[PATCH 1/2] c-user: Clarify Clock Manager dependencies
Sebastian Huber
sebastian.huber at embedded-brains.de
Tue Dec 21 16:01:13 UTC 2021
Update #4572.
---
c-user/clock/background.rst | 24 ++++++++++++++++--------
1 file 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:
--
2.31.1
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