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USB virtual COM port latency RRS feed

  • Question

  • Hi

    I have ran into an issue and a friend working for MS redirected me here. I hope I am posting this in the right place, because I am new here. Anyways to the issue:

    I am using an FTDI chip to connect a processor UART channel to the computer via a virtual COM port. The chip can achieve the speed of 3MBd. I have been expecting to use this speed, but ran into a problem on the computer side. Settings in the device manager allows lowest latency of 1ms. Given that most of my data are only small data packets, this latency is really slowing me down. Workaround from FTDI is not to use the virtual com port driver, but D2xx instead, but that would mean writting own program on the PC side as well as breaking up my existing software. I wanted to ask, if there is a way to lower this latency further down? Ideally to about 0.1ms.

    Thanks in advance for any answers

    Saturday, August 8, 2015 10:36 AM

All replies

  • I forgot to mention that FTDI claims, that the data from the COM port is handled by an USB HID layer before being passed to the FTDI driver. Thats why I am posting here and not there. Sorry for my error...
    Saturday, August 8, 2015 10:38 AM
  • Pavel, have you made any progress with this issue?
    Thanks!

    Ed Price, Azure Development Customer Program Manager (Blog, Small Basic, Wiki Ninjas, Wiki)

    Answer an interesting question? Create a wiki article about it!

    Tuesday, December 20, 2016 6:44 AM
  • Sorry for the delay, didnt notice your reply. No, the issue was never solved.
    Wednesday, November 1, 2017 2:26 PM
  • This latency is limitation of the FTDI emulated serial driver, not of Windows (yes, the TFDI driver has a custom property page in Device Manager). 

    FTDI claims, that the data from the COM port is handled by an USB HID layer before being passed to the FTDI driver.

    It was a very strange claim. Maybe, mistake in translation. Even if true, it would be an internal detail of  FTDI driver.

    Another Pavel

    -- ap

    Wednesday, November 1, 2017 5:34 PM