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diff --git a/docs/library/pyb.Timer.rst b/docs/library/pyb.Timer.rst index d2fe9ecbb..ca1d4702e 100644 --- a/docs/library/pyb.Timer.rst +++ b/docs/library/pyb.Timer.rst @@ -3,214 +3,339 @@ class Timer -- control internal timers ====================================== -Timers can be used for a great variety of tasks. At the moment, only -the simplest case is implemented: that of calling a function periodically. +.. only:: port_pyboard + + Timers can be used for a great variety of tasks. At the moment, only + the simplest case is implemented: that of calling a function periodically. + + Each timer consists of a counter that counts up at a certain rate. The rate + at which it counts is the peripheral clock frequency (in Hz) divided by the + timer prescaler. When the counter reaches the timer period it triggers an + event, and the counter resets back to zero. By using the callback method, + the timer event can call a Python function. + + Example usage to toggle an LED at a fixed frequency:: + + tim = pyb.Timer(4) # create a timer object using timer 4 + tim.init(freq=2) # trigger at 2Hz + tim.callback(lambda t:pyb.LED(1).toggle()) + + Example using named function for the callback:: + + def tick(timer): # we will receive the timer object when being called + print(timer.counter()) # show current timer's counter value + tim = pyb.Timer(4, freq=1) # create a timer object using timer 4 - trigger at 1Hz + tim.callback(tick) # set the callback to our tick function + + Further examples:: + + tim = pyb.Timer(4, freq=100) # freq in Hz + tim = pyb.Timer(4, prescaler=0, period=99) + tim.counter() # get counter (can also set) + tim.prescaler(2) # set prescaler (can also get) + tim.period(199) # set period (can also get) + tim.callback(lambda t: ...) # set callback for update interrupt (t=tim instance) + tim.callback(None) # clear callback + + *Note:* Timer 3 is reserved for internal use. Timer 5 controls + the servo driver, and Timer 6 is used for timed ADC/DAC reading/writing. + It is recommended to use the other timers in your programs. + +.. 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 2 16-bit channels and this channels can be tied together to + form 1 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:: + + tim = pyb.Timer(4) # create a timer object using timer 4 + tim.init(mode=Timer.PERIODIC) # initialize it in periodic mode + tim_ch = tim.channel(Timer.A, freq=2) # configure channel A at a frequency of 2Hz + tim_ch.callback(handler=lambda t:led.toggle()) # toggle a LED on every cycle of the timer + + Example using named function for the callback:: + + tim = Timer(1, mode=Timer.PERIODIC) + tim_a = tim.channel(Timer.A, freq=1000) + + led = Pin('GPIO2', af=0, mode=Pin.OUT) + + def tick(timer): # we will receive the timer object when being called + print(timer.time()) # show current timer's time value (is microseconds) + led.toggle() # toggle the LED + + tim_a.callback(handler=tick) + + Further examples:: + + tim1 = pyb.Timer(2, mode=Timer.EVENT_COUNT) # initialize it capture mode + tim2 = pyb.Timer(1, mode=Timer.PWM) # initialize it in PWM mode + 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 + tim_ch = tim2.channel(Timer.B, freq=10000, duty_cycle=50) # start the PWM on channel B with a 50% duty cycle + tim_ch.time() # get the current time in usec (can also be set) + tim_ch.freq(20) # set the frequency (can also get) + tim_ch.duty_cycle(30) # set the duty cycle to 30% (can also get) + tim_ch.duty_cycle(30, Timer.NEGATIVE) # set the duty cycle to 30% and change the polarity to negative + tim_ch.event_count() # get the number of captured events + tim_ch.event_time() # get the the time of the last captured event + tim_ch.period(2000000) # change the period to 2 seconds -Each timer consists of a counter that counts up at a certain rate. The rate -at which it counts is the peripheral clock frequency (in Hz) divided by the -timer prescaler. When the counter reaches the timer period it triggers an -event, and the