circuitpython/docs/library/machine.Timer.rst

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.. currentmodule:: machine
.. _machine.Timer:
class Timer -- control hardware timers
======================================
Hardware timers deal with timing of periods and events. Timers are perhaps
the most flexible and heterogeneous kind of hardware in MCUs and SoCs,
differently greatly from a model to a model. MicroPython's Timer class
defines a baseline operation of executing a callback with a given period
(or once after some delay), and allow specific boards to define more
2021-04-30 02:53:36 -04:00
non-standard behaviour (which thus won't be portable to other boards).
See discussion of :ref:`important constraints <machine_callbacks>` on
Timer callbacks.
.. note::
Memory can't be allocated inside irq handlers (an interrupt) and so
exceptions raised within a handler don't give much information. See
:func:`micropython.alloc_emergency_exception_buf` for how to get around this
limitation.
If you are using a WiPy board please refer to :ref:`machine.TimerWiPy <machine.TimerWiPy>`
instead of this class.
Constructors
------------
.. class:: Timer(id, /, ...)
Construct a new timer object of the given ``id``. ``id`` of -1 constructs a
virtual timer (if supported by a board).
``id`` shall not be passed as a keyword argument.
See ``init`` for parameters of initialisation.
Methods
-------
.. method:: Timer.init(*, mode=Timer.PERIODIC, freq=-1, period=-1, callback=None)
Initialise the timer. Example::
def mycallback(t):
pass
# periodic at 1kHz
tim.init(mode=Timer.PERIODIC, freq=1000, callback=mycallback)
# periodic with 100ms period
tim.init(period=100, callback=mycallback)
# one shot firing after 1000ms
tim.init(mode=Timer.ONE_SHOT, period=1000, callback=mycallback)
Keyword arguments:
- ``mode`` can be one of:
- ``Timer.ONE_SHOT`` - The timer runs once until the configured
period of the channel expires.
- ``Timer.PERIODIC`` - The timer runs periodically at the configured
frequency of the channel.
- ``freq`` - The timer frequency, in units of Hz. The upper bound of
the frequency is dependent on the port. When both the ``freq`` and
``period`` arguments are given, ``freq`` has a higher priority and
``period`` is ignored.
- ``period`` - The timer period, in milliseconds.
- ``callback`` - The callable to call upon expiration of the timer period.
The callback must take one argument, which is passed the Timer object.
The ``callback`` argument shall be specified. Otherwise an exception
will occur upon timer expiration:
``TypeError: 'NoneType' object isn't callable``
.. method:: Timer.deinit()
Deinitialises the timer. Stops the timer, and disables the timer peripheral.
Constants
---------
.. data:: Timer.ONE_SHOT
Timer.PERIODIC
Timer operating mode.