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@ -9,20 +9,28 @@ Background
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Required Support
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Required Support
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----------------
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----------------
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For the features provided by the clock manager to be utilized, periodic timer
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For the features provided by the Clock Manager to be utilized, a :term:`Clock
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interrupts are required. Therefore, a real-time clock or hardware timer is
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Driver` is required. The Clock Driver usually provides a clock interrupt which
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necessary to create the timer interrupts. The clock tick directive
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is serviced on each configured processor at each :term:`clock tick`. In
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is normally called by the timer ISR to announce to RTEMS that a system clock
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addition, the Clock Driver provides three clock sources:
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tick has occurred. Elapsed time is measured in ticks. A tick is defined to be
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an integral number of microseconds which is specified by the user in the
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* clock tick
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Configuration Table.
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* :term:`CLOCK_REALTIME`
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* :term:`CLOCK_MONOTONIC`
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The time of these clock sources advances at each clock tick. This yields the
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time of the clock sources in a coarse resolution. To get the time of the
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``CLOCK_REALTIME`` or ``CLOCK_MONOTONIC`` clock sources in a higher resolution,
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the Clock Driver may use a clock device to get the time between clock ticks.
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.. _Time and Date Data Structures:
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.. _Time and Date Data Structures:
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Time and Date Data Structures
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Time and Date Data Structures
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-----------------------------
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-----------------------------
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The clock facilities of the clock manager operate upon calendar time. These
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The clock facilities of the Clock Manager operate upon calendar time. These
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directives utilize the following date and time structure for the native time
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directives utilize the following date and time structure for the native time
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and date format:
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and date format:
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