>>>>> "Thomas" == Thomas Heller <theller@xxxxxxxxxx> writes:
Thomas> Sure it is something similar to /dev/null currently.
If there is some physical transfer I don't consider it as /dev/null...
Thomas> I'm using
Thomas> a FT2232H minimodule, TXE# is connected to WR#, and RXF# is
Thomas> connected to RD#. Let's just assume that my FPGA that I will
Thomas> connect next can keep up with the read/write cycles.
The FPGA should easily cope with the rate. What's hard to reach is the
timing. WR# needs minimum 11 ns before CLKOUT, so with 16.667 ns period you
have only 5.667 ns in the FPGA. You won't reach that with a XC6S-4 device. I
had to relax the constraints for about 1/2 ns.
Thomas> My program uses a home-grown ctypes based python wrapper for
Thomas> libftdi, it reads resp. writes in 1MB blocks from/to the
Thomas> minimodule. The functions that I use are ftdi_read_data() and
Thomas> ftdi_write_data(); the program measures the time that these
Thomas> calls take and reports a datarate of 19.xxx MB/s in each thread.
Thomas> I'm looking with an oscilloscope at the RD# and WR# signals, a
Thomas> screen shot is attached. I can see bursts of 8 block (of 512
Thomas> bytes probably).
With real data every time the FTx232H is not ready you need more clocks to
recover than with your data-shortcut. So data rate might drop. But we also
reach > 16 MByte/s.
Thomas> The PC is a lenovo W520 notebook, running Win7 64-bit.
A mighty machine...
Bye
--
Uwe Bonnes bon@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
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