Timer -> DMA -> SPI

[Dude]

Hi, 

    I am having trouble getting the Timer to trigger a DMA -> SPI operation. Namely, I want to set the timer up to run,. Then, get every overflow event to trigger the DMA to move a byte into the SPI. The SPI should auto-send. Then, the cycle repeats until the DMA has moved a N-bytes. 

I am feeling really blind, because I cannot figure out the problem. At first, I was trying to find the right setting to get the Timer to trigger a DMA request upon UEV generation. However, I could not find such a feature. So instead, I setup DMA1 Channel 3. TIM6 should map to this DMA. Then I setup TIM6 to generate a UEV upon Overflow (URS = 1, UDIS = 0). Finally, I setup TIM6 to generate a DMA request upon update (UDE = 1).

Still nothing. 

Can I get some input? 

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What I am trying to do may not be possible in the way that I thought. 

Would the DMA rapid fire send N-bytes to the SPI upon the first successful DMA request? Is there a way to get it to send only 1 byte at a time, triggered by the timer? 

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And auto-increment through memory? So..

• Timer6 -> Overflow -> UEV -> DMA -> Byte 0 -> SPI
• Timer6 -> Overflow -> UEV -> DMA -> Byte 1 -> SPI
• Timer6 -> Overflow -> UEV -> DMA -> Byte 2 -> SPI
• ...
• Timer6 -> Overflow -> UEV -> DMA -> Byte N -> SPI

[Dude]

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[Dude]

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[waclawek.jan]

Which STM32?

How do you trigger DMA? Show the register which selects the trigger source.

JW

JW

[Sarra.S · Accepted solution]

Hello @Dude, thank you for your post, 

The problem could be related to the time trigger or the DMA config as well as the SPI peripheral! 

So, first, make sure -by looking at the datasheet- that the DMA  request is lined to the right SPI peripheral 

Regarding your question about the DMA; ofc it is possible -in the DMA config- by setting the DMA transfer size to 1 byte and enabling auto-increment for the DMA source address.

Regarding the timer trigger, I think one way to know if the UEV is triggered is the use an interrupt handler for the timer's UEV and use a GPIO pin or print a message... to see if the UEV is even triggered! -Maybe it's not the easiest way but  you need to localize exactly where comes the problem

Hope that helps! 

[Dude]

Okay so the Timer is triggering an UEV event when I use interrupts. 

[Dude]

So Channel 3 should be able to be triggered by TIM 6 and cause SPI1 TX to transmit...? 

[Dude]

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[Dude]

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[Dude]

@Sarra.S 

   Are you sure that the transfers can do as I want? Thanks to you and Waclawek.jan, I am able to get the DMA to trigger, as caused by TIM6 UEV occurrence.

Will the DMA in circular buffer mode with N-bytes (CNDTR3 = N-bytes arbitrary number) move one byte per DMA request or N-bytes per DMA request? 

thanks