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From: jordan@winvmd.iinus1.ibm.com
Newsgroups: comp.realtime
Subject: Real-Time UNIX: guaranteed context switch times Vs interrupts
Message-ID: <9102181527.AA02102@ucbvax.Berkeley.EDU>
Date: 18 Feb 91 14:26:43 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 20

Novice question: I've read items in the press which state that LynxOS
guarantees a maximum user process context switch time. Steve Daukas of
Harris implies on a previous posting that CX/RT can do the same. Can
anyone explain (without giving away trade secrets) how a UNIX-based
real-time O/S can guarantee context switch time in the presence of
interrupts? Surely interrupts take priority over all user processes? And
a stream of interrupts could potentially delay a context switch
indefinitely.

Also, do these systems allow users to add new interrupt
handlers? If so, are there disclaimers regarding the context switch
time, given that the path length of a user-added interrupt handler is
unknown?

I've got no axe to grind, just curious to understand the truth...

+-----All Views Expressed Are My Own And Are Not Necessarily Shared By------+
+------------------------------My Employer----------------------------------+
Rob Jordan, IBM UK Laboratories, Hursley Park, Winchester, UK.
            jordan@winvmd.iinus1.ibm.com