5Channel ADC -- DMA triggered by timer to achieve lower sample rates: Do I need to restart DMA or ADC? When does HAL_ADC_ConvCpltCallback get triggered?

Question

Posted on November 01, 2017 at 23:01Need to sample 5 channels at 20Hz.  Would like an interrupt when the DMA buffer is filled (50 samples).  Waiting on boards to arrive and have a few questions:1) Does the ADC or DMA needs restarted after each conversion of the sequence (5 channels) when set to trigger off a timer with continuous disabled (i.e. HAL_ADC_Start_IT)?  I'm thinking no.2) When triggering ADC conversion off a timer using DMA, when is HAL_ADC_ConvCpltCallback called?  Is it after the 5 channels are sampled once or the DMA buffer is full? Is it after the 5 channels are sampled once or the DMA buffer is full? I've seen examples using continuous ADC mode where HAL_ADC_ConvCpltCallback is called when the DMA buffer is full.   I've also seen examples do not use DMA where HAL_ADC_ConvCpltCallback is called after each conversion.  Are these both true (depending on whether you are using DMA?).  In the end, I want a call back when the buffer is full so that I can retrieve n samples.MCU: STM32F071CBADC Continuous mode: disabledTriggered off: ADC_EXTERNALTRIGCONV_T1_TRGOConfiguration details below.  Also see attached wrapper for initializing the ADC, DMA, and TIMThank you in advance for your help.//ADC Configuration    adcHandle.Instance                   = ADC_HANDLE;    adcHandle.Init.ClockPrescaler        = ADC_CLOCK_SYNC_PCLK_DIV2;    //HSI14 Not divisible    adcHandle.Init.Resolution            = ADC_RESOLUTION_12B;    adcHandle.Init.DataAlign             = ADC_DATAALIGN_RIGHT;    adcHandle.Init.ScanConvMode          = ADC_SCAN_DIRECTION_FORWARD;    adcHandle.Init.EOCSelection          = ADC_EOC_SEQ_CONV;            //Read as group of channels    adcHandle.Init.LowPowerAutoWait      = DISABLE;    adcHandle.Init.LowPowerAutoPowerOff  = DISABLE;                     //HSI14 powers off between conversions    adcHandle.Init.ContinuousConvMode    = DISABLE;                     //Perform conversion until overrun    adcHandle.Init.DiscontinuousConvMode = DISABLE;               adcHandle.Init.ExternalTrigConv      = ADC_EXTERNALTRIGCONV_T1_TRGO;      //Conversion triggered by timer    adcHandle.Init.ExternalTrigConvEdge  = ADC_EXTERNALTRIGCONVEDGE_RISING;  //trigger on rising edge    adcHandle.Init.DMAContinuousRequests = ENABLE;                      //DMA    adcHandle.Init.Overrun               = ADC_OVR_DATA_OVERWRITTEN;    //Old data is overwritten    adcHandle.Init.SamplingTimeCommon    = PRESSURE_OVERSAMPLE_RATE_CYCLES;  //Oversampling rateDMA//Enable DMA clock    PRESSURE_DMA_CLOCK();        //Configure DMA    adcDmaHandle.Instance                 = PRESSURE_DMA_CHANNEL;    adcDmaHandle.Init.Direction           = DMA_PERIPH_TO_MEMORY;    adcDmaHandle.Init.PeriphInc           = DMA_PINC_DISABLE;         //use the same peripheral address    adcDmaHandle.Init.MemInc              = DMA_MINC_ENABLE;          //increment after each conversion    adcDmaHandle.Init.PeriphDataAlignment = DMA_PDATAALIGN_HALFWORD;  //two bytes per sample    adcDmaHandle.Init.MemDataAlignment    = DMA_MDATAALIGN_HALFWORD;  //two bytes per sample    adcDmaHandle.Init.Mode                = DMA_CIRCULAR;             //do not use circular buffer    adcDmaHandle.Init.Priority            = DMA_PRIORITY_VERY_HIGH;   //Only one DMA channel, so moot setting        //Deinitialize, then initialize the DMA    HAL_DMA_DeInit(&adcDmaHandle); //function always returns HAL_OK     HAL_DMA_Init(&adcDmaHandle);   //function always returns HAL_OK         //NVIC configuration for DMA Input data interrupt    /*Set pre-emptive priority to 0 (highest) as per CubeMx Example        Note that subpriority is not available on M0 device... set to 0.*/        HAL_NVIC_SetPriority(PRESSURE_DMA_IRQ, PRESSURE_DMA_PREEMPT_PRIORITY, 0);     HAL_NVIC_EnableIRQ(PRESSURE_DMA_IRQ);          //Associate the DMA handle    __HAL_LINKDMA(&adcHandle, DMA_Handle, adcDmaHandle);TimerTIM_MasterConfigTypeDef adcTimConfig;        //Enable timer clock    PRESSURE_START_TIMER_CLK();        //Configure Timer    adcTimHandle.Instance               = PRESSURE_START_TIMER;    adcTimHandle.Init.Period            = PRESSURE_TIMER_PERIOD_CYCLES;    adcTimHandle.Init.Prescaler         = PRESSURE_TIMER_PRESCALER;    adcTimHandle.Init.ClockDivision     = PRESSURE_TIMER_CLOCK_DIV;    adcTimHandle.Init.CounterMode       = TIM_COUNTERMODE_DOWN;    adcTimHandle.Init.RepetitionCounter = 0;  //not used (counts reps as way to slow down the timer even further)    adcTimHandle.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE; //disable changing reload on the fly        errorCodeHal = HAL_TIM_Base_Init(&adcTimHandle);    //Set timer to trigger on over/underflow */    if(HAL_OK == errorCodeHal)    {        adcTimConfig.MasterOutputTrigger = TIM_TRGO_UPDATE;  //Triggers on under/overflow        adcTimConfig.MasterSlaveMode     = TIM_MASTERSLAVEMODE_DISABLE;                errorCodeHal = HAL_TIMEx_MasterConfigSynchronization(&adcTimHandle, &adcTimConfig);    }

Tesla DeLorean · Answer

Posted on November 01, 2017 at 23:37At each trigger event 5 samples will be taken, you can make the buffer for 50 or 100 samples deep, and use circular DMA. These things are initialized once and done, and if you use the HT/TC DMA interrupts you can manage half the buffer without worries of the data changing underneath you.I wouldn't use HAL, that's your choice to make.

5Channel ADC --> DMA triggered by timer to achieve lower sample rates: Do I need to restart DMA or ADC? When does HAL_ADC_ConvCpltCallback get triggered?

4 replies

Sign up

Login with SSO

Login to the community

Login with SSO