How to change NDTR after enabling DMA stream?

[YoungKim]

I can want to change NDTR after enabling DMA stream. but I can't. This is the part of code

...
    LL_DMA_EnableStream(DMA1, LL_DMA_STREAM_5);
    // works fine now
    // but I want to change the data length only
 
    LL_DMA_SetDataLength(DMA1, LL_DMA_STREAM_5, 11); // this doesn't work 
 
    LL_DMA_DisableStream(DMA1, LL_DMA_STREAM_5);
    LL_DMA_SetDataLength(DMA1, LL_DMA_STREAM_5, 12); // this works
    LL_DMA_EnableStream(DMA1, LL_DMA_STREAM_5); // but this doesn't work !!

I checked the result in SFRs of debugger.

[waclawek.jan]

Which STM32?

You can't change NDTR while stream is enabled. You can change it when stream is disabled, but that also restarts the internal memory/peripheral pointers, that's probably what confused you.

JW

[YoungKim]

It is STM32F767.

I can see the stream is enabled in debugger after add the block of code below:

   /* Enable DMA Channels */
 
   LL_DMA_EnableStream(DMA1, LL_DMA_STREAM_5);
 
 
 
   {
 
       LL_DMA_DisableStream(DMA1, LL_DMA_STREAM_5);
 
       LL_DMA_SetPeriphAddress(DMA1, LL_DMA_STREAM_5, LL_USART_DMA_GetRegAddr(USART2, LL_USART_DMA_REG_DATA_RECEIVE));
 
       LL_DMA_SetMemoryAddress(DMA1, LL_DMA_STREAM_5, (uint32_t)servoDmaRxBuffer);
 
       LL_DMA_SetDataLength(DMA1, LL_DMA_STREAM_5, 30);
 
 
 
       LL_DMA_EnableStream(DMA1, LL_DMA_STREAM_5);
 
   }

But It doesn't generate DMA interrupt if I add this block.

DMA interrupt works find if I remove the block.

[waclawek.jan]

To disable/enable stream, follow procedure prescribed by RM.

After clearing CR.EN, read it back and wait until it reads zero. Then, before setting it again, clear the status flags.

JW

[YoungKim]

Thanks JW. It works now. I should have read the RM more carefully.