Example for SSP1/GPDMA transfer at Cortex-M3 (LPC1787)

Question

I try to utilize the GPDMA controller to access the SSP1 channel. Using the CMSIS library this should be comprehensive. But I can't see anything at the SSP1 output.

As a first example I want to send one byte.

uint8_t buffer[20] = { 0x9F };

int main(void)
{
  // ... using PINSEL_ConfigPin to configure the SSP1 pins...

  // configure SSP
  SSP_CFG_Type ssp_config;
  ssp_config.Databit = SSP_DATABIT_8;
  ssp_config.CPHA = SSP_CPHA_SECOND;
  ssp_config.CPOL = SSP_CPOL_LO;
  ssp_config.Mode = SSP_MASTER_MODE;
  ssp_config.FrameFormat = SSP_FRAME_SPI;
  ssp_config.ClockRate = 4500000;

  SSP_Init(LPC_SSP1, &ssp_config);
  SSP_Cmd(LPC_SSP1, ENABLE);

  // configure GPDMA
  GPDMA_Channel_CFG_Type dma_config;

  dma_config.ChannelNum = GPDMA_CONN_SSP1_Tx;
  dma_config.TransferSize = 1;                   // <-- (A)
  dma_config.TransferWidth = 0; // M2M only
  dma_config.SrcMemAddr = (uint32_t)&buffer[0];
  dma_config.DstMemAddr = 0;
  dma_config.TransferType = GPDMA_TRANSFERTYPE_M2P;
  dma_config.SrcConn = 0;
  dma_config.DstConn = GPDMA_CONN_SSP1_Tx;
  dma_config.DMALLI = 0;

  Status status = GPDMA_Setup(&dma_config);

  // (B) this was just a try
  LPC_SC->DMAREQSEL |= (1 << dma_config.DstConn);

  // now start DMA
  GPDMA_ChannelCmd(4, ENABLE);
}

Annotations: (A) I varied the size: 0, 1, 20, several value nothing changes (B) The CMSIS implementation always resets the bits in the DMAREQSEL register. Since I think the must be set, I added this line. But the result doesn't change.

When I use the SSP polling function that directly reads/writes the LPC_SSP1 registers I can see the transfer at the logic analyzer. But nothing happens when the GPDMA is used. What's wrong with the approach?

Is there a working example out there?

Answer 1

The setup was incomplete. While the DMA is ready to transfer the SSP interface must enable the DMA access.

This line before the end of the function makes it work:

SSP_DMACmd(LPC_SSP1, SSP_DMA_TX, ENABLE);