counter resets back to zero. By using the callback method, -the timer event can call a Python function. - -Example usage to toggle an LED at a fixed frequency:: - - tim = pyb.Timer(4) # create a timer object using timer 4 - tim.init(freq=2) # trigger at 2Hz - tim.callback(lambda t:pyb.LED(1).toggle()) - -Example using named function for the callback:: - - def tick(timer): # we will receive the timer object when being called - print(timer.counter()) # show current timer's counter value - tim = pyb.Timer(4, freq=1) # create a timer object using timer 4 - trigger at 1Hz - tim.callback(tick) # set the callback to our tick function - -Further examples:: - - tim = pyb.Timer(4, freq=100) # freq in Hz - tim = pyb.Timer(4, prescaler=0, period=99) - tim.counter() # get counter (can also set) - tim.prescaler(2) # set prescaler (can also get) - tim.period(199) # set period (can also get) - tim.callback(lambda t: ...) # set callback for update interrupt (t=tim instance) - tim.callback(None) # clear callback - -*Note:* Timer 3 is reserved for internal use. Timer 5 controls -the servo driver, and Timer 6 is used for timed ADC/DAC reading/writing. -It is recommended to use the other timers in your programs. *Note:* Memory can't be allocated during a callback (an interrupt) and so exceptions raised within a callback don't give much information. See :func:`micropython.alloc_emergency_exception_buf` for how to get around this limitation. + Constructors ------------ .. class:: pyb.Timer(id, ...) - Construct a new timer object of the given id. If additional - arguments are given, then the timer is initialised by ``init(...)``. - ``id`` can be 1 to 14, excluding 3. + .. only:: port_pyboard + + Construct a new timer object of the given id. If additional + arguments are given, then the timer is initialised by ``init(...)``. + ``id`` can be 1 to 14, excluding 3. + + .. only:: port_wipy + + Construct a new timer object of the given id. If additional + arguments are given, then the timer is initialised by ``init(...)``. + ``id`` can be 1 to 4. Methods ------- -.. method:: timer.callback(fun) +.. only:: port_pyboard - Set the function to be called when the timer triggers. - ``fun`` is passed 1 argument, the timer object. - If ``fun`` is ``None`` then the callback will be disabled. + .. method:: timer.init(\*, freq, prescaler, period) + + Initialise the timer. Initialisation must be either by frequency (in Hz) + or by prescaler and period:: + + tim.init(freq=100) # set the timer to trigger at 100Hz + tim.init(prescaler=83, period=999) # set the prescaler and period directly + + Keyword arguments: + + - ``freq`` --- specifies the periodic frequency of the timer. You migh also + view this as the frequency with which the timer goes through one complete cycle. + + - ``prescaler`` [0-0xffff] - specifies the value to be loaded into the + timer's Prescaler Register (PSC). The timer clock source is divided by + (``prescaler + 1``) to arrive at the timer clock. Timers 2-7 and 12-14 + have a clock source of 84 MHz (pyb.freq()[2] \* 2), and Timers 1, and 8-11 + have a clock source of 168 MHz (pyb.freq()[3] \* 2). + + - ``period`` [0-0xffff] for timers 1, 3, 4, and 6-15. [0-0x3fffffff] for timers 2 & 5. + Specifies the value to be loaded into the timer's AutoReload + Register (ARR). This determines the period of the timer (i.e. when the + counter cycles). The timer counter will roll-over after ``period + 1`` + timer clock cycles. + + - ``mode`` can be one of: + + - ``Timer.UP`` - configures the timer to count from 0 to ARR (default) + - ``Timer.DOWN`` - configures the timer to count from ARR down to 0. + - ``Timer.CENTER`` - confgures the timer to count from 0 to ARR and + then back down to 0. + + - ``div`` can be one of 1, 2, or 4. Divides the timer clock to determine + the sampling clock used by the digital filters. + + - ``callback`` - as per Timer.callback() + + - ``deadtime`` - specifies the amount of "dead" or inactive time between + transitions on complimentary channels (both channels will be inactive) + for this time). ``deadtime`` may be an integer between 0 and 1008, with + the following restrictions: 0-128 in steps of 1. 