Rx FIFO pointer behavior

[jgromes]

Hello everyone,

I would like to report an issue we are seeing in the behavior of the Rx FIFO pointer on LR1110 and LR1120 devices. In certain cases, the data received by the LR11x0 becomes corrupted by inadvertent shifts in the Rx buffer offset reported by the GetRxBufferStatus command.

In our usage, it seems that upon each packet reception, the reported offset always moves by 4 extra bytes when compared to the actual length of the received data. As an example, when a packet of 12 user bytes is received after a device reset, GetRxBufferStatus command returns length of 12, but an offset of 4. We compensate for this by calling GetRxBufferStatus command before reading any data. However, in certain cases, the RxBaseAddress pointer gets shifted by 8 bytes, while the offset reported by GetRxBufferStatus command only gets shifted by 4 bytes, which causes reading data from incorrect location in the Rx buffer, and so 4 additional bytes are prepended to the actual payload.

Therefore, I would like to ask the following:

1. Why is the reported offset always increasing by 4 bytes? The available documentation does not mention this behavior. The examples in the SDK repository shows that GetRxBufferStatus is being called, so this behavior would not manifest in the example.
2. Is there a mechanism that could cause the RxBaseAddress pointer to move by 8 bytes, while the offset in GetRxBufferStatus only moves by 4 bytes? We only notice the issue in congested RF environment, and it seems to happen when there are on-air collisions with other devices.
3. The user manual for LR1110 mentions in revision 2.2 (dated July 2025) in section 10.3 (page 108) that RxBaseAddr poitner can be set by the command SetBufferBaseAddresses. However, this command is not shown in the user manual, nor in this repository.

Thank you very much for any help you can provide. Please let me know if additional information is needed to investigate this.