Date: Tue, 11 Feb 1997 01:29:00 +0100 From: j@uriah.heep.sax.de (J Wunsch) To: hans@brandinnovators.com (Hans Zuidam) Cc: freebsd-chat@FreeBSD.org, cmott@srv.net Subject: Re: Bus Errors Message-ID: <Mutt.19970211012900.j@uriah.heep.sax.de> In-Reply-To: <199702100848.JAA22878@truk.brandinnovators.com>; from Hans Zuidam on Feb 10, 1997 09:48:15 %2B0100 References: <Pine.BSF.3.91.970209203020.4128A-100000@dolphin.inna.net> <199702100848.JAA22878@truk.brandinnovators.com>
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(Moved to -chat, since it's getting hysterical now...) As Hans Zuidam wrote: > > > What does "Bus error" mean? > > Amazingly enough, a buss error is a memory allocation error. At least it > > was under SunOS. I am guessing FreeBSD is the same on this. > The term "Bus error" originated from the Motorola M68K ... No. Unix hasn't been developed on the m68k. :-) It's been developed on the PDP-11. But you're right, the m68k bus interfaces behave similar to the usual PDP-11 bus interfaces: accesses to bus addresses that are not `wired' will simply hang the bus. The workaround for this was a watchdog timer that caused a processor trap, just the bus error. Looking hard at the signal names, you'll see that the first of them map to the PDP-11 traps. Or does anybody still know what SIGIOT's and SIGEMT's were good for? IIRC, an EMT [emulator trap] has been used to extend the instruction set of the CPU in software, e.g. like an FPU emulator, something that's been invented back in the early days of the PDP-11, too. IOT was the IO trap, i think external devices could hardware-trigger this one when they required attention. There's more PDP-11 inheritage, see spl(9) for another example. In particular, the historic (no longer in BSD) numerical values spl0() through spl7() mapped directly to PDP-11 instructions. -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-)
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