STM32WB5MMG: data notifications degrade at 30–40 ft, and read/write requests then cause a multi-second stall or disconnect

[tmk]

Hi all,

I'd appreciate some help with a BLE range and stability issue.

 

Setup

• MCU: STM32WB5MMG module on a custom board
• Firmware package: STM32Cube FW_WB V1.23.0
• BLE wireless stack: v1.16.0, full stack
• TX power: +1 dBm
• Connection interval: 10 ms min / 15 ms max. Peripheral latency is 0 and the supervision timeout is 6 s.
• ATT MTU: 180
• Role: peripheral only. The central is a Windows 10/11 PC.
• PHY: Windows defaults to 2M PHY

Application

The peripheral sends data to the Windows central over GATT notifications at about 5400 bytes/s (~30 packets/s).

 

Problem

1. At short range, the data notifications work correctly.
2. As the distance grows to about 30–40 ft, data notifications start to struggle.
3. At that distance, if the Windows central reads or writes any characteristic, the device goes into an unknown state. For a few seconds it continuously sends unexpected data: the values 0x0839 and 0x08FD repeat every 64 bytes.

• Often the device recovers within a few seconds and then completes the read/write.
• Sometimes the stall lasts more than 30 seconds, and Windows then disconnects the device.

The behavior is repeatable.

 

Question

What could cause this? In particular:

1. Is there a known interaction between a GATT read/write request and heavy notification traffic when the link is weak and has many retransmissions?
2. Could this be buffer or flow-control exhaustion in the stack, and are there recommended settings for it?
3. Would you recommend any debug steps or stack configuration changes to narrow this down?

 

Thanks!