DMA : Timer Trigger Memory-to-memory mode,

The DMA channels can also work without being triggered by a request from a peripheral.

This mode is called Memory to Memory mode.

If the MEM2MEM bit in the DMA_CCRx register is set, then the channel initiates transfers

as soon as it is enabled by software by setting the Enable bit (EN) in the DMA_CCRx register."

// STM32 TIM2 DMA Mem-to-Mem pacing VLDiscovery - sourcer32@gmail.com

#include "STM32vldiscovery.h"

#define OUTLENGTH 5

volatile u16 InBuffer[OUTLENGTH], OutBuffer[OUTLENGTH];

/**************************************************************************************/

void RCC_Configuration(void)
{
    // clock for DMA
    RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA1, ENABLE);

    // clock for TIM2
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
}

/**************************************************************************************/

void NVIC_Configuration(void)
{
    NVIC_InitTypeDef NVIC_InitStructure;

    NVIC_PriorityGroupConfig(NVIC_PriorityGroup_1);

  NVIC_InitStructure.NVIC_IRQChannel = DMA1_Channel2_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = ;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = ;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);
}

/******************************************************************************/

void DMA1_Channel2_IRQHandler(void) // Called at 10 Hz
{
  if (DMA_GetITStatus(DMA1_IT_TC2))
  {
    DMA_ClearITPendingBit(DMA1_IT_TC2);

    STM32vldiscovery_LEDToggle(LED3); // Toggle 5 Hz
    STM32vldiscovery_LEDToggle(LED4);

    // Do something
  }
}

/**************************************************************************************/

void DMA_Configuration(void)
{
    DMA_InitTypeDef DMA_InitStructure;

    DMA_DeInit(DMA1_Channel2);

    DMA_InitStructure.DMA_PeripheralBaseAddr = (u32)&InBuffer[]; // Source
    DMA_InitStructure.DMA_MemoryBaseAddr = (u32)&OutBuffer[];  // Destination
    DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;
    DMA_InitStructure.DMA_BufferSize = OUTLENGTH;
    DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Enable;
    DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
    DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
    DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
    DMA_InitStructure.DMA_Mode = DMA_Mode_Circular; // Repetitive, for my convenience
    DMA_InitStructure.DMA_Priority = DMA_Priority_High;
    DMA_InitStructure.DMA_M2M = DMA_M2M_Disable; // So we can pace via trigger
    DMA_Init(DMA1_Channel2, &DMA_InitStructure);

    /* Enable DMA1 Channel2 Transfer Complete interrupt */
    DMA_ITConfig(DMA1_Channel2, DMA_IT_TC, ENABLE);

    // turning DMA on (DMA1 Channel2 -> TIM2_UP)
    DMA_Cmd(DMA1_Channel2, ENABLE);
}

/**************************************************************************************/

void TIM2_Configuration(void)
{
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

    TIM_TimeBaseStructure.TIM_Prescaler = (SystemCoreClock / ) - ;  // 1 MHz
    TIM_TimeBaseStructure.TIM_Period = -; // 1MHz/20000 = 50 Hz
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseStructure.TIM_RepetitionCounter = ;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

    // "connecting" DMA and TIM2
    TIM_DMACmd(TIM2, TIM_DMA_Update, ENABLE);

    // turning on TIM2
    TIM_Cmd(TIM2, ENABLE);
}

/**************************************************************************************/

int main(void)
{
  /* Initialise LEDs LD3 & LD4 */
  STM32vldiscovery_LEDInit(LED3);
  STM32vldiscovery_LEDInit(LED4);

  STM32vldiscovery_LEDOn(LED3);
  STM32vldiscovery_LEDOff(LED4);

  RCC_Configuration();

  NVIC_Configuration();

  DMA_Configuration();

  TIM2_Configuration();

  while();
}