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diff --git a/docs/library/pyb.Timer.rst b/docs/library/pyb.Timer.rst new file mode 100644 index 0000000000..5d657e871a --- /dev/null +++ b/docs/library/pyb.Timer.rst @@ -0,0 +1,232 @@ +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. + +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()) + +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. + + +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. + + +Methods +------- + +.. 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. + +.. 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). + + 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. + + - ``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. + + PWM Example:: + + timer = pyb.Timer(2, freq=1000) + ch2 = timer.channel(2, pyb.Timer.PWM, pin=pyb.Pin.board.X2, pulse_width=210000) + ch3 = timer.channel(3, pyb.Timer.PWM, pin=pyb.Pin.board.X3, pulse_width=420000) + +.. method:: timer.counter([value]) + + Get or set the timer counter. + +.. method:: timer.deinit() + + 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. + +.. method:: timer.freq([value]) + + Get or set the frequency for the timer (changes prescaler and period if set). + +.. 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.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 +================================================== + +Timer channels are used to generate/capture a signal using a timer. + +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]) + + 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%. |