BLE OTA FIRMWARE Update Fails at 65% on STM32WB5MMGH6TR with Android

[MinhLuu]

I am experiencing an issue with OTA updates on the STM32WB5MMGH6TR when using an Android application. I would like your guidance and support in resolving it.

1. Device / Environment

• Device: STM32WB5MMGH6TR

• Android app: Custom OTA implementation using BluetoothGatt

• ST BLE Sensor Android App versions tested:

  • ST BLE Sensor 4.18.1 → OTA fails

  • ST BLE Sensor Classic 4.20.1 → OTA fails

  • ST BLE Sensor 5.2.10 → OTA works successfully

2. Problem Description

• OTA update fails consistently around 65% when updating to a different firmware version 

• Updating with the same firmware version works fine.

• Android BLE log shows:
   - system/stack/gatt/gatt_cl.cc:245 gatt_act_write: gatt_act_write() failed op_code=0x52 rt=143
   - system/bta/gatt/bta_gattc_act.cc:1132 bta_gattc_write: write status:0
   - system/btif/src/btif_gatt_client.cc:211 btif_gattc_upstreams_evt: Event BTA_GATTC_CONGEST_EVT [24]

• Using ST BLE Sensor 5.2.10, OTA completes successfully regardless of firmware version.

• Observed behavior:

  • Chunks sent via WRITE_TYPE_DEFAULT with size ≤ MTU-3

  • Notifications enabled on for ACKs

    0000FE23-8E22-4541-9D4C-21EDAE82ED19

    Android BLE stack fails mid-transfer on firmware, even with ACK-driven flow control

3. Steps Taken

1. Connect to normal mode (A7) → send OTA trigger → disconnect

2. Connect to OTA mode (A8)

3. Discover services, request MTU 251, enable notifications

4. Split firmware into chunks (max 200 bytes, WRITE_TYPE_DEFAULT)

5. Send next chunk only after STM32 OTA notification ACK

6. Retry mechanism implemented for failed writes

Observation: Despite proper ACK-driven chunk flow, OTA fails at ~65% when updating to a different firmware version, but works perfectly on THE SAME firmware.

Thansk,