PWM options when using FreeRTOS and SoftDevice

[Tim Adu]

Hi,

I'm developing a BLE application that is also using FreeRTOS.

I also need to use PWM to control an LED (mainly because the requirements define LED patterns, which is best accomplished using PWM; otherwise I would just use the FreeRTOS timer).

I can see 3 PWM libraries:

• PWM driver
• Low power PWM
• Softblink library

Which one of these is best to use with a FreeRTOS + SoftDevice application?

Thanks

Tim

[Susheel Nuguru]

Hi Adu,

Softblink is a simple library mainly used for LED softblink application and it internally uses low power PWM. 

APP PWM uses PPI/GPIOTE and few other resources to abstract more functionality to the app.

For your use case using low power pwm seems to fit fine even though you are using FreeRTOS. Just remember that you need to include app_timer_freertos.c instead of app_timer.c in your  project as low power pwm library uses app_timer.

[Tim Adu]

Thank you Susheel,

I got it to work. One last question: how would you go about implementing a LED fade in/out pattern?
The LED softblink library made it easy by having a duty_cycle_step parameter. Is there a way to do it with the Low power PWM?

[Susheel Nuguru]

Sorry for the late reply, just came back from the holidays.

The low power PWM does have automated change of duty cycle like softblink. App needs to wakeup in timer callbacks and do the change using low_power_pwm_duty_set

[Aurele]

Hello,

Is it advised to use low power PWM with FreeRTOS ? I'm asking because i know this is a software pwm and it is using app_timer that is using xTimerTask. All FreeRTOS timer handler are called from a task context. Isn't it more appropriate to use a custom hardware timer for low power pwm ?

Regards,

Aurélien

[Susheel Nuguru]

 Aurélien,

Aurele said:

Isn't it more appropriate to use a custom hardware timer for low power pwm ?

To achieve proper low power and accurate PWM it would be appropriate to use a custom hardware timer. For some this choice is not an option due to cost/complexity reasons.