216 lines
8.4 KiB
ReStructuredText
216 lines
8.4 KiB
ReStructuredText
.. currentmodule:: machine
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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:: 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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