[Bug Report] coin_toss triggering on falling slope instead of rise

[Tyler Schreiber]

Bug Report

Describe the bug
When in external clock mode, coin_toss is triggered on the falling slope, rather than the rise

To Reproduce
Steps to reproduce the behavior:

1. Run coin_toss.py
2. Set it to external clock mode
3. Feed it a 50% duty square wave as a clock
4. The tosses are triggered on the falling slope rather than the rise

Expected behavior
It's expected that the tosses would be triggered when the rising slope is first detected

Solution
The problem appears to be here:

def wait(self):
        """Pause script execution waiting for next quarter note in the clock cycle."""
        if self.internal_clock:
            while True:
                if ticks_diff(self._deadline, ticks_ms()) <= 0:
                    self._deadline = self.get_next_deadline()
                    return
        else:  # External clock
            # Loop until digital in goes high (clock pulse received).
            while not self.internal_clock:
                if din.value() != self._prev_clock:
                    # We've detected a new clock value.
                    self._prev_clock = 1 if self._prev_clock == 0 else 0
                    # If the previous value is 0 then we are seeing a high 
                    # value for the first time, break wait and return.
                    if self._prev_clock == 0:
                        return

The second to last line should be if self._prev_clock == 1: since the self._prev_clock value was just changed.

[Tyler Schreiber]

This may or may not be unexpected behavior - but triggering on the falling part of the pulse seems unusual.

[Adam Wonak]

Thanks for catching this and for the detailed bug fix tips! Yeah, this script was one of the first scripts written and came in before we added the rising and falling handlers, which would handle this much better: https://allen-synthesis.github.io/EuroPi/generated/europi.html#europi.DigitalInput

If you like this script, there's an even better version in the works written by @Bridgee in PR #104. Stay tuned for that one!

In the mean time, feel free to submit a pull request if you've got a fix, or I can work on it in the following days.

[Tyler Schreiber]

Oh, very cool! I'm looking forward to that one. The EuroPi is such a great project.

I'm on my phone right now, but can probably get a PR together tonight or tomorrow with the fix.