diff options
author | Sebastian Huber <sebastian.huber@embedded-brains.de> | 2021-12-21 16:50:40 +0100 |
---|---|---|
committer | Sebastian Huber <sebastian.huber@embedded-brains.de> | 2022-01-11 09:26:52 +0100 |
commit | e77e04d2dc3794c3e69e023b431a47856fc4af40 (patch) | |
tree | 2fcf64f09323bea345ca92ec7d43a2e050921b4a /c-user | |
parent | cpu-supplement: Add aarch64 to index (diff) | |
download | rtems-docs-e77e04d2dc3794c3e69e023b431a47856fc4af40.tar.bz2 |
c-user: Clarify Clock Manager dependencies
Update #4572.
Diffstat (limited to 'c-user')
-rw-r--r-- | c-user/clock/background.rst | 24 |
1 files changed, 16 insertions, 8 deletions
diff --git a/c-user/clock/background.rst b/c-user/clock/background.rst index 759a976..cffab3c 100644 --- a/c-user/clock/background.rst +++ b/c-user/clock/background.rst @@ -9,20 +9,28 @@ Background Required Support ---------------- -For the features provided by the clock manager to be utilized, periodic timer -interrupts are required. Therefore, a real-time clock or hardware timer is -necessary to create the timer interrupts. The clock tick directive -is normally called by the timer ISR to announce to RTEMS that a system clock -tick has occurred. Elapsed time is measured in ticks. A tick is defined to be -an integral number of microseconds which is specified by the user in the -Configuration Table. +For the features provided by the Clock Manager to be utilized, a :term:`Clock +Driver` is required. The Clock Driver usually provides a clock interrupt which +is serviced on each configured processor at each :term:`clock tick`. In +addition, the Clock Driver provides three clock sources: + +* clock tick + +* :term:`CLOCK_REALTIME` + +* :term:`CLOCK_MONOTONIC` + +The time of these clock sources advances at each clock tick. This yields the +time of the clock sources in a coarse resolution. To get the time of the +``CLOCK_REALTIME`` or ``CLOCK_MONOTONIC`` clock sources in a higher resolution, +the Clock Driver may use a clock device to get the time between clock ticks. .. _Time and Date Data Structures: Time and Date Data Structures ----------------------------- -The clock facilities of the clock manager operate upon calendar time. These +The clock facilities of the Clock Manager operate upon calendar time. These directives utilize the following date and time structure for the native time and date format: |