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authorJoel Sherrill <joel.sherrill@OARcorp.com>1998-10-19 17:46:54 +0000
committerJoel Sherrill <joel.sherrill@OARcorp.com>1998-10-19 17:46:54 +0000
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+@c
+@c COPYRIGHT (c) 1988-1998.
+@c On-Line Applications Research Corporation (OAR).
+@c All rights reserved.
+@c
+@c $Id$
+@c
+
+@chapter HP-7100 Timing Data
+
+@section Introduction
+
+The timing data for the PA-RISC version of RTEMS is
+provided along with the target dependent aspects concerning the
+gathering of the timing data. The hardware platform used to
+gather the times is described to give the reader a better
+understanding of each directive time provided. Also, provided
+is a description of the interrupt latency and the context
+switch times as they pertain to the PA-RISC version of RTEMS.
+
+@section Hardware Platform
+
+No directive execution times are reported for the
+HP-7100 because the target platform was proprietary and
+executions times could not be released.
+
+@section Interrupt Latency
+
+The maximum period with traps disabled or the
+processor interrupt level set to it's highest value inside RTEMS
+is less than RTEMS_MAXIMUM_DISABLE_PERIOD
+microseconds including the instructions which
+disable and re-enable interrupts. The time required for the
+HP-7100 to vector an interrupt and for the RTEMS entry overhead
+before invoking the user's trap handler are a total of
+RTEMS_INTR_ENTRY_RETURNS_TO_PREEMPTING_TASK
+microseconds. These combine to yield a worst case interrupt
+latency of less than RTEMS_MAXIMUM_DISABLE_PERIOD +
+RTEMS_INTR_ENTRY_RETURNS_TO_PREEMPTING_TASK microseconds at 15 Mhz.
+[NOTE: The maximum period with interrupts disabled was last
+determined for Release RTEMS_RELEASE_FOR_MAXIMUM_DISABLE_PERIOD.]
+
+It should be noted again that the maximum period with
+interrupts disabled within RTEMS for the HP-7100 is hand calculated.
+
+@section Context Switch
+
+The RTEMS processor context switch time is RTEMS_NO_FP_CONTEXTS
+microsections for the HP-7100 when no floating point context
+switch is saved or restored. Saving and restoring the floating
+point context adds additional time to the context
+switch procedure. Additional execution time is required when a
+TASK_SWITCH user extension is configured. The use of the
+TASK_SWITCH extension is application dependent. Thus, its
+execution time is not considered part of the raw context switch
+time.
+
+Since RTEMS was designed specifically for embedded
+missile applications which are floating point intensive, the
+executive is optimized to avoid unnecessarily saving and
+restoring the state of the numeric coprocessor. On many
+processors, the state of the numeric coprocessor is only saved
+when an FLOATING_POINT task is dispatched and that task was not
+the last task to utilize the coprocessor. In a system with only
+one FLOATING_POINT task, the state of the numeric coprocessor
+will never be saved or restored. When the first FLOATING_POINT
+task is dispatched, RTEMS does not need to save the current
+state of the numeric coprocessor. As discussed in the Register
+Usage section, on the HP-7100 the every task is considered to be
+floating point registers and , as a rsule, every context switch
+involves saving and restoring the state of the floating point
+unit.
+
+The following table summarizes the context switch
+times for the HP-7100 processor:
+
+@example
+no times are available for the HP-7100
+@end example
+
+@section Directive Times
+
+No execution times are available for the HP-7100
+because the target platform was proprietary and no timing
+information could be released.
+