lib: Make sure that PWM continues to work even if it misses an IRQ. #607
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If the soft PWM driver misses an IRQ then the next CC value (computed as
CC[x] += delay) could already be behind the timer counter value, and hence
the next compare IRQ won't fire until the timer counter value wraps around.
Example code which demonstrates the bug (by having a long neopixel write
that stops IRQs):
import microbit
import music
import neopixel
np = neopixel.NeoPixel(microbit.pin0, 64)
while True:
music.play(music.BA_DING, wait=False)
microbit.sleep(1000)
np.clear()
microbit.sleep(2000)
Prior to this commit the music would only play every 16 seconds or so,
which is the time taken for the PWM fast ticker to wrap around.
Fixes issue bbcmicrobit#600.
Signed-off-by: Damien George <damien@micropython.org>
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This fix was updated so that it retained precise PWM timing in the case when no IRQs were missed. |
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If the soft PWM driver misses an IRQ then the next CC value (computed as CC[x] += delay) could already be behind the timer counter value, and hence the next compare IRQ won't fire until the timer counter value wraps around.
This needs some testing because the timing of the PWM will now be slightly different compared to before, since the next event will be computed from the current counter value plus delay, rather than the counter value at the time of the previous IRQ. But I can't really think of any other way to fix the issue of missed IRQs.
Should fix #600