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196 lines
7.7 KiB
196 lines
7.7 KiB
.. _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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.. note::
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Contrary with the rest of the API, timer IDs start at 1, not a t zero. This is because
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the ``Timer`` API is still provisional. A new MicroPython wide API will come soon.
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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 2 16-bit channels and this channels can be tied together to
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form 1 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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tim = Timer(4) # create a timer object using timer 4
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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=2) # configure channel A at a frequency of 2Hz
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tim_ch.callback(handler=lambda t:led.toggle()) # 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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tim = Timer(1, mode=Timer.PERIODIC)
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tim_a = tim.channel(Timer.A, freq=1000)
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led = Pin('GPIO2', mode=Pin.OUT)
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def tick(timer): # we will receive the timer object when being called
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print(timer.time()) # show current timer's time value (is microseconds)
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led.toggle() # toggle the LED
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tim_a.callback(handler=tick)
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Further examples::
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from machine import Timer
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tim1 = Timer(2, mode=Timer.EVENT_COUNT) # initialize it capture mode
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tim2 = Timer(1, mode=Timer.PWM) # initialize it in PWM mode
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tim_ch = tim1.channel(Timer.A, freq=1, polarity=Timer.POSITIVE) # start the event counter with a frequency of 1Hz and triggered by positive edges
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tim_ch = tim2.channel(Timer.B, freq=10000, duty_cycle=50) # start the PWM on channel B with a 50% duty cycle
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tim_ch.time() # get the current time in usec (can also be set)
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tim_ch.freq(20) # set the frequency (can also get)
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tim_ch.duty_cycle(30) # set the duty cycle to 30% (can also get)
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tim_ch.duty_cycle(30, Timer.NEGATIVE) # set the duty cycle to 30% and change the polarity to negative
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tim_ch.event_count() # get the number of captured events
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tim_ch.event_time() # get the the time of the last captured event
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tim_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. If additional
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arguments are given, then the timer is initialised by ``init(...)``.
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``id`` can be 1 to 4.
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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.EDGE_TIME`` - Meaure the time pin level changes.
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- ``Timer.EDGE_COUNT`` - Count the number of pin level changes.
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- ``width`` must be either 16 or 32 (bits). For really low frequencies <= ~1Hz
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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:
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- ``PWM``, defines the polarity of the duty cycle
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- ``EDGE_TIME`` and ``EDGE_COUNT``, defines the polarity of the pin level change to detect.
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To detect both rising and falling edges, make ``polarity=Timer.POSITIVE | Timer.NEGATIVE``.
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- ``duty_cycle`` only applicable to ``PWM``. It's a percentage (0-100)
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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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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.time([value])
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Get or set the timer channel current **time** value (in microseconds).
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.. method:: timerchannel.event_count()
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Get the number of edge events counted.
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.. method:: timerchannel.event_time()
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Get the time of ocurrance of the last event.
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.. method:: timerchannel.duty_cycle([value])
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Get or set the duty cycle of the PWM signal (in the range of 0-100).
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