RE: PWM - Demo 1 Event Handler

awneil — Thu, 11 Oct 2018 08:46:38 GMT

You have read the description, and watched what the demo does, haven't you?

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.sdk5.v15.0.0%2Fpwm_hw_example.html

On an nRF52DK (PCA10040), with four LEDs, it fades each one up and then down in turn:

Fade LED1 up, then down
Fade LED2 up, then down
Fade LED3 up, then down
Fade LED4 up, then down
repeat from 1.

I do agree that Nordic could explain this much better, but the easiest way to understand this type of thing is to follow what happens in the debugger.

The first thing to note is what the m_demo1_phase variable does:

static uint8_t                     m_demo1_phase;           // 0: Fading up   LED 1
                                                            // 1: Fading down LED 1

                                                            // 2: Fading up   LED 2
                                                            // 3: Fading down LED 2
                                                            
                                                            // 4: Fading up   LED 3
                                                            // 5: Fading down LED 3
                                                            
                                                            // 6: Fading up   LED 4
                                                            // 7: Fading down LED 4

                                                            // So: Evens are fading Up;
                                                            //     Odds  are fading Down.

Which then explains what's happening here

uint8_t channel    = m_demo1_phase >> 1;
bool    down       = m_demo1_phase & 1;

The rest is just incrementing up to max during the fade-up, and then decrementing down to min for the fade down.

When the decrement reaches minimum, the next channel (ie, the next LED) is selected.