Modem crash with 0x4 while using DECT nr+ MAC/DLC APIs

[0x41]

Hi everyone,

I'm developing a star-topology network using DECT NR+ on nRF9161 DK nodes,
running modem firmware mfw-nr+_nrf91x1_2.0.0 (nRF Connect SDK 3.3.0).

My issue is a modem crash with error 0x4 on the FT side when it receives
a PDU of ~3200 bytes sent by the PT device via
nrf_modem_dect_dlc_data_tx(). After investigating the error code, I
increased the modem's shared memory using
CONFIG_NRF_MODEM_LIB_SHMEM_RX_SIZE, but the crash still occurs at this
payload size.

On the PT device side, the transmission itself doesn't seem to fail,
since the dlc_data_tx callback is called with status 0.

For clarification: the FT and PT nodes start exchanging data after
association. I haven't yet tried to reproduce the crash using the sample
application from [Hands on with DECT NR+ API release v2.0], and I also
wasn't able to capture a modem trace of the fault using the Modem
library.

Modem error: 0x4
PC: 0x561bc
SDK: 3.3.0

Sorry in advance if I've left out any details.

Kind regards,
Alessandro.

[Syed Maysum Abbas Zaidi]

Hi,

Thanks for waiting. We can see that the modem crashes when it runs out of large internal memory blocks while processing the received large SDU.

On our side, data up to 4KB went through successfully using the NCS DECT NR+ stack. We understand you need DLC segmentation directly, but is it possible for you to try NCS DECT NR+ socket-based stack to confirm the issue doesn't occur there? It uses the same DLC layer internally. 

Best Regards,
Syed Maysum