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.. currentmodule:: machine
.. _machine.TimerWiPy:
class TimerWiPy -- control hardware timers
==========================================
.. note::
This class is a non-standard Timer implementation for the WiPy.
It is available simply as ``machine.Timer`` on the WiPy but is named in the
documentation below as ``machine.TimerWiPy`` to distinguish it from the
more general :ref:`machine.Timer <machine.Timer>` class.
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
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.
Constructors
------------
.. class:: TimerWiPy(id, ...)
Construct a new timer object of the given id. Id of -1 constructs a
virtual timer (if supported by a board).
Methods
-------
.. method:: TimerWiPy.init(mode, *, width=16)
Initialise the timer. Example::
tim.init(Timer.PERIODIC) # periodic 16-bit timer
tim.init(Timer.ONE_SHOT, width=32) # one shot 32-bit timer
Keyword arguments:
- ``mode`` can be one of:
- ``TimerWiPy.ONE_SHOT`` - The timer runs once until the configured
period of the channel expires.
- ``TimerWiPy.PERIODIC`` - The timer runs periodically at the configured
frequency of the channel.
- ``TimerWiPy.PWM`` - Output a PWM signal on a pin.
- ``width`` must be either 16 or 32 (bits). For really low frequencies < 5Hz
(or large periods), 32-bit timers should be used. 32-bit mode is only available
for ``ONE_SHOT`` AND ``PERIODIC`` modes.
.. method:: TimerWiPy.deinit()
Deinitialises the timer. Stops the timer, and disables the timer peripheral.
.. method:: TimerWiPy.channel(channel, **, freq, period, polarity=TimerWiPy.POSITIVE, duty_cycle=0)
If only a channel identifier passed, then a previously initialized channel
object is returned (or ``None`` if there is no previous channel).
Otherwise, a TimerChannel object is initialized and returned.
The operating mode is the one configured to the Timer object that was used to
create the channel.
- ``channel`` if the width of the timer is 16-bit, then must be either ``TIMER.A``, ``TIMER.B``.
If the width is 32-bit then it **must be** ``TIMER.A | TIMER.B``.
Keyword only arguments:
- ``freq`` sets the frequency in Hz.
- ``period`` sets the period in microseconds.
.. note::
Either ``freq`` or ``period`` must be given, never both.
- ``polarity`` this is applicable for ``PWM``, and defines the polarity of the duty cycle
- ``duty_cycle`` only applicable to ``PWM``. It's a percentage (0.00-100.00). Since the WiPy
doesn't support floating point numbers the duty cycle must be specified in the range 0-10000,
where 10000 would represent 100.00, 5050 represents 50.50, and so on.
.. note::
When the channel is in PWM mode, the corresponding pin is assigned automatically, therefore
there's no need to assign the alternate function of the pin via the ``Pin`` class. The pins which
support PWM functionality are the following:
- ``GP24`` on Timer 0 channel A.
- ``GP25`` on Timer 1 channel A.
- ``GP9`` on Timer 2 channel B.
- ``GP10`` on Timer 3 channel A.
- ``GP11`` on Timer 3 channel B.
class TimerChannel --- setup a channel for a timer
==================================================
Timer channels are used to generate/capture a signal using a timer.
TimerChannel objects are created using the Timer.channel() method.
Methods
-------
.. method:: timerchannel.irq(*, trigger, priority=1, handler=None)
The behaviour of this callback is heavily dependent on the operating
mode of the timer channel:
- If mode is ``TimerWiPy.PERIODIC`` the callback is executed periodically
with the configured frequency or period.
- If mode is ``TimerWiPy.ONE_SHOT`` the callback is executed once when
the configured timer expires.
- If mode is ``TimerWiPy.PWM`` the callback is executed when reaching the duty
cycle value.
The accepted params are:
- ``priority`` level of the interrupt. Can take values in the range 1-7.
Higher values represent higher priorities.
- ``handler`` is an optional function to be called when the interrupt is triggered.
- ``trigger`` must be ``TimerWiPy.TIMEOUT`` when the operating mode is either ``TimerWiPy.PERIODIC`` or
``TimerWiPy.ONE_SHOT``. In the case that mode is ``TimerWiPy.PWM`` then trigger must be equal to
``TimerWiPy.MATCH``.
Returns a callback object.
.. method:: timerchannel.freq([value])
Get or set the timer channel frequency (in Hz).
.. method:: timerchannel.period([value])
Get or set the timer channel period (in microseconds).
.. method:: timerchannel.duty_cycle([value])
Get or set the duty cycle of the PWM signal. It's a percentage (0.00-100.00). Since the WiPy
doesn't support floating point numbers the duty cycle must be specified in the range 0-10000,
where 10000 would represent 100.00, 5050 represents 50.50, and so on.
Constants
---------
.. data:: TimerWiPy.ONE_SHOT
.. data:: TimerWiPy.PERIODIC
Timer operating mode.
|
