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| | These terms do not state a common model for time measurements. I believe it is relatively well-established | | These terms do not state a common model for time measurements. I believe it is relatively well-established |
| | that the following events and time periods are of interest when measuring realtime performance: | | that the following events and time periods are of interest when measuring realtime performance: |
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| − | == Events ==
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| − | * A - hardware interrupt assertion
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| − | ** This is the time when the hardware interrupt line for an event is raised
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| − | * B - Interrupt service routine starts execution
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| − | * C - Process starts execution
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| − | * D - Result is received from processing the event
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| − | == Time Periods ==
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| − | Real time performance is often expressed in terms of the maximum, minimum and average duration
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| − | for certain time periods defined by the events above.
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| − | Here are some common terms, expressed relative to those events:
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| − | ; Interrupt latency : The time from A to B
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| − | ; Scheduling latency : The time from B to C (this is sometimes referred to as the time from A to C)
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| − | ; Processing time : The time from C to D
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| − | ; Response latency : The time from A to D
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| − | Often, these or similar terms are used with less accuracy to describe the closest
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| − | approximation one can get to these, with a particular test framework and instrumentation set.
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| − | For example, Response latency may be reported as "response time", and refer to the time from
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| − | when a host program records the time, previous to transmitting a piece of data which will cause
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| − | an interrupt on the target machine, to the time when a host program records the time after
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| − | receiving some signal from the target that processing is completed. Of course, time is taken
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| − | in the operations of recording time, tranmissing data, and detecting signals on the host machine.
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| − | But it may be that timing these individual operations at a finer granularity requires
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| − | instrumentation or hardware support not reasonably available for a test.
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