SYSC-3303-13-RTOSInterrupts

SYSC-3303-13-RTOSInterrupts - SYSC 3303 RealTime...

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SYSC 3303 Real Time Programming terrupts and RTOS Interrupts and RTOS “ nterrupt handling one of least well defined Interrupt handling one of least well defined areas in RTOS design” [Xenomai White Paper]
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terrupts Highest H/W Priority . . . Interrupts T pically arrive sporadically Scheduler Priority Lowest H/W Priority yp ca y ae spo ad ca y Interrupt handling Serviced immediately Highest S/W Priority . . . Nonpreemptable What is the effect of interrupt handling on the Lowest S/W Priority determinism of real time threads? H/W interrupts effectively higher priority than any al me thread real time thread H/W interrupts themselves are assigned H/W priorities (by system designer) 3/27/2009 SYSC 3303 Winter 2009 C. Schramm 2
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lit Interrupting Handling Split Interrupting Handling mediate terrupt service (IIS) 1. Immediate interrupt service (IIS) Execute at H/W priority level terrupts disabled by default RT systems: Interrupts disabled by default Interrupt latency = maining time for current instruction + mall fixed) Fast, sure; Predictable, definitely remaining time for current instruction + (small, fixed) (thread) context switch + (small, fixed) (IIS for all other higher priority interrupts) + ig, variable) (big, variable) vectoring to appropriate ISR (small, may be variable) Does not complete interrupt handling 3/27/2009 SYSC 3303 Winter 2009 C. Schramm 3
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lit Interrupting Handling Split Interrupting Handling heduled terrupt Service (SIS) 2. Scheduled Interrupt Service (SIS) Invoked by IIS at suitable S/W priority e.g. LynxOS: Priority of SIS = Priority of thread that opened/init’d the interrupting device
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SYSC-3303-13-RTOSInterrupts - SYSC 3303 RealTime...

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