Hello,
my name is Rolf and I am new to this list. I think I may have found and issue
with libftdi (I am using the latest git at time of writing).
We have some hardware that has a FPGA connected to an FT245BL. We have been
using that on Windows with D2XX for some time (years). The data rate is quite
high, to operate the device we need to transfer around 500 KB/s (that means
KBytes).
The good news is that I could port our software to MacOS X 10.7 without too
much problems. I also can get the 500 KB/s data rate without errors, so the
application and the device is working.
BUT: Our FPGA has also a mode to test the maximum usb bulk transfer speed by
sending test data (incrementing 32 bit numbers) as quickly as possible. This
test fails with data losses on the libftdi/libusb-1.0/MacOS X stack. The test
reports around 450KB/s arrived in my application.
When I run the same test on the same machine/same device on a stack FTDI
D2XX/WinXP/VirtualBox/MacOS X I do not loose any data, but the data rate is
only about 530 KB/s. But at least the flow control is working here and we are
not loosing data with the D2XX driver.
When run on Windows on bare metal (no virtual box) the test typically gives us
something in the range of 1000KB/s to 1050 KB/s (without data losses).
The FPGA is designed to send data to the FT245BL whenever the FIFO can accept
data (as indicated by the handshake line). From my understanding there should
be no data loss. I do a ftdi_setflowctrl(p, SIO_RTS_CTS_HS) to enable
handshake, but that does not seem to help.
So my questions to the list would be:
- is a flow control problem with ftdi_read_data() known?
- how would I best debug this (since the issue only occurs at high data rate I
might not be able to printf-debug this)?
- Is virtual box also using libusb? If so, the problem would appear to be in
libftdi, otherwise it could also be an libusb issue.
When I get to work next week, I will also do tests on Linux. Maybe this is a
MacOS X only issue.
Any help is much appreciated,
Rolf
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