easyDMA does not support Timer in nRF52840?

[OldXiao]

Just to confirm the head question.

I have found the same question :NRF52 help configuring TIMER + DMA + PWM - Nordic Q&A - Nordic DevZone - Nordic DevZone

There is no answer at last.

I have looked through the datasheet of nRF52840, I did not find the relationship between timer & DMA.

And for PWM peripheral, it is obviously designed for control LED display,we can't change the interval of PWM output with frequency freezed,what we can changed is PWM frequency.

For IR communication with Pulse Width Modulation,we need to fix the frequency,and change the interval of PWM continue ouput. Peripheral PWM is not for IR communication,it is too waste even if you find the way to use it.

I will try to find an alter way to realize it if DMA does do not support timer.

[Håkon Alseth]

Hi,

 

For the PWM module, there are a couple of examples available here, which shows how to send patterns based on EasyDMA structs:

https://github.com/zephyrproject-rtos/hal_nordic/tree/master/nrfx/samples/src/nrfx_pwm

Or you can use the zephyr PWM api, which just sets period_A and period_B:

https://github.com/nrfconnect/sdk-zephyr/blob/main/samples/basic/blinky_pwm/src/main.c#L61

 

I did not find the relationship between timer & DMA.

There is a description in the datasheet, where table 1 shows what registers and how the hardware samples a change to those registers:

https://docs.nordicsemi.com/bundle/ps_nrf52840/page/pwm.html#ariaid-title3

 

I will try to find an alter way to realize it if DMA does do not support timer.

You can use GPIOTE + PPI + TIMER instance to generate a simple PWM output, but this will require manual intervention on each update.

 

Kind regards,

Håkon

[OldXiao]

Thank you for your reply.

I am using nRF52 SDK, so ignore zephyr.

DMA dose not support timer directly, I nee to change CC of timer on fly,the interrupt handler will be adopted without direct support from DMA. and the limitation of interrupt handler is it will be interrupted if higher priority event comes,RADIO events for example.

I have figured a way to finish it without CPU involvement.

Close this ticket ,please.