128-256 in steps of + 2, 256-512 in steps of 8, and 512-1008 in steps of 16. ``deadime`` + measures ticks of ``source_freq`` divided by ``div`` clock ticks. + ``deadtime`` is only available on timers 1 and 8. + + You must either specify freq or both of period and prescaler. -.. method:: timer.channel(channel, mode, ...) +.. only:: port_wipy - If only a channel number is passed, then a previously initialized channel - object is returned (or ``None`` if there is no previous channel). - - Othwerwise, a TimerChannel object is initialized and returned. - - Each channel can be configured to perform pwm, output compare, or - input capture. All channels share the same underlying timer, which means - that they share the same timer clock. - - Keyword arguments: - - - ``mode`` can be one of: - - - ``Timer.PWM`` --- configure the timer in PWM mode (active high). - - ``Timer.PWM_INVERTED`` --- configure the timer in PWM mode (active low). - - ``Timer.OC_TIMING`` --- indicates that no pin is driven. - - ``Timer.OC_ACTIVE`` --- the pin will be made active when a compare match occurs (active is determined by polarity) - - ``Timer.OC_INACTIVE`` --- the pin will be made inactive when a compare match occurs. - - ``Timer.OC_TOGGLE`` --- the pin will be toggled when an compare match occurs. - - ``Timer.OC_FORCED_ACTIVE`` --- the pin is forced active (compare match is ignored). - - ``Timer.OC_FORCED_INACTIVE`` --- the pin is forced inactive (compare match is ignored). - - ``Timer.IC`` --- configure the timer in Input Capture mode. - - ``Timer.ENC_A`` --- configure the timer in Encoder mode. The counter only changes when CH1 changes. - - ``Timer.ENC_B`` --- configure the timer in Encoder mode. The counter only changes when CH2 changes. - - ``Timer.ENC_AB`` --- configure the timer in Encoder mode. The counter changes when CH1 or CH2 changes. - - - ``callback`` - as per TimerChannel.callback() - - - ``pin`` None (the default) or a Pin object. If specified (and not None) - this will cause the alternate function of the the indicated pin - to be configured for this timer channel. An error will be raised if - the pin doesn't support any alternate functions for this timer channel. + .. 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 for Timer.PWM modes: - - - ``pulse_width`` - determines the initial pulse width value to use. - - ``pulse_width_percent`` - determines the initial pulse width percentage to use. - - Keyword arguments for Timer.OC modes: - - - ``compare`` - determines the initial value of the compare register. - - - ``polarity`` can be one of: + 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.EDGE_TIME`` - Meaure the time pin level changes. + - ``Timer.EDGE_COUNT`` - Count the number of pin level changes. + + - ``width`` must be either 16 or 32 (bits). For really low frequencies <= ~1Hz + (or large periods), 32-bit timers should be used. 32-bit mode is only available + for ``ONE_SHOT`` AND ``PERIODIC`` modes. - - ``Timer.HIGH`` - output is active high - - ``Timer.LOW`` - output is acive low - - Optional keyword arguments for Timer.IC modes: - - - ``polarity`` can be one of: +.. method:: timer.deinit() - - ``Timer.RISING`` - captures on rising edge. - - ``Timer.FALLING`` - captures on falling edge. - - ``Timer.BOTH`` - captures on both edges. - - Note that capture only works on the primary channel, and not on the - complimentary channels. + Deinitialises the timer. - Notes for Timer.ENC modes: + .. only:: port_pyboard + + Disables the callback (and the associated irq). + + Disables any channel callbacks (and the associated irq). + Stops the timer, and disables the timer peripheral. + +.. only:: port_pyboard - - Requires 2 pins, so one or both pins will need to be configured to use - the appropriate timer AF using the Pin API. - - Read the encoder value using the timer.counter() method. - - Only works on CH1 and CH2 (and not on CH1N or CH2N) - - The