In the example codes posted under trx_examples/targeting/modem-qpsk/test/linux of the TransceiverToolbox repository in github, I noticed a couple differences between test_dma.c and modemd.c.
1. In modemd.c, in line 220, the TX transfer size for the radio IP is written at the top of the DMA buffer. However, instead of the number of bytes to be transferred, a bit-reversed copy of that uint8 number is written.
2. In test_dma.c, in line 108, the TX transfer size is written directly without any bit reversal.
Why does the difference exist? Also, in modemd.c the number being written is an uint8 which will overflow with larger MTU sizes. How is that dealt with?