Changeset e23f46c in rtems-docs


Ignore:
Timestamp:
Jan 30, 2017, 10:31:45 AM (3 years ago)
Author:
Sebastian Huber <sebastian.huber@…>
Branches:
5, master
Children:
a17535d
Parents:
73ad65d
git-author:
Sebastian Huber <sebastian.huber@…> (01/30/17 10:31:45)
git-committer:
Sebastian Huber <sebastian.huber@…> (01/30/17 10:32:24)
Message:

c-user: Update key concepts time

Location:
c-user
Files:
2 edited

Legend:

Unmodified
Added
Removed
  • c-user/configuring_a_system.rst

    r73ad65d re23f46c  
    16511651.. COMMENT: === CONFIGURE_MICROSECONDS_PER_TICK ===
    16521652
    1653 .. _Length of Each Clock Tick:
     1653.. _CONFIGURE_MICROSECONDS_PER_TICK:
    16541654
    16551655Length of Each Clock Tick
  • c-user/key_concepts.rst

    r73ad65d re23f46c  
    246246The development of responsive real-time applications requires an understanding
    247247of how RTEMS maintains and supports time-related operations.  The basic unit of
    248 time in RTEMS is known as a tick.  The frequency of clock ticks is completely
    249 application dependent and determines the granularity and accuracy of all
    250 interval and calendar time operations.
     248time in RTEMS is known as a `clock tick` or simply `tick`.  The tick interval
     249is defined by the application configuration option
     250:ref:`CONFIGURE_MICROSECONDS_PER_TICK <CONFIGURE_MICROSECONDS_PER_TICK>`.  The
     251tick interval defines the basic resolution of all interval and calendar time
     252operations.  Obviously, the directives which use intervals or wall time cannot
     253operate without some external mechanism which provides a periodic clock tick.
     254This clock tick is provided by the clock driver.  The tick precision and
     255stability depends on the clock driver and interrupt latency.  Most clock
     256drivers provide a timecounter to measure the time with a higher resolution than
     257the tick.
    251258
    252259.. index:: rtems_interval
     
    258265time.  For example, when a task delays for an interval of ten ticks, it is
    259266implied that the task will not execute until ten clock ticks have occurred.
    260 All intervals are specified using data type ``rtems_interval``.
     267All intervals are specified using data type :c:type:`rtems_interval`.
    261268
    262269A characteristic of interval timing is that the actual interval period may be a
     
    264271time at which the delay timer is set up occurs at some time between two clock
    265272ticks.  Therefore, the first countdown tick occurs in less than the complete
    266 time interval for a tick.  This can be a problem if the clock granularity is
     273time interval for a tick.  This can be a problem if the tick resolution is
    267274large.
    268275
     
    278285scheduled at an actual calendar date and time.  For example, a task could
    279286request to delay until midnight on New Year's Eve before lowering the ball at
    280 Times Square.  The data type ``rtems_time_of_day`` is used to specify calendar
     287Times Square.  The data type :c:type:`rtems_time_of_day` is used to specify calendar
    281288time in RTEMS services.  See :ref:`Time and Date Data Structures`.
    282289
    283290.. index:: rtems_time_of_day
    284 
    285 Obviously, the directives which use intervals or wall time cannot operate
    286 without some external mechanism which provides a periodic clock tick.  This
    287 clock tick is typically provided by a real time clock or counter/timer device.
    288291
    289292Memory Management
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