""" time related functions Descriptions taken from `https://raw.githubusercontent.com/micropython/micropython/master/docs/library/time.rst`, etc. ===================================== .. module:: time :synopsis: time related functions |see_cpython_module| :mod:`python:time`. The ``time`` module provides functions for getting the current time and date, measuring time intervals, and for delays. **Time Epoch**: Unix port uses standard for POSIX systems epoch of 1970-01-01 00:00:00 UTC. However, embedded ports use epoch of 2000-01-01 00:00:00 UTC. **Maintaining actual calendar date/time**: This requires a Real Time Clock (RTC). On systems with underlying OS (including some RTOS), an RTC may be implicit. Setting and maintaining actual calendar time is responsibility of OS/RTOS and is done outside of MicroPython, it just uses OS API to query date/time. On baremetal ports however system time depends on ``machine.RTC()`` object. The current calendar time may be set using ``machine.RTC().datetime(tuple)`` function, and maintained by following means: * By a backup battery (which may be an additional, optional component for a particular board). * Using networked time protocol (requires setup by a port/user). * Set manually by a user on each power-up (many boards then maintain RTC time across hard resets, though some may require setting it again in such case). If actual calendar time is not maintained with a system/MicroPython RTC, functions below which require reference to current absolute time may behave not as expected. """ __author__ = "Howard C Lovatt" __copyright__ = "Howard C Lovatt, 2020 onwards." __license__ = "MIT https://opensource.org/licenses/MIT (as used by MicroPython)." __version__ = "7.1.0" # Version set by https://github.com/hlovatt/tag2ver from typing import Final, Optional, Tuple, TypeVar class _TicksMs: ... class _TicksUs: ... class _TicksCPU: ... _Ticks: Final = TypeVar("_Ticks", _TicksMs, _TicksUs, _TicksCPU, int) def sleep(seconds: float, /) -> None: """ Sleep for the given number of seconds. Some boards may accept *seconds* as a floating-point number to sleep for a fractional number of seconds. Note that other boards may not accept a floating-point argument, for compatibility with them use `sleep_ms()` and `sleep_us()` functions. """ def sleep_ms(ms: int, /) -> None: """ Delay for given number of milliseconds, should be positive or 0. This function will delay for at least the given number of milliseconds, but may take longer than that if other processing must take place, for example interrupt handlers or other threads. Passing in 0 for *ms* will still allow this other processing to occur. Use `sleep_us()` for more precise delays. """ def sleep_us(us: int, /) -> None: """ Delay for given number of microseconds, should be positive or 0. This function attempts to provide an accurate delay of at least *us* microseconds, but it may take longer if the system has other higher priority processing to perform. """ def ticks_ms() -> _TicksMs: """ Returns an increasing millisecond counter with an arbitrary reference point, that wraps around after some value. The wrap-around value is not explicitly exposed, but we will refer to it as *TICKS_MAX* to simplify discussion. Period of the values is *TICKS_PERIOD = TICKS_MAX + 1*. *TICKS_PERIOD* is guaranteed to be a power of two, but otherwise may differ from port to port. The same period value is used for all of `ticks_ms()`, `ticks_us()`, `ticks_cpu()` functions (for simplicity). Thus, these functions will return a value in range [*0* .. *TICKS_MAX*], inclusive, total *TICKS_PERIOD* values. Note that only non-negative values are used. For the most part, you should treat values returned by these functions as opaque. The only operations available for them are `ticks_diff()` and `ticks_add()` functions described below. Note: Performing standard mathematical operations (+, -) or relational operators (<, <=, >, >=) directly on these value will lead to invalid result. Performing mathematical operations and then passing their results as arguments to `ticks_diff()` or `ticks_add()` will also lead to invalid results from the latter functions. """ def ticks_us() -> _TicksUs: """ Just like `ticks_ms()` above, but in microseconds. """ def ticks_add(ticks: _Ticks, delta: int, /) -> _Ticks: """ Offset ticks value by a given number, which can be either positive or negative. Given a *ticks* value, this function allows to calculate ticks value *delta* ticks before or after it, following modular-arithmetic definition of tick values (see `ticks_ms()` above). *ticks* parameter must be a direct result of call to `ticks_ms()`, `ticks_us()`, or `ticks_cpu()` functions (or from previous call to `ticks_add()`). However, *delta* can be an arbitrary integer number or numeric expression. `ticks_add()` is useful for calculating deadlines for events/tasks. (Note: you must use `ticks_diff()` function to work with deadlines.) Examples:: # Find out what ticks value there was 100ms ago print(ticks_add(time.ticks_ms(), -100)) # Calculate deadline for operation and test for it deadline = ticks_add(time.ticks_ms(), 200) while ticks_diff(deadline, time.ticks_ms()) > 0: do_a_little_of_something() # Find out TICKS_MAX used by this port print(ticks_add(0, -1)) """ def ticks_diff(ticks1: _Ticks, ticks2: _Ticks, /) -> int: """ Measure ticks difference between values returned from `ticks_ms()`, `ticks_us()`, or `ticks_cpu()` functions, as a signed value which may wrap around. The argument order is the same as for subtraction operator, ``ticks_diff(ticks1, ticks2)`` has the same meaning as ``ticks1 - ticks2``. However, values returned by `ticks_ms()`, etc. functions may wrap around, so directly using subtraction on them will produce incorrect result. That is why `ticks_diff()` is needed, it implements modular (or more specifically, ring) arithmetics to produce correct result even for wrap-around values (as long as they not too distant inbetween, see below). The function returns **signed** value in the range [*-TICKS_PERIOD/2* .. *TICKS_PERIOD/2-1*] (that's a typical range definition for two's-complement signed binary integers). If the result is negative, it means that *ticks1* occurred earlier in time than *ticks2*. Otherwise, it means that *ticks1* occurred after *ticks2*. This holds **only** if *ticks1* and *ticks2* are apart from each other for no more than *TICKS_PERIOD/2-1* ticks. If that does not hold, incorrect result will be returned. Specifically, if two tick values are apart for *TICKS_PERIOD/2-1* ticks, that value will be returned by the function. However, if *TICKS_PERIOD/2* of real-time ticks has passed between them, the function will return *-TICKS_PERIOD/2* instead, i.e. result value will wrap around to the negative range of possible values. Informal rationale of the constraints above: Suppose you are locked in a room with no means to monitor passing of time except a standard 12-notch clock. Then if you look at dial-plate now, and don't look again for another 13 hours (e.g., if you fall for a long sleep), then once you finally look again, it may seem to you that only 1 hour has passed. To avoid this mistake, just look at the clock regularly. Your application should do the same. "Too long sleep" metaphor also maps directly to application behaviour: don't let your application run any single task for too long. Run tasks in steps, and do time-keeping inbetween. `ticks_diff()` is designed to accommodate various usage patterns, among them: * Polling with timeout. In this case, the order of events is known, and you will deal only with positive results of `ticks_diff()`:: # Wait for GPIO pin to be asserted, but at most 500us start = time.ticks_us() while pin.value() == 0: if time.ticks_diff(time.ticks_us(), start) > 500: raise TimeoutError * Scheduling events. In this case, `ticks_diff()` result may be negative if an event is overdue:: # This code snippet is not optimized now = time.ticks_ms() scheduled_time = task.scheduled_time() if ticks_diff(scheduled_time, now) > 0: print("Too early, let's nap") sleep_ms(ticks_diff(scheduled_time, now)) task.run() elif ticks_diff(scheduled_time, now) == 0: print("Right at time!") task.run() elif ticks_diff(scheduled_time, now) < 0: print("Oops, running late, tell task to run faster!") task.run(run_faster=true) Note: Do not pass `time()` values to `ticks_diff()`, you should use normal mathematical operations on them. But note that `time()` may (and will) also overflow. This is known as https://en.wikipedia.org/wiki/Year_2038_problem . """