Unclear code fragment in rfm_filop_write()

[nxdefiant]

In rfm_filop_write() you are using this code fragment to increment the out_cur_end pointer to the end of the current buffer:

*rfm12->out_cur_end++ = 0;         // hdr
*rfm12->out_cur_end++ = (u8)copied;   // len
rfm_apply_crc16(rfm12, rfm12->out_cur_end-2, copied+offset);
rfm12->out_cur_end += copied + offset;

which is a bit confusing for me. If I understand this correctly the pointer increment in the first 2 lines actually does increment the pointer for the crc at this place, not the header (which is also 2 bytes), because the length of the header is already accumulated in offset.

recommended rewrite:

*rfm12->out_cur_end = 0;
*(rfm12->out_cur_end+1) = (u8)copied
rfm_apply_crc16(rfm12, rfm12->out_cur_end, copied+offset);
rfm12->out_cur_end += copied + offset + 2; // +2 byte crc

I stumbled about this when attempting to use your code with a protocol that does not know the first header byte, after a few modifications it works, thanks for sharing the code.

Also please use constants for header and crc length instead of using the value 2 for both. Sometimes it is a bit hard to spot which is which.