PWM Driver - Proper Way to Update Sequence

RE: PWM Driver - Proper Way to Update Sequence

ovrebekk — Fri, 04 May 2018 13:37:52 GMT

Thanks for the project, I see the same issue here.

The behavior seems to be caused by two factors:

a) The end_delay is added between each playback of the sequence, not after the sequence has looped X number of times.

b) On the last loop the end_delay is not added, so that the sequence is played back twice in succession.

This behavior is more obvious if you increase the loop count to 3.

I will check with the SDK guys next week if this is expected behavior, or if there is some bug in the driver.

As a temporary workaround I would suggest the following: Set the end_delay to 0, and use the loop value to determine how many times the sequence should loop before the delay.

Use an app_timer (or a dedicated RTC timer) to control the delay between sequence loops, rather than the end_delay factor. The simplest way to do this is to call nrf_drv_pwm_simple_playback(..) directly from the app_timer callback.

Best regards
Torbjørn

RE: PWM Driver - Proper Way to Update Sequence

amorgan — Fri, 27 Apr 2018 14:32:09 GMT

ovrebekk, thanks for the example code. I have modified your example to reproduce the error that I am seeing in my code.

I set Channels 1 - 3 to NRF_DRV_PWM_PIN_NOT_USED. And modified the sequence to match what I am trying to achieve. I do want the flashing sequence to loop because I would like for this to loop until the state is changed (this will act as a warning sequence).

The issue I am seeing is that after pressing button 2, to start the "static" sequence, that is just one value, then pressing button 1 to start the "flashing" sequence, even though the playback is set to 2, on the very first playback, it only plays it once, delays, then every sequence after that, it does playback twice, then loops.

More succinctly :

1) Press Button 2

2) LED 1 is on static

3) Press Button 1

4) LED 1 turns off, turns on (not expected)

5) LED 1 sequence delays

6) LED 1 turns off, turns on, turns off, turns on (exprected)

7) LED 1 sequence delays

8) Sequence continues to loop

Step 4 is what is not expected. I expect it to behave like step 6 immediately.

Thank you,

/cfs-file/__key/communityserver-discussions-components-files/4/8780.pwm_5F00_driver_5F00_sequence_5F00_static_5F00_modified.zip

RE: PWM Driver - Proper Way to Update Sequence

ovrebekk — Fri, 27 Apr 2018 07:36:07 GMT

Just to be clear, some times you need to set the PWM to a static value, and other times you want to play a sequence?

I modified the standard SDK example to do something similar, and you will find it attached. Pressing button 1 will start a sequence, and pressing button 2 will set the 4 LED's to static values.

Exactly what is wrong with your example I am not sure. If you are trying to play a sequence I would use NRF_DRV_PWM_FLAG_STOP rather than NRF_DRV_PWM_FLAG_LOOP. Otherwise there is nothing in your code that jumps out at me.

Best regards
Torbjørn