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