Start of Transfer Detection is incorrect.

[emrainey]

start of transfer is indicated by a zero, not a 1.

out->start_of_transfer = (((frame->udp_cyphal_header.frame_index_eot) & (UDPARD_MAX_FRAME_INDEX)) == 1);

Should be

out->start_of_transfer = (((frame->udp_cyphal_header.frame_index_eot) & (UDPARD_MAX_FRAME_INDEX)) == 0);

[emrainey]

This was found during Service transfers but I would imagine it's happening all the time?

[lydia-at-amazon]

Hey Erik, thanks for pointing this out.

Looks like there a couple of things we need to change.

We are incorrectly setting the frame index to 1 instead of 0 when we call txMakeFrameHeader for both single frame transfers and multiframe transfers:

1. Single frame transfers: https://github.com/OpenCyphal-Garage/libudpard/blob/main/libudpard/udpard.c#L445
2. For multiframe transfers, we need to:
   • Increment the frame index after we call txMakeFrameHeader: https://github.com/OpenCyphal-Garage/libudpard/blob/main/libudpard/udpard.c#L560
   • Change this check from (frame->start_of_transfer && frame->frame_index != 1U) to (frame->start_of_transfer && frame->frame_index != 0U): https://github.com/OpenCyphal-Garage/libudpard/blob/main/libudpard/udpard.c#L994

I think there might be a few other places we need to update the logic as well.

[lydia-at-amazon]

Fixed by https://github.com/OpenCyphal-Garage/libudpard/pull/27