Posted on May 17, 2011 at 13:07I want to receive 48bit blocks of data using the STM32 as a SPI slave. The following code works fine:
(SPI2_DR_Address=SPI data register,SPI_RxBuffer_size=6
[...]
DMA_InitStructure.DMA_PeripheralBaseAddr = (u32)SPI2_DR_Address;
DMA_InitStructure.DMA_MemoryBaseAddr = (u32)g_SPI_RxBuffer.list;
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralSRC;
DMA_InitStructure.DMA_BufferSize = SPI_RxBuffer_size;
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;
DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;
DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;
DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;
DMA_Init(DMA1_Channel4, &DMA_InitStructure);
SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
SPI_InitStructure.SPI_Mode = SPI_Mode_Slave;
SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;
SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;
SPI_InitStructure.SPI_NSS = SPI_NSS_Hard;
SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_LSB;
SPI_Init(SPI2, &SPI_InitStructure);
[...]
But I think it's rather inefficient as there are six bus accesses.
I tried to change it to the the following:
[...]
DMA_InitStructure.DMA_BufferSize = 3;
[...]
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
[...]
SPI_InitStructure.SPI_DataSize = SPI_DataSize_16b;
[...]
Should only need three accesses, but instead of the real data, I only received zeroes...
Any reasons or ideas for that strange behaviour?
