SPI and DMA on STM32F2xx

[carl2399]

Posted on November 23, 2011 at 02:23

Is there a simple example of this?

I've written some code based on a working non-DMA version of my SPI object. So far I have the following:void SPI2_StartDMA(u16 NumBytes){ // Disable both DMA channels DMA1_Stream3->CR   &= ~1; DMA1_Stream4->CR   &= ~1; // Disable the SPI port SPI2->CR1          &= ~0x40; // Clear any outstanding DMA interrupts DMA1->LIFCR         = 0x0F400000; DMA1->HIFCR         = 0x0000003D; // Configure the receiver DMA1_Stream3->CR    = (DMA1_Stream3->CR & 0xF0100000) | 0x00012C20; DMA1_Stream3->NDTR  = NumBytes; DMA1_Stream3->PAR   = (uint32_t)&(SPI2->DR); DMA1_Stream3->M0AR  = (uint32_t)&(SPI2RxBuf[0]); // Configure the transmitter DMA1_Stream4->CR    = (DMA1_Stream4->CR & 0xF0100000) | 0x00012C60; DMA1_Stream4->NDTR  = NumBytes; DMA1_Stream4->PAR   = (uint32_t)&(SPI2->DR); DMA1_Stream4->M0AR  = (uint32_t)&(SPI2TxBuf[0]); // Flush the SPI receiver (void)SPI2->DR; // Enable the DMA mode in the SPI SPI2->CR2          |= 3; // Enable the DMA devices     DMA1_Stream3->CR   |= 1; DMA1_Stream4->CR   |= 1; // Enable the SPI Port - to start the transfer SPI2->CR1          |= 0x40; }I call the previous function with something like: SPI2TxBuf[0] = 10; SPI2TxBuf[1] = 0; SPI2TxBuf[2] = 55;

SPI2_StartDMA(3); // Tx/Rx 3 bytes // Wait for the received response

printf(''Wait.'');

while ((DMA1->LISR & 0x0B400000) == 0) ;

printf(''Success.'');

I get ''Wait.'', but no ''Success.''. It's like the process hasn't started.

Any ideas as to what I might be doing wrong?

[loeffel2]

Posted on November 23, 2011 at 08:13

Hi

Did you setup your SPI to support DMA for transmitting and receiving? Is the receiver FIFO setup correct? Regards Raphael  

[carl2399]

Posted on November 23, 2011 at 08:41

Hi Raphael,

In answer to your questions, the code I attached includes:

// Enable the DMA mode in the SPI

SPI2->CR2          |= 3;

and

DMA1_Stream3->M0AR  = (uint32_t)&(SPI2RxBuf[0]);

...

DMA1_Stream4->M0AR  = (uint32_t)&(SPI2TxBuf[0]);

Which I believe answers both your questions.

SPI2RxBuf[0] and 

SPI2TxBuf[0] are defined as simple arrays.

I know the SPI port works, because my port-bashed non-DMA version of the driver works fine. 

[carl2399]

Posted on November 23, 2011 at 12:08

Solved.

In the end it was a simple misunderstanding of the role of peripheral control versus DMA control of the flow controller. The solution was to change the following lines:

DMA1_Stream3->CR    = (DMA1_Stream3->CR & 0xF0100000) | 0x00012C00;

...

DMA1_Stream4->CR    = (DMA1_Stream4->CR & 0xF0100000) | 0x00012C40;

Blink and you'll miss the change. But making this change resulted in the DMA jumping into life!This processor is so cool - even if a bit mind-numbing at times.