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.

/*
 * This header file is a FreeCalypso addition.  It serves a purpose similar to
 * fixedconf.h and condat-features.h in gsm-fw/include, but this one is local
 * to the ACI component.
 */

#define	DTI	1

#if CONFIG_UI
#define	MMI	2
#define	MFW	1
#else
#define	MMI	0
#define	ACI	1
#endif