Control BaudRate USB port

This is a discussion on Control BaudRate USB port within the C Programming forums, part of the General Programming Boards category; I need to output a stream of binary data at a constant rate to a USB port. I am using ...

  1. #1
    carpe diem
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    Control BaudRate USB port

    I need to output a stream of binary data at a constant rate to a USB port. I am using Windows7, I can connect and send the data to the USB port but what I just can't control is the frequency at which the data is sent. Does anybody know any functions I can use so I can control the baud rate of data getting into a USB port?
    Do I need to use a Real Time OS?

  2. #2
    l'Anziano DavidP's Avatar
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    This seems like a really good article on the subject:

    Embedded.com - An Introduction to USB Development

    Sorry I'm not an expert at communicating through USB ports myself, but my guess is that it'd be hard to get a guaranteed data transfer rate if you're not on a real-time OS...simply because your subject to the scheduling of the operating system.

    Can you say what kind of app your working on? Is constant rate 100% necessary?

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  3. #3
    carpe diem
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    The stream of data needs to be recognized by a device that expects data in a specific format and specific frequency so constant rate is absolutely necessary - up to a 3% deviation is acceptable.
    Is there a way I can increase my driver/thread priority through my code so that the timing of the data won't be as suceptible to Windows scheduling?

    PS: Thanks for the article!

  4. #4
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    No idea about Windows but on *nix systems, it's sort of

    1. open() the USB device using its device file
    2. create a structure object of type struct termios
    3. call tcgetattr() to obtain the current port options
    4. set the input baud rate with a call to cfsetispeed()
    5. set the output baud rate with a call to cfsetospeed().

    Hopefully you can find something similar on Windows

  5. #5
    Captain Crash brewbuck's Avatar
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    USB has no "baud rate." If you need data to be transmitted at a particular rate, then... transmit it at that rate. I'm not sure what your question is.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  6. #6
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    The USB will have a baud rate if it is hooked to a serial port interface, which is what I thought the op had in mind when s/he posted the question. Guess the op will have to clarify what's exactly goin' on.

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