Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!tut.cis.ohio-state.edu!ucbvax!mtxinu!taniwha!paul From: paul@taniwha.UUCP (Paul Campbell) Newsgroups: comp.arch Subject: Re: Instruction (dis)continuation Message-ID: <408@taniwha.UUCP> Date: 29 Aug 89 15:07:00 GMT References: <1989Aug24.215104.156@mentor.com> <231@ssp1.idca.tds.philips.nl> <2345@oakhill.UUCP> <204@bbxeng.UUCP> Reply-To: paul@taniwha.UUCP (Paul Campbell) Organization: Taniwha Systems Design, Oakland Lines: 31 In article <204@bbxeng.UUCP> scott@bbxeng.UUCP (Scott-Engineering) writes: > >Forgive me for showing my ignorance, but, doesn't instruction continuation >enable features such as dynamic stack allocation? Are we doomed to >return to the antiquated "stack probe"? Does this mean that 68030 >(user mode) software will not always work correctly on the 68040? >What about page faults? Is the operating system *really* expected >to include an instruction set interpreter so it can simulate >instruction continuation? The 386 is suddenly starting to look good >me. No - the need for 'stack probe' etc was caused by the 68000 (fixed in the 68010) which couldn't restart (either restart or continue) from a bus error (page fault) [it didn't keep enough information around in its bus error stack frame to tell what it had done, or undo it itself while delivering the bus error]. Some early vendors actually had 2 68000s, one which executed the user mode code and was halted in mid instruction while the other was started to fix the problem ..... thus preserving the internal state .... I'm sure Motorola won't make this mistake again ..... Paul -- Paul Campbell UUCP: ..!mtxinu!taniwha!paul AppleLink: D3213 "Free Market": n. (colloq.) a primitive fertility goddess worshipped by an obscure cult in the late 20th C. It's chief priest 'Dow Jones' was eventually lynched by an enraged populace during an economic downturn (early 21st C).