Ok, I think I understand more about what is going on. In the
ftdi_read_data() function:
if (ret > 2) {
// skip FTDI status bytes.
// Maybe stored in the future to enable modem use
num_of_chunks = ret / 64;
chunk_remains = ret % 64;
//printf("ret = %X, num_of_chunks = %X, chunk_remains = %X,
readbuffer_offset = %X\n", ret, num_of_chunks, chunk_remains,
ftdi->readbuffer_offset);
ftdi->readbuffer_offset += 2;
ret -= 2;
if (ret > 62) {
for (i = 1; i < num_of_chunks; i++)
memmove (ftdi->readbuffer+ftdi->readbuffer_offset+62*i,
ftdi->readbuffer+ftdi->readbuffer_offset+64*i,
62);
if (chunk_remains > 2) {
memmove (ftdi->readbuffer+ftdi->readbuffer_offset+62*i,
ftdi->readbuffer+ftdi->readbuffer_offset+64*i,
chunk_remains-2);
ret -= 2*num_of_chunks;
} else
ret -= 2*(num_of_chunks-1)+chunk_remains;
}
} else if (ret <= 2) {
// no more data to read?
return offset;
}
The code assumes that there will be a modem status byte pair for every 64
bytes returned by the ftdi chip. For the ft245BL, this is true. For the
ft2232H, it appears that the modem status bytes are returned only once per
usb_bulk_read call. Setting a break at "if (ret > 2)", I examine the results
of the bulk_read. There are 106 bytes total. The first two bytes are the
modem status bytes as expected. The remaining 104 bytes are the data sent
from my device, with no additional modem status bytes embedded in the
stream. Thus, as the code stands now, it will delete bytes 65 and 66,
thinking that they are modem status bytes, when in fact they are not.
Could this be the issue? Is there anything else I can do on my end to prove
this out? What would be the suggested fix?
Thanks,
Dave Challis
--
libftdi - see http://www.intra2net.com/en/developer/libftdi for details.
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