Question regarding ADC and DMA tranfer.

[matic]

Posted on August 31, 2015 at 15:38

Hi.

I make 4 ADCs on ADC1 and other 4 on ADC2. I'm using DUAL mode, so the results are transferred in 32-bit word (one half for ADC1 and another half for ADC2). Thus I need 4 conversion times for all 8 conversions. The destination address for DMA is an array of 8 16-bit words and it works. Let's call this as one sequence. Now, I would like to make more than one sequence with single trigger for AD start. Let say, I would like to make 10 sequences (for 80 conversions), which would take time equal to 40 conversions (because of DUAL mode). If I am correct, I should define a destination array for DMA as 80 16-bit words and set the number of DMA tranfers to 40 (40 times of 32-bit). ADC should be configured in SCAN mode as well. But now, I am not sure how should be ''number of conversions'' configured? As I said, I have 4 channels on each ADC and each ADC should go 10 times over the same channel (for ADC1: CH0 - CH1 - CH2 - CH3 - CH0 - CH1 - CH2 - CH3 - CH0 - ... 10x like this). And same for ADC2. Would this work if I set number of conv. to 4 (for both ADCs), and DMA transfers to 40? Would ADC go throug all 40 (10x 4) conversions automatically? Thanks  #adc #dma

[Tesla DeLorean]

Posted on August 31, 2015 at 16:53

Well I'm not sure you can trigger multiple sets of samples. Basically in non-continuous mode it's going to do your 4x2 samples every time it gets a trigger.

You could try continuous mode, but problem is that it might not stop. You could try using a trigger, and experiment.

[matic]

Posted on August 31, 2015 at 17:21

Is possible to start  AD in CONTINUOUS mode by software at certain moment and then also

interrupt

(finish) AD conversions when you want? If that is possible, then I would start AD in continuous mode when I want and wait for TCIF (transfer complete) flag for DMA. This would be configured to 40 transfers. Then in ISR I would stop ADC.

[Tesla DeLorean]

Posted on August 31, 2015 at 18:33

You'd have to do what I do, experiment.

You can limit the sampling with the DMA TC, with the DMA in Normal mode. The problem that I see is getting the ADC reinitialized, because when the DMA stops servicing the ADC will over-run. Restarting it, and resynchronizing the scan, might take some effort.

[mauro2399]

Posted on September 01, 2015 at 12:35

I agree with clive1, the cleanest way is having the ADC run continuously looping on a sequence of 4 conversions, and let the DMA stop it (by overrun) when the buffer is full, then fire an IRQ and reset the DMA and ADC units.

[matic]

Posted on September 01, 2015 at 21:00I am not sure if I understand right. When all DMA transfers will be carried out, program goes to DMA IRQ_Handler (because of transfer complete interrupt enable). At that point, overrun flag should be set automatically? But why should I look for that flag at all? Is not enough that, when TCIF is set, I know the buffer is full (all conversions are done) and I just stop ADC and reset it?