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author | Christopher Arndt <chris@chrisarndt.de> | 2017-03-05 19:56:36 +0100 |
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committer | Paul Sokolovsky <pfalcon@users.sourceforge.net> | 2017-03-17 20:45:08 +0300 |
commit | 9b80a1e3e93e51fdac8a288de58474e4b26efd46 (patch) | |
tree | d4a6a46d906c3c0010b681b0d0449b847f954489 | |
parent | 5640e6dacd39d97adffce8490991c457f457b1cd (diff) | |
download | micropython-9b80a1e3e93e51fdac8a288de58474e4b26efd46.tar.gz micropython-9b80a1e3e93e51fdac8a288de58474e4b26efd46.zip |
utime module documentation fixes and cleanup:
* Fix mis-spelling of `ticks_add` in code examples.
* Be consistent about parentheses after function names.
* Be consistent about formatting of function, variable and constant names.
* Be consistent about spaces and punctuation.
* Fix some language errors (missing or wrong words, wrong word order).
* Keep line length under 90 chars.
Signed-off-by: Christopher Arndt <chris@chrisarndt.de>
-rw-r--r-- | docs/library/utime.rst | 113 |
1 files changed, 58 insertions, 55 deletions
diff --git a/docs/library/utime.rst b/docs/library/utime.rst index 109c3560cc..0b47a036e6 100644 --- a/docs/library/utime.rst +++ b/docs/library/utime.rst @@ -58,7 +58,7 @@ Functions .. only:: port_unix or port_pyboard or port_esp8266 .. function:: sleep(seconds) - + Sleep for the given number of seconds. Seconds can be a floating-point number to sleep for a fractional number of seconds. Note that other MicroPython ports may not accept floating-point argument, for compatibility with them use ``sleep_ms()`` @@ -67,32 +67,32 @@ Functions .. only:: port_wipy .. function:: sleep(seconds) - + Sleep for the given number of seconds. .. only:: port_unix or port_pyboard or port_wipy or port_esp8266 - .. function:: sleep_ms(ms) + .. function:: sleep_ms(ms) Delay for given number of milliseconds, should be positive or 0. - .. function:: sleep_us(us) + .. function:: sleep_us(us) - Delay for given number of microseconds, should be positive or 0 + Delay for given number of microseconds, should be positive or 0. - .. function:: ticks_ms() + .. function:: ticks_ms() - Returns an increasing millisecond counter with an arbitrary reference point, - that wraps around after some value. This 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. + Returns an increasing millisecond counter with an arbitrary reference point, that + wraps around after some value. This 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 @@ -100,15 +100,15 @@ Functions as arguments to ``ticks_diff()`` or ``ticks_add()`` will also lead to invalid results from the latter functions. - .. function:: ticks_us() + .. function:: ticks_us() - Just like ``ticks_ms`` above, but in microseconds. + Just like ``ticks_ms()`` above, but in microseconds. -.. function:: ticks_cpu() +.. function:: ticks_cpu() - Similar to ``ticks_ms`` and ``ticks_us``, but with the highest possible resolution + 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 a CPU clock, some other timing source available in a + 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 @@ -118,13 +118,13 @@ Functions Availability: Not every port implements this function. -.. function:: ticks_add(ticks, delta) +.. 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 ``tick_ms()``, ``ticks_us()``, ``ticks_cpu()`` functions (or from previous + 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 @@ -133,35 +133,37 @@ Functions Examples:: # Find out what ticks value there was 100ms ago - print(tick_add(time.ticks_ms(), -100)) + print(ticks_add(time.ticks_ms(), -100)) # Calculate deadline for operation and test for it - deadline = tick_add(time.ticks_ms(), 200) + 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(tick_add(0, -1)) - - -.. function:: ticks_diff(ticks1, ticks2) - - Measure ticks difference between values returned from ticks_ms(), ticks_us(), or ticks_cpu() - functions. The argument order is the same as for subtraction operator, - ``tick_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` occured earlier in time than `ticks2`. Otherwise, it means that - `ticks1` occured 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 2 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. + 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. 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`` occured earlier in time than ``ticks2``. Otherwise, it means that + ``ticks1`` occured 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 @@ -200,20 +202,21 @@ Functions print("Oops, running late, tell task to run faster!") task.run(run_faster=true) - Note: Do not pass ``time()`` values to ``ticks_diff()``, and should use + 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. + 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 |