Can we implment PWM Analyzer on SDK 11?

[Ron]

I need to implement a PWM analyzer. I looked at the example in SDK 6 and it's fairly easy to follow. When I tried it, it doesn't look like GPIOTE handler gets called frequently enough. Is there a better recommendation to calculate duty cycle other than using GPIOTE that will do a good job sensing the rise and drop?

[Einar Thorsrud]

The peripherals use a 16 MHz clock, which is a limiting factor when measurements are performed using PPI. Using GPIOTE and a timer connected via PPI as the pwm_analyzer example in SDK 6 is a sensible way of doing the measurements. You can also use a comparator instead of GPIOTE.

If the frequency of the PWM signal you are analyzing is too high compared to what you are measuring with, you could consider low pass filtering the PWM signal and using the ADC. This will have a few disadvantages, though. It will require an external RC filter and will have lower accuracy.

A few questions:

• What is the maximum frequency of the PWM signal you need to analyze?
• Are you using nRF52 or nRF51?

[Einar Thorsrud]

You are right, you cannot get events for both low-to-high and high-to-low transitions on one GPIO pin using GPIOTE. What you can do is to use one pin with the comparator instead, as there you have separate events for low-to-high and high-to-low transitions. Alternatively you can use two GPIO pins. Using GPIOTE with polarity toggle can be a problem, as you cannot be certain about the polarity.

Of course if you are happy with doing parts of the measurements in software, as the example in SDK 6, this is less of an issue. However you will have less accurate measurements, particularly when higher priority interrupts occur while measuring (as discussed earlier in this thread).

There may be a smarter way of doing this that has not come to my mind. It will be interesting to see how you solve it.