Code in tightly coupled memory

This works:

int testcall(int n)   __attribute__ ((section (".tc_code")));
int testcall(int n)
{
    int i;
    i = n;
    while (i > 0) {
        n += i--;
        IOWR_ALTERA_AVALON_PIO_DATA(IO24V_PIO_BASE, n);
        printf(".");
        }
    IOWR_ALTERA_AVALON_PIO_DATA(IO24V_PIO_BASE, 0x55);
    return n;
}

I inserted the IOWR and printf to increase code size and have a call to a function in sdram, like the 'real' case.

This DOES NOT work:

int pkt_send(char *data, int len) __attribute__ ((section (".tc_code")));
struct buffer_t 
{
    int len;
    unsigned char data;
} buffer_tx;
int pkt_send(char *data, int len) 
{
    short index;
    // is next buffer valid?
    index = pkt_send_count & 0x07;
    if (buffer_tx.len != 0) 
        return 0;
    if (len >= 0x600)
        len = 0x600;
    memcpy(buffer_tx.data, data, len);        
    buffer_tx.len = len;  
    ++pkt_send_count;
    return len;
}

Remarks:

- buffer_tx resides in sdram

- pkt_send() works perfectly when I remove the attribute directive

- testcall() is called in the very beginning of program; pkt_send after uC RTOS tasks have been initialized

Thank you for any help

Cris