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MSPM0G3507: Continuous ADC Sampling with DMA transfer

toby
Prodigy 50 points

Part Number: MSPM0G3507

Hi TI team,

I try to do a Continuous ADC Sampling with DMA transfer. I need 1024 samples/s. The Sample Time 0 is set to 976.56us (1/1024). As example I modified the adc12_max_freq_dma. The conversion started only once. But with the setting 'Enable Repeat Mode' it should restart. What is the reason for this?

#include "ti_msp_dl_config.h"

#define ADC_SAMPLE_SIZE (1024)
/* When FIFO is enabled 2 samples are compacted in a single word */
#define ADC_FIFO_SAMPLES (ADC_SAMPLE_SIZE >> 1)

uint16_t gADCSamples[ADC_SAMPLE_SIZE];
volatile bool gCheckADC;

int main(void)
{
    SYSCFG_DL_init();

    /* Configure DMA source, destination and size */
    DL_DMA_setSrcAddr(DMA, DMA_CH0_CHAN_ID,
        (uint32_t) DL_ADC12_getFIFOAddress(ADC12_0_INST));

    DL_DMA_setDestAddr(DMA, DMA_CH0_CHAN_ID, (uint32_t) &gADCSamples[0]);
    DL_DMA_setTransferSize(DMA, DMA_CH0_CHAN_ID, ADC_FIFO_SAMPLES);

    DL_DMA_enableChannel(DMA, DMA_CH0_CHAN_ID);

    /* Setup interrupts on device */
    NVIC_EnableIRQ(ADC12_0_INST_INT_IRQN);

    gCheckADC = false;

    DL_ADC12_startConversion(ADC12_0_INST);

    while (1) {

        while (false == gCheckADC) {
            __WFE();
        }
        gCheckADC = false;
        DL_GPIO_togglePins(GPIO_LEDS_PORT, GPIO_LEDS_USER_LED_1_PIN);
        delay_cycles(1600000); 
        DL_GPIO_togglePins(GPIO_LEDS_PORT, GPIO_LEDS_USER_LED_1_PIN);
    }
}

void ADC12_0_INST_IRQHandler(void)
{
    switch (DL_ADC12_getPendingInterrupt(ADC12_0_INST)) {
        case DL_ADC12_IIDX_DMA_DONE:
            gCheckADC = true;
            DL_DMA_enableChannel(DMA, DMA_CH0_CHAN_ID);
            DL_ADC12_enableConversions(ADC12_0_INST); 
            break;
        default:
            break;
    }
}

image.pngimage.pngimage.png

  • 0
    TI__Mastermind 22577 points

    Make sure the trigger will automatically step ... is selected.

    1024/6 = 170...4, you will get 4 ADC result left in ADC FIFO when 1020 result finished.

    Recommend to set ADC sample count to 5

  • 0 in reply to Helic Chi
    Prodigy 50 points

    yes it is


    And 1024/16=64
    Is there any disadvantage?

  • 0 in reply to toby
    TI__Mastermind 22577 points
    toby said:
    And 1024/16=64
    Is there any disadvantage?

    No, there is no 32 * 16 bit memory in ADC, so you can set such large value in DMA sample count.

    It's better to set DMA sample count = 1, and enable 1,3,5,7,9,11's MEM trigger (trigger DMA to transfer every two ADC result)

    Or

    It's better to set DMA sample count = 2, and enable 3,7,11's MEM trigger (trigger DMA to transfer every 4 ADC result)

  • 0 in reply to Helic Chi
    Prodigy 50 points

    If I understand this, 12 samples can be saved in the ADC memory.

    But why isn't the sampling continuing?

  • 0 in reply to Helic Chi
    Prodigy 50 points

    Hi, thanks for this example. I have some questions to understand it. Please correct my statements if they are wrong.

    - Sample Time 0 and 1 is set to 40us which results at 32MHz clock to a CCR value of 1280.
    - I think only sample time 0 is necessary
    - every 1280 clock cycles 1 ADC sample is aquired
    - Interrupt DL_ADC12_IIDX_DMA_DONE occurs if 1024 samples are aquired and saved in user variable gADCSamples

    - is this necessary and why 6? Is this the DMA Memory which size of 12 elements?

    // Clear ADC FIFO Data
for(int i = 0; i < 6; i++) {
DL_ADC12_getFIFOData(ADC12_0_INST);
}


    - ADCGroupCount only stops the code after 10x1024 samples, no other sense (?)
    - Delay Cycles between the groups - why?
    - Implementation TimerA? Sample time 0 has a ccr of 1280 and not 255. What is the sense of TimerA?

  • 0 in reply to toby
    TI__Mastermind 22577 points
    toby said:
    - I think only sample time 0 is necessary

    I only use this sample time 0, 1 is not in use.

    toby said:
    - every 1280 clock cycles 1 ADC sample is aquired

    No, use timer to trigger ADC to start, ADC samples for 40us, then conversion.

    toby said:
    - Interrupt DL_ADC12_IIDX_DMA_DONE occurs if 1024 samples are aquired and saved in user variable gADCSamples

    Yes.

    toby said:
    - is this necessary and why 6? Is this the DMA Memory which size of 12 elements?

    Please remove this part of for loop code, this is my previous debug code to clear the ADC fifo.

    toby said:
    - ADCGroupCount only stops the code after 10x1024 samples, no other sense (?)

    You can stop at any ADC groups, 10 is my debug setting.

    toby said:
    - Delay Cycles between the groups - why?

    You can delete it.

    toby said:
    - Implementation TimerA? Sample time 0 has a ccr of 1280 and not 255. What is the sense of TimerA?

    use timer to trigger ADC to start, ADC samples for 40us, then conversion.

    Event is used between ADC and timer.

  • 0 in reply to Helic Chi
    Prodigy 50 points

    What settings I need with your example to get 1024 samples per second?

  • 0 in reply to toby
    TI__Mastermind 22577 points

    No change.

    I already set my code sampling rate = 1024 SPS.

    You can test it with some GPIO toggle in free run mode.

    Next following week is Chinese New year, if there is urgent support need, please submit a new ticket.

  • 0 in reply to Helic Chi
    Prodigy 50 points

    Ok, but for understanding:

    - for 1024S/s I need a sample rate of (1/1024)s=976.5625us not 40us?

    - Sample time 0 ist 1280 (40us at 32MHz), why not 31250 (1/1024 / 1/32MHz) for Sample time 0 ?

    - And why 255 for Timer 0? Timer 0 has in your example initial value of 1280...

  • 0 in reply to toby
    Prodigy 50 points

    And which ADC Channel and Pin is used. I recognize an ADC1 setting. But which pin I can connect for signal input tests? There isn't a pin selection.

  • 0 in reply to toby
    TI__Mastermind 22577 points

    nonono, I am using timer 1024hz

     to trigger ADC.

    You can select ADC input in ADC memory

    Input mix info can get from datasheet chapter 8 ADC section