Using PWM peripheral to output fixed number of pulses

RE: Using PWM peripheral to output fixed number of pulses

Sigurd — Mon, 24 Apr 2023 08:43:57 GMT

Hi,

I don't know how this stepper motor signal looks like, but maybe it's possible for you to use the QDEC to keep track of that https://infocenter.nordicsemi.com/topic/ps_nrf52840/qdec.html?cp=5_0_0_5_17

RE: Using PWM peripheral to output fixed number of pulses

jcondon — Fri, 21 Apr 2023 14:18:00 GMT

This is unfortunate and precludes the use of the PWM for stepper motors. If you ever wanted the motor command to stop, change direction, or change the end position of the motor while a sequence is running, you would lose the step count and have to re-home the motor.

The only way I can see to accomplish this is using the EVENTS_PWMPERIODEND event and tie it to a Timer's TASKS_COUNT. However, we don't have enough timer peripherals left for our application.

We'll have to move to a different processor line.

RE: Using PWM peripheral to output fixed number of pulses

Sigurd — Fri, 21 Apr 2023 08:28:17 GMT

Hi,

[quote user="jcondon"]Is there a way to read what the current count/repeats (i.e. how many pulses) the PWM has sent out while it's operating. Similarly is there a way to read out the number of pulses sent after STOP is issued?[/quote]

Looking at the PWM chapter in the Product Specification, the PWM peripheral does not support this. You set the number of pulses you want to send, and you get an event when that have completed.

Maybe you could use a logic analyzer, and check that your FW implementation matches what you are trying to do with the logic analyzer.

RE: Using PWM peripheral to output fixed number of pulses

jcondon — Thu, 20 Apr 2023 18:57:41 GMT

Nordic's drivers are not written in a way that lends themself to our framework. We typically use the nrfx drivers as reference and adapt them to our purposes. However, let's pretend I'm using them...

Is there a way to read what the current count/repeats (i.e. how many pulses) the PWM has sent out while it's operating. Similarly is there a way to read out the number of pulses sent after STOP is issued?

RE: Using PWM peripheral to output fixed number of pulses

Sigurd — Thu, 20 Apr 2023 08:57:53 GMT

Hi,

[quote user=""]Note: Settings are being controlled directly through register writes[/quote]

As a general note, I recommend using our drivers.

You can see how your use-case is handled by the nrfx_pwm_simple_playback() function.

https://github.com/NordicSemiconductor/nrfx/blob/master/drivers/src/nrfx_pwm.c#L294

I.e. set the loop register , and set the SHORT between LOOPSDONE and STOP