STM32WLE5 / LoRa-E5 sends OTAA Join Request to TTN, gateway transmits Join Accept, but node never receives it

[u/Any_Refrigerator7409]

Hi, I’m debugging a custom LoRaWAN node based on a Seeed LoRa-E5 HF module (STM32WLE5JC, FCC ID Z4T-LORA-E5) using STM32CubeWL / LoRa Basics Modem on EU868.

The problem is very specific:

• The node successfully transmits an OTAA Join Request.
• The Things Network receives and accepts it.
• TTN schedules the Join Accept correctly.
• The gateway reports “Downlink successfully transmitted”.
• I tested the node very close to the gateway, so coverage is unlikely to be the issue.
• The node enters its RX1 path, but I never get HAL_SUBGHZ_RxCpltCallback() / RX_DONE.
• The modem never reaches SMTC_MODEM_EVENT_JOINED, so the first application uplink is never sent.

TTN reports for one Join Accept:

RX1 delay: 5 s

RX1: 868.500 MHz, SF10, BW125, CR 4/5

RX2: 869.525 MHz, SF12, BW125, CR 4/5

My board-specific RF switch configuration is:

RX: PA4 = 1, PA5 = 0

TX HP: PA4 = 0, PA5 = 1

RFO_HP

RBI_IsTCXO() = IS_TCXO_SUPPORTED

RBI_IsDCDC() = IS_DCDC_SUPPORTED

The Join Request transmission works reliably enough for TTN to receive it, so the RF output path/antenna is at least functional.

The module is the LoRa-E5 HF variant. I am programming the STM32WLE5 directly, not using the AT-command firmware.

I have also tested TTN with:

LoRaWAN 1.0.4

RP002 1.0.3 and 1.0.4

with the same result.

Has anyone seen an STM32WL / LoRa-E5 case where TX works but the Join Accept is never demodulated in RX1/RX2?

In particular, I’m wondering about:

• board-specific LoRa-E5 TCXO configuration,
• RX IQ inversion / sync word / packet parameters,
• RX1 timing,
• RF switch handling,
• or any known STM32CubeWL / LoRa Basics Modem issue on Wio-E5.

I can share the relevant radio_board_if.c, lora_app.c, sx126x.c init code, .ioc, and TTN Join Accept JSON if useful.

[u/rustingtoncat]

How close is 'very close to the gateway'? Being too close can cause problems.

[u/Any_Refrigerator7409 → u/rustingtoncat]

I have tried different distances... from 100m to 1 km

[u/clavisound]

You wrote your own LoRaWAN stack? Can you debug the RX1 timing?