c8b7628094
Makes sure that classes described in these separate files are properly designated as belonging to "machine" module in indexes.
217 lines
8.4 KiB
ReStructuredText
217 lines
8.4 KiB
ReStructuredText
.. currentmodule:: machine
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.. _machine.Timer:
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class Timer -- control internal timers
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======================================
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.. only:: port_wipy
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Timers can be used for a great variety of tasks, calling a function periodically,
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counting events, and generating a PWM signal are among the most common use cases.
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Each timer consists of two 16-bit channels and this channels can be tied together to
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form one 32-bit timer. The operating mode needs to be configured per timer, but then
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the period (or the frequency) can be independently configured on each channel.
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By using the callback method, the timer event can call a Python function.
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Example usage to toggle an LED at a fixed frequency::
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from machine import Timer
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from machine import Pin
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led = Pin('GP16', mode=Pin.OUT) # enable GP16 as output to drive the LED
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tim = Timer(3) # create a timer object using timer 3
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tim.init(mode=Timer.PERIODIC) # initialize it in periodic mode
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tim_ch = tim.channel(Timer.A, freq=5) # configure channel A at a frequency of 5Hz
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tim_ch.irq(handler=lambda t:led.toggle(), trigger=Timer.TIMEOUT) # toggle a LED on every cycle of the timer
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Example using named function for the callback::
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from machine import Timer
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from machine import Pin
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tim = Timer(1, mode=Timer.PERIODIC, width=32)
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tim_a = tim.channel(Timer.A | Timer.B, freq=1) # 1 Hz frequency requires a 32 bit timer
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led = Pin('GP16', mode=Pin.OUT) # enable GP16 as output to drive the LED
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def tick(timer): # we will receive the timer object when being called
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global led
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led.toggle() # toggle the LED
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tim_a.irq(handler=tick, trigger=Timer.TIMEOUT) # create the interrupt
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Further examples::
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from machine import Timer
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tim1 = Timer(1, mode=Timer.ONE_SHOT) # initialize it in one shot mode
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tim2 = Timer(2, mode=Timer.PWM) # initialize it in PWM mode
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tim1_ch = tim1.channel(Timer.A, freq=10, polarity=Timer.POSITIVE) # start the event counter with a frequency of 10Hz and triggered by positive edges
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tim2_ch = tim2.channel(Timer.B, freq=10000, duty_cycle=5000) # start the PWM on channel B with a 50% duty cycle
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tim2_ch.freq(20) # set the frequency (can also get)
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tim2_ch.duty_cycle(3010) # set the duty cycle to 30.1% (can also get)
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tim2_ch.duty_cycle(3020, Timer.NEGATIVE) # set the duty cycle to 30.2% and change the polarity to negative
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tim2_ch.period(2000000) # change the period to 2 seconds
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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:: machine.Timer(id, ...)
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.. only:: port_wipy
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Construct a new timer object of the given id. ``id`` can take values from 0 to 3.
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Methods
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-------
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.. only:: port_wipy
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.. method:: timer.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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- ``Timer.ONE_SHOT`` - The timer runs once until the configured
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period of the channel expires.
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- ``Timer.PERIODIC`` - The timer runs periodically at the configured
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frequency of the channel.
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- ``Timer.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:: timer.deinit()
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Deinitialises the timer. Disables all channels and associated IRQs.
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Stops the timer, and disables the timer peripheral.
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.. only:: port_wipy
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.. method:: timer.channel(channel, \**, freq, period, polarity=Timer.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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Othwerwise, 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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.. only:: port_wipy
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.. method:: timerchannel.irq(\*, trigger, priority=1, handler=None)
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The behavior of this callback is heaviliy dependent on the operating
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mode of the timer channel:
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- If mode is ``Timer.PERIODIC`` the callback is executed periodically
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with the configured frequency or period.
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- If mode is ``Timer.ONE_SHOT`` the callback is executed once when
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the configured timer expires.
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- If mode is ``Timer.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 ``Timer.TIMEOUT`` when the operating mode is either ``Timer.PERIODIC`` or
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``Timer.ONE_SHOT``. In the case that mode is ``Timer.PWM`` then trigger must be equal to
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``Timer.MATCH``.
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Returns a callback object.
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.. only:: port_wipy
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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:: Timer.ONE_SHOT
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.. data:: Timer.PERIODIC
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.. data:: Timer.PWM
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Selects the timer operating mode.
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.. data:: Timer.A
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.. data:: Timer.B
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Selects the timer channel. Must be ORed (``Timer.A`` | ``Timer.B``) when
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using a 32-bit timer.
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.. data:: Timer.POSITIVE
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.. data:: Timer.NEGATIVE
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Timer channel polarity selection (only relevant in PWM mode).
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.. data:: Timer.TIMEOUT
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.. data:: Timer.MATCH
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Timer channel IRQ triggers.
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