Date: Tue, 27 Jun 1995 20:30:05 +1000 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, rgrimes@gndrsh.aac.dev.com Cc: hackers@freebsd.org, wpaul@skynet.ctr.columbia.edu Subject: Re: 2.05R reboot hangs Message-ID: <199506271030.UAA04080@godzilla.zeta.org.au>
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>> >jmp 0xffff:0xfff0 is deadly on some machines unless a hard reset has >> >just occured. Many BIOS writers only expected to start executing >> >from that location on a hard reset and do not do full CPU chip >> >initialization. >> >> I think at least [3-4]86's can be initialized sufficiently in software. >There is a world of difference between ``can be'' and ``are'' in the >world of PC bioses and the folks who write them!! You initialize it before jumping to the reset vector. >> Page 0 is free and normally mapped to 0xf0000000. You just have to >> map it to 0 too. >Ewwwweeeee... page 0, the BIOS data page. You want me to try and >call the BIOS from the BIOS data area?? Are you SICK :-) :-) :-) >Bong... try again... oh.. wait, doesnt the BIOS data area end >at 0x500? So I could do what I wanted in say 0x500->0x1000 right?? The whole page is garbage after cold boots. It might be safer to leave 0x400-0x4ff alone in case the BIOS is broken. The interrupt vectors will be corrupted after a dosboot to FreeBSD so you have to rely on the BIOS reinitializing them. Bruce
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