int ok = 0;
int len = 0;
int block_size = 256;
while (!ok) {
    written = ftdiread(buf+len, block_size); // get byte
    len += block_size;
    printf("%6d%c%c%c%c%c%c%c",len,8,8,8,8,8,8,8);
    written = ftdiread(bufstart, 1); // status
    ok = bufstart[0];
}
printf("\n");