Another question about SPI and DMA

Posted on May 17, 2011 at 13:08

I am trying to read a block of data from a flash memory device

into the STM32 using SPI and DMA. What I noticed on the

o-scope is that when I write the command, 24-address, and dummy-byte

there is a clock from the MCU (SPI master mode). After

the last control byte (dummy) is sent, the read data is supposed

to be clocked back into the STM32 but I don't see any clock pulses.

I have the SPI device configured for DMA and the DMA engine

configured for the number of bytes to read. I never see

any data transferred though.

Here is my config:

/* SPI2 configuration */

SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;

SPI_InitStructure.SPI_Mode = SPI_Mode_Master;

SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;

SPI_InitStructure.SPI_CPOL = SPI_CPOL_High;

SPI_InitStructure.SPI_CPHA = SPI_CPHA_2Edge;

SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;

SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_2;

SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;

SPI_InitStructure.SPI_CRCPolynomial = 7;

SPI_Init(SPI2, &SPI_InitStructure);

DMA_DeInit(DMA_Channel1);

DMA_InitStructure.DMA_PeripheralBaseAddr = (u32)&(SPI2->DR);

DMA_InitStructure.DMA_MemoryBaseAddr = (u32)dma;

DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;

DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;

DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;

DMA_InitStructure.DMA_BufferSize = 128;

DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;

DMA_InitStructure.DMA_MemoryDataSize = DMA_PeripheralDataSize_Byte;

DMA_InitStructure.DMA_Mode = DMA_Mode_Normal;

DMA_InitStructure.DMA_Priority = DMA_Priority_High;

DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;

DMA_Init(DMA_Channel1, &DMA_InitStructure);

// Enable DMA channel1

DMA_Cmd(DMA_Channel1, ENABLE);

// tell the spi to use DMA

SPI_DMACmd(SPI2, SPI_DMAReq_Rx, ENABLE);

// enable spi device

SPI_Cmd(SPI2, ENABLE);

Any ideas how to get that clock to toggle?

Victor

Posted on May 17, 2011 at 13:08

DMA doesn't know that clock must be generated. It just waits for flag that received data arrived.

You must setup another channel for transmiting dummy data. Be careful with channel index (there is a table of available channels for SPI TX and SPI RX in reference manual) and enable sequence: enable RX first, then TX.

[ This message was edited by: slawcus on 06-04-2009 08:31 ]