Hi all, This email is related to the "Minimum Chunk Size and Latency" thread by Daryl Lee about a month back. I am using an FT232R chip in an application which requires low latency but doesn't really care much about the load on the line (very quick packets of varying small sizes). I am in linux and want to use the VCP driver with termios to configure the UART - the program is already written in such a way.
Without configuring the chip at all I see a ~16 ms delay on a read command (I assume this is related to the timeout), which is out of spec for my application. When I go to lower the chunk size and latency using libftdi, I can set it and read it back, but then when I try to switch back to VCP mode I get a /dev/ttyUSB0 not found error. I assume that libftdi disables the VCP driver or something? I then cycled the power on the chip and was able to access ttyUSB0 again, but the configuration reverted to the defaults. And I am guessing that the configuration information is not stored on the EEPROM. So my question boils down to this (assuming that I haven't totally misread the documentation)... 1) How would I configure the chip and then proceed to use VCP? 2) After I am able to change the latency and chunk size, can I simply drop them down very low or, as Daryl saw, is there an optimal value for varying sized packets. (I suppose I can figure this out empirically) Thank you, -Ben -- Ben Plotnick University of Pennsylvania [email protected] -- libftdi - see http://www.intra2net.com/en/developer/libftdi for details. To unsubscribe send a mail to [email protected]
