On Fri, Jun 17, 2011 at 1:23 PM, Caleb Kemere <ckemere@xxxxxxxxx> wrote:
> On Fri, Jun 17, 2011 at 1:07 PM, Uwe Bonnes
> <bon@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>>>>>>> "Caleb" == Caleb Kemere <ckemere@xxxxxxxxx> writes:
>>
>> Caleb> I've noticed previous threads where folks have used the
>> Caleb> synchronous FIFO mode of the FT2232H and gotten quite reasonable
>> Caleb> sustained transfer rates (15 MB/s). I'm struggling to get 6.5
>> Caleb> MB/s (without the buffer on the chip filling up). Is this an
>> Caleb> issue of the asynchronous FIFO mode, or am I somehow not pulling
>> Caleb> data off on the PC fast enough?
>>
Uwe> Otherwise, how do you read on the PC side? Do yo do asynchronous reads like
Uwe> in libftdi-1.0/src/ftdi_stream.c?
I did test the asynchronous mode, but now I think I've distilled the
essence of the test down to the following really simple (blocking)
code:
int transferred = 0;
int bytes = 0;
while (bytes < MAXIMUM_TRANSFER) {
last_result = libusb_bulk_transfer(ftdi.usb_dev, ftdi.out_ep,
buffer, bufferSize, &transferred, 1000);
if ((last_result > 0) | (transferred == 2))
break;
else
bytes+= transferred;
}
I've been messing around with different values for the read-chunksize
of the FT2232H and the bufferSize of the bulk transfer. As a reminder,
my data streams from the FPGA to the FT2232H at 6.5 MB/s. With that, I
can consistently read for about a 30 s or so before I get a buffer
overflow (at half speed, I can go for about 3 times that long). It
seems like the USB subsystem should be able to handle that data rate
for an arbitrary length of time, so I'm wondering what I could be
doing wrong...
thanks!
– caleb
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