's fine (flashing/debug uses USB-JTAG), just don't try external JTAG.
• PSRAM is present but left disabled - MeshCore doesn't need it, and octal PSRAM misconfiguration is a classic S3 boot-loop source.
• The KEY button (schematic net GPIO4/KEY1) is left disabled until traced on hardware; uncomment PIN_USER_BTN in platformio.ini once confirmed.
• PR #2944's wrapper drops the radio to standby before every startReceive() (LR2021 wedges if re-armed mid-RX) - don't "optimize" that away.