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Refinement about DMA

Question asked by Roman K on Feb 28, 2018
Latest reply on Mar 2, 2018 by avi_crak.videocrak

I have a few misunderstandings about DMA, so I need some help. 

I setup DMA to copy from GPIO IDR (without inc) to sram (with inc), it triggered from Timer (Free Running, Overflow event).

In the case of algorithm like following:

   1. DMA setup

   2. Timer Start

   3. Infinite Loop

   4. Breakpoint in DMA Interrupt handler

All works fine, program jumps into interrupt handler, the sram buffer is filled up with some data from IDR. But when I change an algorithm like that:

   1. DMA setup

   2. Timer Start

   3.1. WFI (I'm using an assembler)

   3.2. Infinite Loop

   4. Breakpoint in DMA Interrupt handler

The interrupt wakes core up, but the buffer is empty (not changed). DMA CNDTR register is 0 and there are no error flags. In Reference Manual I have this about WFI: "CPU clock OFF, no effect on other clocks or analog clock sources", so, what did I miss? And how should I "wait" for DMA interrupt without entering in checking loop?


Another misunderstanding: I want to read least significant byte of IDR, so, I setup PSIZE = 16bits (as it said in Reference Manual "IDR can be accessed in Word mode only"), MSIZE = 8bits (like in Table 76 in Reference Manual). But sram is filled with halfwords anyway (doesn't matter what values of PSIZE (16bits/8bits) and MSIZE (16bits/8bits) are).


And some stupid misunderstanding: why can't I use source address of DMA in peripheral bit-band region as peripheral (to read specified GPIO bit)?