Adam Dunkels writes on 2/5/2017 on the Contiki mailing list:
[...] the original idea was that the application could just point the uip_appdata pointer to wherever the data was, but we then changed it so that the data actually had to be copied into the uip_aligned_buf buffer. So, yes, the network device driver should only need to read from this buffer. [...]
This change removes comments on the possibility of uip_appdata pointing somewhere outside the uip_aligned_buf. And it removes code in the SLIP drivers not necessary anymore.
Additionally it makes code in a SLIP driver optional that takes care of the Microsoft-specific CLIENT / SERVER / CLIENTSERVER chat.
