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USB2 Loopbacks and duty cycle setting

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  • Ian (PassMark)
    By design, the duty cycle setting is not linear with the USB 2.0 testing. This was changed in V5 on request of a number of customers, that had USB problems and wanted to be able to introduce much greater delays to help their investigations. In your case, it sound like you just want a Duty cycle setting of 50 or more.

    To be more precise, the following is a description of the duty cycle delays inserted in V5.0 and V5.1:

    Duty cycle delay 100:
    No introduced delays.

    Duty cycle delay 1 99:
    Between every 8000 writes/reads, a delay of at least x ms is inserted.
    Where x = (100-dutyCycle)*70

    Duty cycle delay 1 49:
    Additionally, between each write/read cycle at least x ms delay inserted.
    Where x = (50-dutyCycle)/2

    Duty cycle 0 - 9:
    Additionally, at least 1 ms delay inserted between write and read.

    We will update the help file.

    FYI, we did change the RAM duty cycle settings in V5.x to make it more linear.

    Leave a comment:

  • DanB
    started a topic USB2 Loopbacks and duty cycle setting

    USB2 Loopbacks and duty cycle setting

    Need to exercise all systems ports (serial, parallel, network, USB, RAM, hard drives, etc) simultaneously for EMI testing. Ideally we'd like to complete a single pass as fast as possible (running in continuous mode).

    Had problems with version 4.0 related to serial port errors. Decided to upgrade to version 5.1.

    Seeing a problem in version 5.1 related to USB Loopbacks and duty cycles. Testing (5) USB 2.0 Loopbacks.

    With USB duty cycle set at or below 48, 7 cycles passed in 4+ hours.
    With USB duty cycle set at or above 49, 20 cycles passed in 5 minutes.

    Note that in version 4.0 the USB duty cycle setting appeared to work "properly". We also saw similar problems in version 4.0 for the RAM duty cycle setting- duty cycle 99 and the test crawled; duty cycle 100 and the test ran fast. Note that the RAM duty cycle setting appears to have been corrected in version 5.1.