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First attempt at SPI DMA not working

Question asked by Mr. Blinky on Aug 7, 2013
I've lurked for quite some time and learned a ton but am stumped on this one and can't find a solution.  I'm new to ARM (8-bit AVR convert) and I'm afraid something simple is escaping me on this one.  I've got a fully functional blocking SPI version of my code sending data to an LED strip.  However, upgrading it to DMA has proven a challenge (my first time using DMA).  I've hooked up my logic analyzer and confirmed that there is absolutely no activity on SCK/MOSI with the code below when calling the DMA_beginWrite().  Any ideas why?

PS - My code was more/less ported from the example here (though he's using SPI2 and of course DMA1): http://www.micromouseonline.com/2012/03/11/adding-dma-to-the-spi-driver-with-the-stm32f4/#axzz2bESa5DIM

void DMA_init()
{
  //Start with a fresh DMA config
  DMA_InitTypeDef DMA_InitStructure;
  DMA_DeInit(DMA2_Stream3);
  DMA_StructInit(&DMA_InitStructure);
 
  //Enable the clock
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2, ENABLE);
 
  //Setup SPI DMA for TX
  DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t) &(SPI1->DR);
  DMA_InitStructure.DMA_Channel = DMA_Channel_3;
  DMA_InitStructure.DMA_DIR = DMA_DIR_MemoryToPeripheral;
  DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
  DMA_InitStructure.DMA_Memory0BaseAddr = 0;      //Setting only needed to suppress in case assert macro is active
  DMA_InitStructure.DMA_BufferSize = 1;           //Setting only needed to suppress in case assert macro is active
  DMA_Init(DMA2_Stream3, &DMA_InitStructure);
  DMA_ITConfig(DMA2_Stream3, DMA_IT_TC, ENABLE);
 
  //Setup interrupt for completed DMA transfers
  NVIC_InitTypeDef NVIC_InitStructure;
  NVIC_InitStructure.NVIC_IRQChannel = DMA2_Stream3_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_Init(&NVIC_InitStructure);
  SPI_I2S_DMACmd(SPI1, SPI_I2S_DMAReq_Tx, ENABLE);    //Enable DMA TX request
}
 
void SPI_PORT_DMA_TX_IRQHandler()
{
  //DMA stream transfer complete?
  if (DMA_GetITStatus(DMA2_Stream3, DMA_IT_TCIF4))
  {
    DMA_ClearITPendingBit(DMA2_Stream3, DMA_IT_TCIF4);
    while (SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_TXE) == RESET) { };
    while (SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_BSY) == SET) { };
   }
}
 
void DMA_beginWrite()
{
  DMA2_Stream3->NDTR = (uint32_t) sizeof(_pixelData);
  DMA2_Stream3->M0AR = (uint32_t) _pixelDataPtr;
  DMA_Cmd (DMA2_Stream3, ENABLE);
}
 
void SPI_init()
{
  //Enable clock for GPIOA
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
 
  //Configure GPIO pins for SPI1 (PA5=SCK, PA7=MOSI)
  GPIO_InitTypeDef GPIO_InitStruct;
  GPIO_InitStruct.GPIO_Pin = GPIO_Pin_7 | GPIO_Pin_5;
  GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStruct.GPIO_Speed = GPIO_Speed_2MHz;
  GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_Init(GPIOA, &GPIO_InitStruct);
 
  // connect SPI1 pins to SPI alternate function
  GPIO_PinAFConfig(GPIOA, GPIO_PinSource5, GPIO_AF_SPI1);
  GPIO_PinAFConfig(GPIOA, GPIO_PinSource7, GPIO_AF_SPI1);
 
 
  // enable peripheral clock
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1, ENABLE);
 
  /* configure SPI1 in Mode 0
   * CPOL = 0 --> clock is low when idle
   * CPHA = 0 --> data is sampled at the first edge
   */
  SPI_InitTypeDef SPI_InitStruct;
  SPI_InitStruct.SPI_Direction = SPI_Direction_1Line_Tx; // set to TX only (MOSI used)
  SPI_InitStruct.SPI_Mode = SPI_Mode_Master;     // transmit in master mode, NSS pin has to be always high
  SPI_InitStruct.SPI_DataSize = SPI_DataSize_8b; // one packet of data is 8 bits wide
  SPI_InitStruct.SPI_CPOL = SPI_CPOL_Low;        // clock is low when idle
  SPI_InitStruct.SPI_CPHA = SPI_CPHA_1Edge;      // data sampled at first edge
  SPI_InitStruct.SPI_NSS = SPI_NSS_Soft; // set the NSS management to internal and pull internal NSS high
  SPI_InitStruct.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_64; // SPI frequency is APB2 frequency / 2
  SPI_InitStruct.SPI_FirstBit = SPI_FirstBit_MSB;// data is transmitted MSB first
  //SPI_InitStruct.SPI_CRCPolynomial = 0;     //No CRC used
  SPI_Init(SPI1, &SPI_InitStruct);
 
  SPI_Cmd(SPI1, ENABLE); // enable SPI1 
}
 
void SPI_write(uint8_t data)
{
    while( !(SPI1->SR & SPI_I2S_FLAG_TXE) ); // wait until transmit complete
    SPI1->DR = data; // write data to be transmitted to the SPI data register
}

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