Commit dab0f316 authored by Peter Hinch's avatar Peter Hinch Committed by Damien George
Browse files

docs/reference/isr_rules.rst: Two minor additions to docs for using ISR.

- Refers to the technique of instantiating an object for use in an ISR by
  specifying it as a default argument.

- Footnote detailing the fact that interrupt handlers continue to be
  executed at the REPL.
parent 742d8bdb
......@@ -110,6 +110,19 @@ the flag. The memory allocation occurs in the main program code when the object
The MicroPython library I/O methods usually provide an option to use a pre-allocated buffer. For
example ``pyb.i2c.recv()`` can accept a mutable buffer as its first argument: this enables its use in an ISR.
A means of creating an object without employing a class or globals is as follows:
.. code:: python
def set_volume(t, buf=bytearray(3)):
buf[0] = 0xa5
buf[1] = t >> 4
buf[2] = 0x5a
return buf
The compiler instantiates the default ``buf`` argument when the function is
loaded for the first time (usually when the module it's in is imported).
Use of Python objects
~~~~~~~~~~~~~~~~~~~~~
......@@ -300,3 +313,20 @@ that access to the critical variables is denied. A simple example of a mutex may
but only for the duration of eight machine instructions: the benefit of this approach is that other interrupts are
virtually unaffected.
Interrupts and the REPL
~~~~~~~~~~~~~~~~~~~~~~~
Interrupt handlers, such as those associated with timers, can continue to run
after a program terminates. This may produce unexpected results where you might
have expected the object raising the callback to have gone out of scope. For
example on the Pyboard:
.. code:: python
def bar():
foo = pyb.Timer(2, freq=4, callback=lambda t: print('.', end=''))
bar()
This continues to run until the timer is explicitly disabled or the board is
reset with ``ctrl D``.
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