CODEWITHSUNDEEP
raspberry-piwindows-10-iot-core
Slicc
Slicc

Reputation: 3445

raspberry pi lightning dma pwm flickery

I'm using the lightning drivers with windows IoT core to drive a PWM output. I've attached a scope to the GPIO pin and I set the PWM duty cycle. I do this in an infinite loop. If I put a delay in the loop then the output signal looks fine. If I drop the delay however, the duty cycle (as seen on the scope) starts to flicker between 5 and 10%. Code below, can anyone explain this?

        var controllers = await PwmController.GetControllersAsync(LightningPwmProvider.GetPwmProvider());
        var pwmController = controllers[1];
        pwmController.SetDesiredFrequency(50);

        var motor1 = pwmController.OpenPin(5);
        motor1.Start();

        do
        {
            motor1.SetActiveDutyCyclePercentage(0.05);
            Task.Delay(1000).Wait();
        } while (true);

Upvotes: 1

Views: 338

Answers (1)

Haukman
Haukman

Reputation: 3776

I'm just guessing here, but could it be that SetActiveDutyCyclePercentage will actually reset the PWM counter, so it'll mess up the current cycle in the PWM. If you do it repeatedly then it'll mess up a lot of the cycles, vs. putting in a delay. Think about PWM as a counter that flips the output when it hits 0. If you reset the counter (with the SetActiveDutyCyclePercentage call) then the current cycle's total number of counts = length (before it flips the output) will be skewed.

Upvotes: 0

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