RTC wakeup callback should be executed immediately rather than deferred
AFAIK the callback invoked by RTC.wakeup is scheduled for later execution rather than being executed immediately, as the pin interrupts are.
See: https://github.com/micropython/micropython/blob/master/ports/stm32/extint.c#L657
IMHO this is undesirable behaviour. If the RTC is used to (a) wake the processor after machine.sleep() and (b) set a flag to be inspected by the main thread, then it has the effect that the flag may not be ready for inspection.
The code below illustrated the problem. I find that for correct operation it is necessary to add a delay after execution resumes and before inspecting variables changed by the callback. Commenting out the delay at line 17 results in undesirable behaviour.
I ran this on an OpenMV camera and the OpenMV github issue here provides more details of how I found this bug/feature, and some further analysis https://github.com/openmv/openmv/issues/1032
`
import machine, pyb, time
global triggered
triggered = False
def callback(arg):
global triggered
triggered = True
pyb.RTC().wakeup(1000, callback)
while (True):
machine.sleep()
# At this point the RTC will have woken us but the callback may not have been executed.
# This delay is essential to allow the callback to execute and update 'triggered'
time.sleep_ms(1) # Required minimum delay is not known. Do not use sleep_us()
if (triggered):
# Toggle green LED to indicate correct behaviour.
# 'triggered' is seen as having changed
pyb.LED(2).toggle()
else:
# Toggle red LED to indicate incorrect behaviour.
# 'triggered' is NOT seen as having changed
pyb.LED(1).toggle()
triggered = False
`
stm32: Fix passing invalid argument to RTC callback.
Summary
The folling code does not work with NUCLEO_F401RE.
from pyb import RTC
def cb(v):
print(v)
rtc=RTC()
rtc.wakeup(1000, cb)
NameError exception occurred with following message.
The argument of callback should be accessed without exception.
Traceback (most recent call last):
File "<stdin>", line 2, in cb
NameError: local variable referenced before assignment
To fix this issue, this PR passes EXTI_RTC_WAKEUP to callback argument.
This is equivalent behavior with ExtInt callback when ExtInt is mapped to RTC interrupt by passing an integer value.
Testing
Tested with NUCLEO_F401RE.
The argument of callback can be read (22 with NUCLEO_F401RE).