Thank you Uwe. The FTDI device I am using is FT245BM and not x232H. I
will look into the document you sent me and see how things go from
there.
Thanks,
KM
On 23 September 2011 09:54, Uwe Bonnes
<bon@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> >>>>> "KrishnaMohan" == KrishnaMohan Bandi <krishnamohan.bandi@xxxxxxxxx>
> >>>>> writes:
>
> KrishnaMohan> --20cf3040e9c665eee404ad850ce7 Content-Type: text/plain;
> KrishnaMohan> charset=ISO-8859-1
>
> KrishnaMohan> Hi all,
>
> KrishnaMohan> I have a program that uses libftdi-0.19 library to read
> KrishnaMohan> and write from/to a FTDI device, which on the other end is
> KrishnaMohan> connected to an FPGA. I do not have more than 20 bytes of
> KrishnaMohan> data at any time to send/receive to/from the FTDI device,
> KrishnaMohan> however I do very frequent reads and writes (approximately
> KrishnaMohan> every 15ms) from/to the FTDI device to read the GPS clock
> KrishnaMohan> time and some other registers from the FPGA.
>
> KrishnaMohan> The read and write are together taking about 5-8ms and
> KrishnaMohan> sometimes it goes up to as high as 15ms. This means the
> KrishnaMohan> transfer rate is not even 9600bits/sec. However, the baud
> KrishnaMohan> rate has been set to 921600. On the FPGA side, the time to
> KrishnaMohan> read, process, and write back the data to the FTDI does
> KrishnaMohan> not take more than 100uS. So, for the program the data is
> KrishnaMohan> available as soon as the data is written to the FTDI
> KrishnaMohan> device.
>
> KrishnaMohan> The strange behaviour I noticed is that when
> KrishnaMohan> ftdi_read_data() is called, it returns zero as the number
> KrishnaMohan> of bytes read.
>
> Are you sure the data has already been delivered to the FTDI chip? Have a
> deep look at
> http://www.ftdichip.com/Support/Documents/AppNotes/AN232B-04_DataLatencyFlow.pdf
> to understand the issues involved.
>
> Chapter 3.1, point 2 might help: Toggle some status line when the device has
> send the data to the FTDI chip.
>
> KrishnaMohan> Only, the third (always) time the
> KrishnaMohan> ftdi_read_data() actually reads the data and about 3ms is
> KrishnaMohan> elapsed between the time the data is available and the
> KrishnaMohan> ftdi_read_data() is actually able to read the data from
> KrishnaMohan> the FIFO.
>
>
> KrishnaMohan> What I want to know from you guys is why is
> KrishnaMohan> ftdi_read_data() takes so much time to read small amount
> KrishnaMohan> of data? What should be done to reduce the read/write time
> KrishnaMohan> to the FTDI?
>
> Is this with a x232H chip or an old type USB full speed chip. In the
> latter case, add a USB2.0 High-Speed Hub in between.
>
> ...
>
> KrishnaMohan> Hi all,<br><br>=A0=A0 I have a program that uses
>
> Please, no HTML in Mail.
> --
> Uwe Bonnes bon@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
> --------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
>
> --
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