Posted on March 16, 2015 at 23:11OK, so I get that DMA buffer has a limit but I totally dont get how is the transfer driven...The code below is from two diferent versions of the SW...It's not together but I think it's a good example so I just want to explanation how is the DMA behaving...
When I want to copy data from DCMI (32 bit register) to some kind of frame buffer (16 bit array uint16_t frame_buffer[320*240]) then buffer size 38400 is enough and it works well. Then I woud say, yeah the increment is driven by the DCMI register that is 32bit.
DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t) (&DCMI->DR);
DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t) frame_buffer;
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;
DMA_InitStructure.DMA_BufferSize = 320*240*2/4;
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Word; DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
But when I want to for example copy data from SDRAM to SPI for transfer. Now if I follow the same logic because the source is 32 bit than 38400 sould also be enough. But it's not... buffer size 38400 makes only 1/4 od the image...why is now the transfer driven by individual bytes therefore I would need 4*38400= 153600??
DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t) p_img;
DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t) &(ILI9341_SPI->DR);
DMA_InitStructure.DMA_DIR = DMA_DIR_MemoryToPeripheral;
DMA_InitStructure.DMA_BufferSize = 320*240*2/4;
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Word;
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;
