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@c  timeSIMHPPA.t,v 1.3 2002/01/17 21:47:46 joel Exp

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@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.