class TimerWiPy – control hardware timers

Note

This class is a non-standard Timer implementation for the WiPy. It is available simply as machine.Timer on the WiPy but is named in the documentation below as machine.TimerWiPy to distinguish it from the more general machine.Timer class.

Hardware timers deal with timing of periods and events. Timers are perhaps the most flexible and heterogeneous kind of hardware in MCUs and SoCs, differently greatly from a model to a model. MicroPython’s Timer class defines a baseline operation of executing a callback with a given period (or once after some delay), and allow specific boards to define more non-standard behaviour (which thus won’t be portable to other boards).

See discussion of important constraints on Timer callbacks.

Note

Memory can’t be allocated inside irq handlers (an interrupt) and so exceptions raised within a handler don’t give much information. See micropython.alloc_emergency_exception_buf() for how to get around this limitation.

Constructors

class machine.TimerWiPy(id, ...)

Construct a new timer object of the given id. Id of -1 constructs a virtual timer (if supported by a board).

Methods

TimerWiPy.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:

    • TimerWiPy.ONE_SHOT - The timer runs once until the configured period of the channel expires.

    • TimerWiPy.PERIODIC - The timer runs periodically at the configured frequency of the channel.

    • TimerWiPy.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.

TimerWiPy.deinit()

Deinitialises the timer. Stops the timer, and disables the timer peripheral.

TimerWiPy.channel(channel, **, freq, period, polarity=TimerWiPy.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

timerchannel.irq(*, trigger, priority=1, handler=None)

The behaviour of this callback is heavily dependent on the operating mode of the timer channel:

  • If mode is TimerWiPy.PERIODIC the callback is executed periodically with the configured frequency or period.

  • If mode is TimerWiPy.ONE_SHOT the callback is executed once when the configured timer expires.

  • If mode is TimerWiPy.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 TimerWiPy.TIMEOUT when the operating mode is either TimerWiPy.PERIODIC or TimerWiPy.ONE_SHOT. In the case that mode is TimerWiPy.PWM then trigger must be equal to TimerWiPy.MATCH.

Returns a callback object.

timerchannel.freq([value])

Get or set the timer channel frequency (in Hz).

timerchannel.period([value])

Get or set the timer channel period (in microseconds).

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

TimerWiPy.ONE_SHOT
TimerWiPy.PERIODIC

Timer operating mode.