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import board, digitalio
class WithTest:
def __init__(self):
pass
def __enter__(self):
pass
def __exit__(self, *exc):
pass
d13 = digitalio.DigitalInOut(board.D13)
d13.switch_to_output()
# CYCLICALLY INCREASING INTERVALS
wt = WithTest()
while True:
with wt as wtx:
d13.value = not d13.value
#OK: CONSTANT INTERVALS
while True:
with WithTest() as wt:
d13.value = not d13.valuePutting a scope on D13 will show a square wave whose period gets longer and longer and then snaps back and starts over. On an M0 the period is increasing from very roughly 0.5 msec to 5 msec (eyeballing it on the scope).
The upper loop shows the problem. The lower loop (comment out the upper one) shows constant intervals.
This was originally discovered by @ladyada when monitoring an I2C transaction that used adafruit_bus_device.I2CDevice. But it has nothing to do with I2C.
This is easiest to see on an oscilloscope:
https://youtu.be/tGB2uVwig_4 (unlisted; use the link)
Screen shots from Saleae:
first loop (taken at gap: starts fast after a gap and slows down):
second loop (constant before and after gap):
Also filed as micropython#5622.
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