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.

/*
 * Definitions of global variables for the tiffs IVA program.
 */

#include <sys/types.h>
#include "types.h"
#include "struct.h"

char *imgfile;
off_t imgfile_offset;
u32 eraseblk_size;
int total_blocks;
u32 total_ffs_size;
int index_blk_num = -1, root_inode;
int inode_limit;
int verbose, verbose2;

u8 *image, *inode_block;
struct inode_info **inode_info;