I was able to get an ATMEL Start based USB CDC ACM Echo example up and running. After initializing the stack, I install a STATE callback and in the state callback I install read and write callbacks. After setting up a first read, I can write what has been read and setup a new read.
But: If I try to write a welcome message in the state callback using cdcdf_acm_write(), neither the message is send out (or at least, I don't see it in my terminal emulation), nor does the cdcf_acm_write() function return an error. If I dispatch the state callback to my main loop and call cdcf_acm_write() from there, I "see" the same effect (no message, no error). If I issue a delay before sending out the message, the message is received by the terminal. Debugging the problem is hard, as stepping through cdcf_acm_write() already introduces a delay.
Is there something obvious, I could do wrong (misconfiguration etc.)? Is this a known bug? Is there something else I could wait on, before start sending data? ( assert( cdcdf_acm_is_enabled() ) doesn't fail)
According to AtmelStart.env_config, I'm using version 1.2.139 configured for a ATSAMD51J19A.
Thanks in advance,