Method Efficient Task Switching Using NS32381 INTRODUCTION Many m

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Method Efficient Task Switching Using NS32381 INTRODUCTION Many m

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Method Efficient Task Switching Using NS32381
Method Efficient Task Switching Using NS32381
INTRODUCTION Many microprocessor based embedded control systems built real-time multitasking systems where different functions system controlled different tasks multiple tasks such system have appearance executing simultaneously when reality only task running processor time (Readers familiar with concepts tasks multitasking find explanations most general textbooks about operating systems task switch when task stops executing another begins executing task switch usually involves saving values processor's registers onto stack systems where both Central Processor Unit (CPU) Floating Point Unit (FPU) used registers both processors must saved However been used during execution task saving registers onto stack unnecessary undesirable waste time This application brief software designer embedded software system explains detect when been used task task switch time shortened saving registers METHOD Floating Status Register (FRS) (Figure NS32381 Trap Type field (bits 0-2) that records exceptional conditions detected floating point instruction Trap Type field loaded with zero whenever floating point instruction except LFSR (Load Floating Status Register) SFSR (Store Floating Status Register) completes without encountering exception condition Seven Trap Type codes used signal different conditions (including code ``000'' that used indicate ``no exception'') code ``111'' used Loading beginning every task with value that sets Trap Type field unused code ``111'' lets used later determine whether NS32381 been used task Trap Type code task still ``111'' means that floating point instruction been executed since loaded execution figures below refer system that uses NS32381 with National Semiconductor NS32GX32 This method also works with NS32CG16 processor Saving floating point registers onto stack using routine (Figure described below takes clock cycles
National Semiconductor Application Brief Biran April 1989
cases where possible that NS3281 been referenced current task routine (Figure executed prior saving registers This routine takes cycles cases when Floating Point Unit been referenced clock cycles saved been referenced cycles added cycles normal routine (extra These numbers indicate that whenever probability using greater than this method efficient Routine save freg sfsr movl movl movl movl movl movl movl movl FIGURE Routine sfsr andb cmpb save freg sfsr movl movl movl movl movl movl movl movl
FIGURE
NS32381 Status Register (FSR)
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FIGURE
C1995 National Semiconductor Corporation
EE10417
RRD-B30M105 Printed
Method Efficient Task Switching Using NS32381
LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT NATIONAL SEMICONDUCTOR CORPORATION used herein Life support devices systems devices systems which intended surgical implant into body support sustain life whose failure perform when properly used accordance with instructions provided labeling reasonably expected result significant injury user
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critical component component life support device system whose failure perform reasonably expected cause failure life support device system affect safety effectiveness
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National does assume responsibility circuitry described circuit patent licenses implied National reserves right time without notice change said circuitry specifications

Method Efficient Task Switching Using NS32381 INTRODUCTION Many m

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