Suggested tests for Pico PWM

[tdunning]

This is an enhancement suggestion.

For testing the PWM on the Pico, I would suggest

1. connecting PWM2 output to a GPIO and PWM3 input
2. connecting PWM0 output to PWM1 input
3. connecting PWM3 output to PWM0 input

This would allow testing of:

1. PWM free running generation of signals (generate using PWM2, poll the GPIO)
2. PWM counting external signal (use PWM2 in free running mode, poll GPIO, observe counts on PWM3)
3. PWM generation of output signal (see test (1) and (2))
4. PWM generation of an interrupt at the right time and for correct edge (feed PWM1 a signal from PWM0, generate interrupts from GPIO and PWM1 rollover. interrupt handlers should read time and write to a channel)
5. DMA and PIO integration with PWM (use PWM2 as a pulse-per-second emulator, PWM3 to generate high frequency in and run the go-wspr frequency counter)