channel number is ignored when setting the encoder mode. + .. method:: timer.callback(fun) + + Set the function to be called when the timer triggers. + ``fun`` is passed 1 argument, the timer object. + If ``fun`` is ``None`` then the callback will be disabled. + +.. only:: port_pyboard + + .. method:: timer.channel(channel, mode, ...) + + If only a channel number is passed, then a previously initialized channel + object is returned (or ``None`` if there is no previous channel). - PWM Example:: - - timer = pyb.Timer(2, freq=1000) - ch2 = timer.channel(2, pyb.Timer.PWM, pin=pyb.Pin.board.X2, pulse_width=8000) - ch3 = timer.channel(3, pyb.Timer.PWM, pin=pyb.Pin.board.X3, pulse_width=16000) + Othwerwise, a TimerChannel object is initialized and returned. + + Each channel can be configured to perform pwm, output compare, or + input capture. All channels share the same underlying timer, which means + that they share the same timer clock. + + Keyword arguments: + + - ``mode`` can be one of: + + - ``Timer.PWM`` --- configure the timer in PWM mode (active high). + - ``Timer.PWM_INVERTED`` --- configure the timer in PWM mode (active low). + - ``Timer.OC_TIMING`` --- indicates that no pin is driven. + - ``Timer.OC_ACTIVE`` --- the pin will be made active when a compare match occurs (active is determined by polarity) + - ``Timer.OC_INACTIVE`` --- the pin will be made inactive when a compare match occurs. + - ``Timer.OC_TOGGLE`` --- the pin will be toggled when an compare match occurs. + - ``Timer.OC_FORCED_ACTIVE`` --- the pin is forced active (compare match is ignored). + - ``Timer.OC_FORCED_INACTIVE`` --- the pin is forced inactive (compare match is ignored). + - ``Timer.IC`` --- configure the timer in Input Capture mode. + - ``Timer.ENC_A`` --- configure the timer in Encoder mode. The counter only changes when CH1 changes. + - ``Timer.ENC_B`` --- configure the timer in Encoder mode. The counter only changes when CH2 changes. + - ``Timer.ENC_AB`` --- configure the timer in Encoder mode. The counter changes when CH1 or CH2 changes. + + - ``callback`` - as per TimerChannel.callback() + + - ``pin`` None (the default) or a Pin object. If specified (and not None) + this will cause the alternate function of the the indicated pin + to be configured for this timer channel. An error will be raised if + the pin doesn't support any alternate functions for this timer channel. + + Keyword arguments for Timer.PWM modes: + + - ``pulse_width`` - determines the initial pulse width value to use. + - ``pulse_width_percent`` - determines the initial pulse width percentage to use. + + Keyword arguments for Timer.OC modes: + + - ``compare`` - determines the initial value of the compare register. + + - ``polarity`` can be one of: + + - ``Timer.HIGH`` - output is active high + - ``Timer.LOW`` - output is acive low + + Optional keyword arguments for Timer.IC modes: + + - ``polarity`` can be one of: + + - ``Timer.RISING`` - captures on rising edge. + - ``Timer.FALLING`` - captures on falling edge. + - ``Timer.BOTH`` - captures on both edges. + + Note that capture only works on the primary channel, and not on the + complimentary channels. + + Notes for Timer.ENC modes: + + - Requires 2 pins, so one or both pins will need to be configured to use + the appropriate timer AF using the Pin API. + - Read the encoder value using the timer.counter() method. + - Only works on CH1 and CH2 (and not on CH1N or CH2N) + - The channel number is ignored when setting the encoder mode. + + PWM Example:: + + timer = pyb.Timer(2, freq=1000) + ch2 = timer.channel(2, pyb.Timer.PWM, pin=pyb.Pin.board.X2, pulse_width=8000) + ch3 = timer.channel(3, pyb.Timer.PWM, pin=pyb.Pin.board.X3, pulse_width=16000) -.. method:: timer.counter([value]) +.. only:: port_wipy - Get or set the timer counter. + .. 