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docs/utime: Use markup adhering to the latest conventions.

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Paul Sokolovsky 2017-06-25 00:54:38 +03:00
parent 1e31d4bdf6
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@ -57,10 +57,10 @@ Functions
.. function:: sleep(seconds)
Sleep for the given number of seconds. Some boards may accept `seconds` as a
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.
them use `sleep_ms()` and `sleep_us()` functions.
.. function:: sleep_ms(ms)
@ -73,30 +73,32 @@ Functions
.. 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
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
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.
`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
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.
Just like `ticks_ms()` above, but in microseconds.
.. 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 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
@ -111,13 +113,13 @@ Functions
.. 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``
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
(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::
@ -136,23 +138,25 @@ Functions
.. 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
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
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)
`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
[*-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
*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
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
@ -164,10 +168,10 @@ Functions
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:
`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()``::
* 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()
@ -175,7 +179,7 @@ Functions
if time.ticks_diff(time.ticks_us(), start) > 500:
raise TimeoutError
Scheduling events. In this case, ``ticks_diff()`` result may be negative
* Scheduling events. In this case, `ticks_diff()` result may be negative
if an event is overdue::
# This code snippet is not optimized
@ -192,8 +196,8 @@ Functions
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)
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 .
@ -205,8 +209,8 @@ Functions
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.
`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