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diff --git a/docs/library/utime.rst b/docs/library/utime.rst deleted file mode 100644 index a39f5ee73..000000000 --- a/docs/library/utime.rst +++ /dev/null @@ -1,229 +0,0 @@ -:mod:`utime` -- time related functions -====================================== - -.. module:: utime - :synopsis: time related functions - -|see_cpython_module| :mod:`python:time`. - -The ``utime`` 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. - -Functions ---------- - -.. function:: localtime([secs]) - - Convert a time expressed in seconds since the Epoch (see above) into an 8-tuple which - contains: (year, month, mday, hour, minute, second, weekday, yearday) - If secs is not provided or None, then the current time from the RTC is used. - - * year includes the century (for example 2014). - * month is 1-12 - * mday is 1-31 - * hour is 0-23 - * minute is 0-59 - * second is 0-59 - * weekday is 0-6 for Mon-Sun - * yearday is 1-366 - -.. function:: mktime() - - This is inverse function of localtime. It's argument is a full 8-tuple - which expresses a time as per localtime. It returns an integer which is - the number of seconds since Jan 1, 2000. - -.. function:: sleep(seconds) - - 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. - -.. function:: sleep_ms(ms) - - Delay for given number of milliseconds, should be positive or 0. - -.. function:: sleep_us(us) - - Delay for given number of microseconds, should be positive or 0. - -.. function:: ticks_ms() - - 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. - -.. function:: ticks_us() - - Just like `ticks_ms()` above, but in microseconds. - -.. function:: ticks_cpu() - - Similar to `ticks_ms()` and `ticks_us()`, but with the highest possible resolution - in the system. This is usually CPU clocks, and that's why the function is named that - way. But it doesn't have to be a CPU clock, some other timing source available in a - system (e.g. high-resolution timer) can be used instead. The exact timing unit - (resolution) of this function is not specified on ``utime`` module level, but - documentation for a specific port may provide more specific information. This - function is intended for very fine benchmarking or very tight real-time loops. - Avoid using it in portable code. - - Availability: Not every port implements this function. - - -.. function:: ticks_add(ticks, delta) - - 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)) - - -.. function:: ticks_diff(ticks1, ticks2) - - 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 - behavior: 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(now, scheduled_time) > 0: - print("Too early, let's nap") - sleep_ms(ticks_diff(now, scheduled_time)) - task.run() - elif ticks_diff(now, scheduled_time) == 0: - print("Right at time!") - task.run() - elif ticks_diff(now, scheduled_time) < 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 . - - -.. function:: time() - - Returns the number of seconds, as an integer, since the Epoch, assuming that - underlying RTC is set and maintained as described above. If an RTC is not set, this - function returns number of seconds since a port-specific reference point in time (for - embedded boards without a battery-backed RTC, usually since power up or reset). If you - want to develop portable MicroPython application, you should not rely on this function - to provide higher than second precision. If you need higher precision, use - `ticks_ms()` and `ticks_us()` functions, if you need calendar time, - `localtime()` without an argument is a better choice. - - .. admonition:: Difference to CPython - :class: attention - - In CPython, this function returns number of - seconds since Unix epoch, 1970-01-01 00:00 UTC, as a floating-point, - usually having microsecond precision. With MicroPython, only Unix port - uses the same Epoch, and if floating-point precision allows, - returns sub-second precision. Embedded hardware usually doesn't have - floating-point precision to represent both long time ranges and subsecond - precision, so they use integer value with second precision. Some embedded - hardware also lacks battery-powered RTC, so returns number of seconds - since last power-up or from other relative, hardware-specific point - (e.g. reset). |