Commit 9b80a1e3 authored by Christopher Arndt's avatar Christopher Arndt Committed by Paul Sokolovsky
Browse files

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: default avatarChristopher Arndt <chris@chrisarndt.de>
parent 5640e6da
......@@ -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
......
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