Tiva C - uDMA serve PWM duty - possible?

Simon Wolf

Other Parts Discussed in Thread: TM4C123GH6PM

Hi,

I'm actually doing my very first signal processing with the TM4C123GH6PM on the Tiva C Launchpad.

In my mind, I'm sampling some data by using ADC0 and uDMA in ping-pong mode. Do some kind of filtering and write the data into the output ping/pong buffer. Out of this buffer another uDMA channel will update the COMP value of any PWM generator.

The ADC will be triggered by the PWM counter - therefore the system runs synchronous.

My problem is how to write to PWMnCMPA register using DMA in circular mode? I know there is no hardware channel providing this, but using a software channel could be possible?!

Thanks for any impressions!

Simon

over 9 years ago

0 Amit Ashara over 9 years ago

TI__Guru**** 244440 points

Hello Simon,

When with the "DMA" do the write to the PWMnCMPA? The periodicity of the same is not specified, every PWM cycle, every X seconds or on certain conditions like value exceeding or below a threshold or a signal?

0 Simon Wolf over 9 years ago in reply to Amit Ashara

Prodigy 105 points

If the PWM counter triggers the ADC, I have to update PWMnCMPA every PWM cycle. Otherwise I got output sampling rate lower than input rate.

0 Amit Ashara over 9 years ago in reply to Simon Wolf

TI__Guru**** 244440 points

Hello Simon,

Then why use the DMA at all. It would be much simpler to use the CPU. The CPU updates the value for the PWMnCMPA and the value is loaded by the PWM on the next timeout based on the update mechanism configured in the PWM module.

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Tiva C - uDMA serve PWM duty - possible?