AT command interface works! The cause of the breakage was the same Nucleus API issue with NU_Create_Timer() which we encountered at the very beginning of this project with Riviera timers: the code in uartfax.c from TCS211 was passing 0 as the initial dummy value for the timer duration, and our FreeNucleus version doesn't like it. The fix is the same: pass 1 as the initial dummy value instead.

/*
 * If you need to build a version of loadtools without compalstage support,
 * e.g., because you are building for GTA01/02 AP, substitute this dummy
 * module in the place of compalload.c to get a passing build.
 */

void
set_compalstage_short()
{
}

void
set_compalstage_fullpath()
{
}

perform_compal_stage()
{
	return(0);
}