extmod/uasyncio: Add clear method to ThreadSafeFlag.

This is useful in situations where the ThreadSafeFlag is reused and needs
to be cleared of any previous, unwanted event.

For example, clear the flag at the start of an operation, trigger the
operation (eg an I2C write), then (a)wait for an external event to set the
flag (eg a pin IRQ).  Further events may trigger the flag again but these
are unwanted and should be cleared before the next cycle starts.

1 files changed, 4 insertions, 1 deletions

diff --git a/extmod/uasyncio/event.py b/extmod/uasyncio/event.py
index c48904b98..654ccefa9 100644
--- a/extmod/uasyncio/event.py
+++ b/extmod/uasyncio/event.py
@@ -36,7 +36,7 @@ class Event:
 # MicroPython-extension: This can be set from outside the asyncio event loop,
 # such as other threads, IRQs or scheduler context. Implementation is a stream
 # that asyncio will poll until a flag is set.
-# Note: Unlike Event, this is self-clearing.
+# Note: Unlike Event, this is self-clearing after a wait().
 try:
     import uio
 
@@ -52,6 +52,9 @@ try:
         def set(self):
             self._flag = 1
 
+        def clear(self):
+            self._flag = 0
+
         async def wait(self):
             if not self._flag:
                 yield core._io_queue.queue_read(self)