1 Reply Latest reply on Oct 31, 2015 10:27 AM by JeCo_264681

    Accessing variable starting points in an array with DMA


      Hello my PSoC heros!


      Theoretical setup:


      A series of 11 arrays with 4000 bytes each filled by  DMA_1 with chained TDs as a circular buffer of 8bit audio samples from an ADC_DelSig (44ksps). 


      uint8 adc_bufferArray1[4000]={0};
      uint8 adc_bufferArray11[4000]={0};


      DMA_2 is configured as a chain of TDs (advanced by the same ADC_DelSig EOC) to transfer a new byte from the circular buffer to a VDAC but with an offset starting point to cause a delayed output.


      The goal is to control this offset with a variable to change the delay time. 


      I've almost wrapped my head around how to change DMA_2's starting TD with a variable giving 10 or 11 different delay times. In the meantime priority is given to DMA_1 to avoid conflicts, although I think there's a way to track this with a counter/status register or something.


      My question: is there a way, using DMA, to vary the starting TD and the byte in that particular source with a variable?


      (I have the variable obtained and scaled via SAR_ADC and a potentiometer.)


      Thank you in advance for any wisdom you may offer and the time to articulate it!!! I've been reading your posts for months and really appreciate your guidance and ideas.

        • 1. Re: Accessing variable starting points in an array with DMA

          I don't think you can change the order of the TDs dynamically but you can change the pointer into your Array. Rather than have the TD point to a specific Array or Array element, have its output directed to a pointer pA[0] or elsewhere. You can change the pointer prior to each call of the TDs.


          for example:
          #define LENGTH 4000
          #define NUM_TDs 11
          uint16 *pA[NUM_TDs]; // an array of pointers

          void set_pointers()  // Sets the pointers to the output arrays
              uint16 j;
              for (j = 0; j < NUM_TDs; j++)
                  pA[j] = &(adc_bufferArray[some offset value here wherever you want to point]);


          Then let your TD use these pointers:


          CyDmaTdSetAddress(adc_bufferArray[0], LO16((uint32)&sar_finalArray[0]), LO16((uint32) pA[0]));