Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site oakhill.UUCP Path: utzoo!watmath!clyde!bonnie!akgua!whuxlm!harpo!decvax!genrad!panda!talcott!harvard!seismo!ut-sally!oakhill!cruess From: cruess@oakhill.UUCP (Michael Cruess) Newsgroups: net.micro.68k Subject: Re: Latest MC68020 bug list by request (now MC68881) Message-ID: <496@oakhill.UUCP> Date: Thu, 22-Aug-85 12:17:14 EDT Article-I.D.: oakhill.496 Posted: Thu Aug 22 12:17:14 1985 Date-Received: Sun, 25-Aug-85 01:29:38 EDT References: <483@oakhill.UUCP> <5883@utzoo.UUCP> Reply-To: cruess@oakhill.UUCP (Michael Cruess) Organization: Motorola Inc. Austin, Tx Lines: 23 More of the story: The MC68881 can save 180 bytes of internal data on a context switch. This only occurs on remainder, trancendental function, and BCD conversion instructions if the save operation occurs during their middle phase of operation. At all other times the idle save format is used, which contains 24 bytes of internal state. In other words, unless your floating point mix is heavily weighed to doing remainders or trancendentals, you get the short format much more frequently. Even so, consider that the execution time of some of these instructions is data dependent, and that the floating point instruction can continue to run (and may complete) while other work pertaining to the context switch is done by the CPU. Yes, you have to reserve the 180 bytes per task just in case. Michael Cruess oakhill!cruess Motorola, Inc. Microprocessor Products Group