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MSP430 USB API stack interrupt duration / latency

dd ww
Prodigy 80 points

I am currently reading USB API documentation, but can not find details about interrupt behaviour. Can someone give me an approximate (cycles or time range) :

  • duration of USB ISR without event handlers in application space,
  • allowed latency of USB ISR because some other interrupt activity.

Put it in other words, what timing constraints does USB API put toward other interrupt sources?

 

  • 0
    Genius 3770 points

    As far as I know there's no precise timing constraints for your own ISR since each Usb packet is sent and received "asynchronously". The NAK bit is set until the MSP430 had time to finish processing and is ready for the next transaction. However the guide does mention a minimum of 1.5MHz for proper USB operation.

    Tony

  • 0 in reply to TonyKao
    Prodigy 80 points

    Thanks for your answer.

    We'll be using CDC class and Windows host, hope its driver (usbser?) will not complain about possible NAK's. I hope, this solves my second question.

    One of the time critical interrupt on our board will be some kind of soft uart on timer A with 1200 bauds, so max. duration of USB ISR can be ~1.5ms. I have no estimate on how time hungry the current USB API implemetation is, when executing interrupts. One can always rise MCLK, when executing soft uart, but I have to ensure worst case.

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