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). + + Othwerwise, 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. -.. method:: timer.deinit() + - ``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``. - Deinitialises the timer. - - Disables the callback (and the associated irq). - Disables any channel callbacks (and the associated irq). - Stops the timer, and disables the timer peripheral. + Keyword only arguments: -.. method:: timer.freq([value]) + - ``freq`` sets the frequency in Hz. + - ``period`` sets the period in microseconds. - Get or set the frequency for the timer (changes prescaler and period if set). + .. note:: -.. method:: timer.init(\*, freq, prescaler, period) + Either ``freq`` or ``period`` must be given, never both. - Initialise the timer. Initialisation must be either by frequency (in Hz) - or by prescaler and period:: - - tim.init(freq=100) # set the timer to trigger at 100Hz - tim.init(prescaler=83, period=999) # set the prescaler and period directly - - Keyword arguments: - - - ``freq`` --- specifies the periodic frequency of the timer. You migh also - view this as the frequency with which the timer goes through one complete cycle. - - - ``prescaler`` [0-0xffff] - specifies the value to be loaded into the - timer's Prescaler Register (PSC). The timer clock source is divided by - (``prescaler + 1``) to arrive at the timer clock. Timers 2-7 and 12-14 - have a clock source of 84 MHz (pyb.freq()[2] \* 2), and Timers 1, and 8-11 - have a clock source of 168 MHz (pyb.freq()[3] \* 2). - - - ``period`` [0-0xffff] for timers 1, 3, 4, and 6-15. [0-0x3fffffff] for timers 2 & 5. - Specifies the value to be loaded into the timer's AutoReload - Register (ARR). This determines the period of the timer (i.e. when the - counter cycles). The timer counter will roll-over after ``period + 1`` - timer clock cycles. - - - ``mode`` can be one of: + - ``polarity`` this is applicable for: + + - ``PWM``, defines the polarity of the duty cycle + - ``EDGE_TIME`` and ``EDGE_COUNT``, defines the polarity of the pin level change to detect. + To detect both rising and falling edges, make ``polarity=Timer.POSITIVE | Timer.NEGATIVE``. + - ``duty_cycle`` only applicable to ``PWM``. It's a percentage (0-100) - - ``Timer.UP`` - configures the timer to count from 0 to ARR (default) - - ``Timer.DOWN`` - configures the timer to count from ARR down to 0. - - ``Timer.CENTER`` - confgures the timer to count from 0 to ARR and - then back down to 0. - - - ``div`` can be one of 1, 2, or 4. Divides the timer clock to determine - the sampling clock used by the digital filters. - - - ``callback`` - as per Timer.callback() - - - ``deadtime`` - specifies the amount of "dead" or inactive time between - transitions on complimentary channels (both channels will be inactive) - for this time). ``deadtime`` may be an integer between 0 and 1008, with - the following restrictions: 0-128 in steps of 1. 128-256 in steps of - 2, 256-512 in steps of 8, and 512-1008 in steps of 16. ``deadime`` - measures ticks of ``source_freq`` divided by ``div`` clock ticks. - ``deadtime`` is only available on timers 1 and 8. - - You must either specify freq or both of period and prescaler. +.. only:: port_pyboard -.. method:: timer.period([value]) + .. method:: timer.counter([value]) - Get or set the period of the timer. + Get or set the timer counter. -.. method:: timer.prescaler([value]) +.. only:: port_pyboard - Get or set the prescaler for the timer. + .. method:: timer.freq([value]) + + Get or set the frequency for the timer (changes prescaler and period if set). -.. method:: timer.source_freq() +.. only:: port_pyboard - Get the frequency of the source of the timer. + .. method:: timer.period([value]) + + Get or set the period of the timer. + + .. method:: timer.prescaler([value]) + + Get or set the prescaler for the timer. + + .. method:: timer.source_freq() + + Get the frequency of the source of the timer. class TimerChannel --- setup a channel for a timer ================================================== @@ -222,37 +347,93 @@ TimerChannel objects are created using the Timer.channel() method. Methods ------- -.. method:: timerchannel.callback(fun) - - Set the function to be called when the timer channel triggers. - ``fun`` is