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| -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: |