Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!spool.mu.edu!uwm.edu!bionet!agate!ucbvax!bloom-beacon!eru!hagbard!sunic!mcsun!ukc!acorn!agodwin From: agodwin@acorn.co.uk (Adrian Godwin) Newsgroups: comp.sys.3b1 Subject: Re: Hardware freaks Unite (on this one) Keywords: 3B1, cache, hardware project suggestion. Message-ID: <6464@acorn.co.uk> Date: 18 Apr 91 13:40:38 GMT References: <1991Mar26.023948.3966@i88.isc.com> <6386@acorn.co.uk> <100@fbits.ttank.com> Organization: Acorn Computers Ltd, Cambridge, UK Lines: 41 In article <100@fbits.ttank.com> Mariusz@fbits.ttank.com (Mariusz Stanczak) writes: >In article <6386@acorn.co.uk>, agodwin@acorn.co.uk (Adrian Godwin) writes: >> A number of companies sell daughter boards - some of them based on the >> Motorola app. note - as an upgrade for the Commodore Amiga. It seems to > > Yes, so do others for the Mac... the question for me would be > are those boards system specific, i.e. do they assume (and "solve") > anything about the hardware/software quirks of the given system > for which they are marketed? They may assume things about the bus timing - the critical timings on one system may differ from those on another, and these add-ons aren't going to be as well specified as say, an emulator. One card I know of adds some memory at a fixed address (though it might be possible to change it with a different PAL) - however, it does it at an address that can't exist on a 24-bit-address 68000 so it can't possibly conflict. Control registers may - or may not - be similar. >> inside an A500, they may be useable on the 3b1. This would at least reduce >> the problem to the software part [...] > > So, as above... what would be the pitfals(sp). If such a "card" > wouldn't be hardware specific, and (correct me anybody) since most As I understand it, mostly to the kernel. The higher 680x0 processors have a different interrupt/exception stack frame to the 68000, and the system needs also to recognise memory that isn't in it's normal addressing range. A different mechanism is used to load the PSR. Perhaps there are other differences too - it's only a drop-in replacement for the Amiga because its OS knows about alternative processors. Even so, some applications do things they shouldn't, and fall over. This should be less of a problem on the 3b1, because Unix applications are much better behaved than those for OSs without process protection - but don't forget to fix the diagnostics as well as the real OS ! Or use an upgrade card that makes it possible to switch between a 68020 and a real 68000. -- -------------------------------------------------------------------------- Adrian Godwin (agodwin@acorn.co.uk)