STM32L0 -> DMA, parallel operations

[Dude]

Dumb question,

can the DMA perform separate, parallel operations with the different channels? For example, could I use the DMA to transmit with the UART and the SPI devices at the same time without one interrupting the other? I'm unclear from reading through the DMA datasheet whether its possible to have parallel operations or whether the DMA controller only lines up and allows one at a time.

Provided those operations don't conflict by needing to access the same resources, of course.

[RBENF.1 · Accepted solution]

Hello @Dude​,

When using a single DMA controller with multiple channels, an arbitration is performed for AHB bus access.

To achieve parallel operation, you would need to use two different DMA controllers, as long as they are not conflicting within the bus matrix. You can refer to AN2548 for detailed information.

Regards,

Ryan

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[Danish1]

There’s a subtlety to your question:

When you say parallel, do you mean at precisely the same time (down to the same processor clock-tick) or are you just after both DMA channels to run seemingly at the same time, bus accesses for each as-and-when their peripherals are ready (where the occasional singe-processor-cycle delay due to bus contention is not a problem).

if the latter, you just need different channels; they can be on the same DMA controller. You don’t need to do anything special - just set one running then set the other running.

[Dude]

You are right, due to the speed of the DMA controller I don't need precisely at the same time. Simply being able to request multiple transfers on different channels is sufficient. 

Also, I got this working but forgot to follow up. thanks.