Accessing data stored in DMA memory by USART

[waleedaslam89]

Posted on July 11, 2012 at 13:55

Hello ,

I am new to STM32. I am reading data from USART using DMA. I dont know how to directly access data from DMA memory after transfer complete interrupt.

[Tesla DeLorean]

Posted on July 11, 2012 at 14:53

Just like any other memory. Use pointers or array access.

If you passed &Buffer to the DMA controller as the transfer address, then Buffer[i]

[waleedaslam89]

Posted on July 12, 2012 at 06:29

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[Tesla DeLorean]

Posted on July 12, 2012 at 11:47

uint8_t *BufferStart = (uint8_t *)0x20004000; // An Address in RAM

uint32_t BufferSize = 10240;

..

DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)BufferStart;

DMA_InitStructure.DMA_BufferSize = (uint16_t)BufferSize;

..

for(i=0; i<BufferSize; i++)

 sum += BufferStart[i];

Although I can't see why you couldn't statically allocate the buffer.

[waleedaslam89]

Posted on July 12, 2012 at 12:54

Thanks for your reply,

Actually i am confused in a little bit different manner. For example if I give this Address (e.g 0x20004000) to DMA to start writing from here, and if in my code there are many local functions that create random variables , so is it possible that DMA may corrupt these variables (because DMA only knows the starting address and buffer size ). 

Pls clarify me in this regard.

 

[Tesla DeLorean]

Posted on July 12, 2012 at 15:18

Which is why most of us would statically allocate such buffers, or carve out some space by modifying the linker script or scatter file.