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.

	.text
	.org	0

#if THUMB_ENTRY
	.code	16
	bx	pc
	nop
#endif
	.code	32

/* delay loop like OsmocomBB does */
	mov	r1, #0xa0000
1:	subs	r1, r1, #1
	bne	1b
/* enable the Calypso boot ROM */
	ldr	r1, reg_addr
	mov	r2, #0x0100
	strh	r2, [r1]
/* jump to it! */
	mov	pc, #0
reg_addr:
	.word	0xFFFFFB10

#if PAD_TO_1003
	.org	0x3be0
	.ascii	"1003"
#endif