3 Replies Latest reply on Jan 4, 2012 6:01 PM by user_78878863

    DMA termout/nrq and bursts

    douglas.mcclean

      I have a question about the PSoC5 DMA, and I'm not confident of my interpretation of the app note on this point.

         

      If I set the DMA__TD_TERMOUT_EN flag on a transaction descriptor, do I end up getting one pulse on nrq at the end of the entire TD? Or one at the end of each burst that that TD does?

         

      Specifically, I'd like to set up the DMA to transfer 1kB from a UART to SRAM. I plan to set it up so that the TD does 1 byte per burst, and requires a request per burst. I plan to tie the rx_interrupt line from the UART (with the On Byte Received interrupt enabled) to the drq line on the DMA.

         

      I'd like to get one interrupt when the entire 1kB is transfered, so that I can process that block and set up for receiving the next one, what I don't want is one interrupt after each byte.

        • 1. Re: DMA termout/nrq and bursts
          user_78878863

          The datasheet states "The DMA generates a pulse of width two bus clocks at the
          nrq when the DMA transfer is complete." This means the end of the whole TD.

             

          I suggest you read the app note about the DMA (see http://www.cypress.com/?app=forum&id=2492&rID=53352 ) and the one about interrupts (see http://www.cypress.com/?app=forum&id=2233&rID=57231 ). Especially the latter one will be important for you, because the UART component doesn't create an interrupt per byte received, but stays high as long as a byte is in the receive buffer. You will need to take that into account.

          • 2. Re: DMA termout/nrq and bursts
            douglas.mcclean

            Thanks!

               

            I had seen that sentence but didn't know how to interpret it. If someone reads this who is in charge of the app note, adding a phrase to explain that might be helpful to the next person.

               

            I hadn't realized the UART byte received interrupt would stay high. This shouldn't be a problem if I set the DMA component's "Hardware Request" property to "Level", though, if I understand correctly. Thanks for the heads up.

            • 3. Re: DMA termout/nrq and bursts
              user_78878863

              The proper explanation is hidden in the description of the TD_TERMOUT_EN flag - there it says 'when this TD completes'. If I think about it, this would mean if you have multiple TDs chained together, each one would (potentially) generate a trigger signal. I think it might be a good idea to add this explanation to the output signal (nrq) documentation.

                 

               

                 

              I was not aware that the DMA could be trigger by a level signal - but it is actually what you need. Sounds like a good plan, then. Can you keep us informed when you got it working?