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MSP432P401R: msp432 dma peripheral trigger, edge or level? please clarify

Eric Decker
Expert 1420 points

Part Number: MSP432P401R

According to the latest msp432 Technical Reference Manual (slau356E, Dec 2016) on page 468, section 9.2.5

however, I've been working with the example dma code (using the rom based driverlib), version 3.50.0.2, dma/dma_eusci_spi_loopback/dma_eusci_spi_loopback.c.

this program starts out with TXBUF being empty which means TXIFG is up (this is on the master SPI, B0).  Nothing special is done with TXIFG.  Rather, DMA channel 0 is simply enabled and off to the races we go...

That's a level, no edge involved.

Can you please talk to the design folks and let me know if I'm not understanding something properly.

thanks,

eric

  • 0
    TI__Guru 55136 points
    Thanks Eric. I will ask for some clarification. Given the holiday it may take additional time. This note was added relatively recently to address a concern/confusion relating to the DMA trigger from the IO. I believe that there is logic between the peripheral trigger and the actual DMA trigger, so in a sense it sees and edge when enabled. To be sure that is just a guess on my part and will work with the team to provide a more clear explanation.

    In the context of the example you site, if the DMA wrote to some other location other than the TX buffer and consequently the IFG (trigger) was not cleared would you expect the DMA to continue because the level remains constant?

    Regards,
    Chris
  • 0 in reply to Chris Sterzik
    TI__Guru 55136 points
    Eric,
    I was able to confirm with design that it is edge triggered and that the 'edge' is created when the mux selects the signal that is already at a high level.

    Regards,
    Chris
  • 0 in reply to Chris Sterzik
    Expert 1420 points

    Chris Sterzik said:
    Eric,
    I was able to confirm with design that it is edge triggered and that the 'edge' is created when the mux selects the signal that is already at a high level.

    Regards,
    Chris

    Very nice.  thank you so much for tracking this down.

    I would click "VERIFY ANSWER" but I don't see one (the button that is) :-)

    [Oh there it is.  Done]

  • 0 in reply to Eric Decker
    Expert 1420 points
    Also can you have the documentation enhanced so that it discusses this a bit.

    the way it is currently written implies that one has to play games to get the DMA to take off and that isn't the case.

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