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