passed 1 argument, the timer object. - If ``fun`` is ``None`` then the callback will be disabled. - -.. method:: timerchannel.capture([value]) - - Get or set the capture value associated with a channel. - capture, compare, and pulse_width are all aliases for the same function. - capture is the logical name to use when the channel is in input capture mode. - -.. method:: timerchannel.compare([value]) +.. only:: port_pyboard + + .. method:: timerchannel.callback(fun) + + Set the function to be called when the timer channel triggers. + ``fun`` is passed 1 argument, the timer object. + If ``fun`` is ``None`` then the callback will be disabled. + +.. only:: port_wipy + + .. method:: timerchannel.callback(\**, value, priority=1, handler=None) + + The behavior of this callback is heaviliy 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.EDGE_COUNT`` the callback is executed when reaching + the configured number of events (see ``value`` param below). + - 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. + - ``value`` is **only valid** when in ``Timer.EDGE_COUNT`` mode and is used to set + the number of edge events that will trigger the interrupt. + + Returns a callback object. + +.. only:: port_pyboard + + .. method:: timerchannel.capture([value]) + + Get or set the capture value associated with a channel. + capture, compare, and pulse_width are all aliases for the same function. + capture is the logical name to use when the channel is in input capture mode. + + .. method:: timerchannel.compare([value]) + + Get or set the compare value associated with a channel. + capture, compare, and pulse_width are all aliases for the same function. + compare is the logical name to use when the channel is in output compare mode. + + .. method:: timerchannel.pulse_width([value]) + + Get or set the pulse width value associated with a channel. + capture, compare, and pulse_width are all aliases for the same function. + pulse_width is the logical name to use when the channel is in PWM mode. + + In edge aligned mode, a pulse_width of ``period + 1`` corresponds to a duty cycle of 100% + In center aligned mode, a pulse width of ``period`` corresponds to a duty cycle of 100% + + .. method:: timerchannel.pulse_width_percent([value]) + + Get or set the pulse width percentage associated with a channel. The value + is a number between 0 and 100 and sets the percentage of the timer period + for which the pulse is active. The value can be an integer or + floating-point number for more accuracy. For example, a value of 25 gives + a duty cycle of 25%. + +.. 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.time([value]) - Get or set the compare value associated with a channel. - capture, compare, and pulse_width are all aliases for the same function. - compare is the logical name to use when the channel is in output compare mode. + Get or set the timer channel current **time** value (in microseconds). + + .. method:: timerchannel.event_count() -.. method:: timerchannel.pulse_width([value]) + Get the number of edge events counted. - Get or set the pulse width value associated with a channel. - capture, compare, and pulse_width are all aliases for the same function. - pulse_width is the logical name to use when the channel is in PWM mode. - - In edge aligned mode, a pulse_width of ``period + 1`` corresponds to a duty cycle of 100% - In center aligned mode, a pulse width of ``period`` corresponds to a duty cycle of 100% + .. method:: timerchannel.event_time() -.. method:: timerchannel.pulse_width_percent([value]) + Get the time of ocurrance of the last event. - Get or set the pulse width percentage associated with a channel. The value - is a number between 0 and 100 and sets the percentage of the timer period - for which the pulse is active. The value can be an integer or - floating-point number for more accuracy. For example, a value of 25 gives - a duty cycle of 25%. + .. method:: timerchannel.duty_cycle([value]) + + Get or set the duty cycle of the PWM signal (in the range of 0-100). |