Date: Mon, 26 Jun 1995 09:37:34 +1000 From: Bruce Evans <bde@zeta.org.au> To: terry@cs.weber.edu, wpaul@skynet.ctr.columbia.edu Cc: hackers@freebsd.org, rgrimes@gndrsh.aac.dev.com Subject: Re: 2.05R reboot hangs Message-ID: <199506252337.JAA10041@godzilla.zeta.org.au>
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>> I seem to recall reading somewhere that there's a BIOS routine that >> can be used for rebooting the system. Now, I know using BIOS calls is a >> ... >This is the keyboard reset line. That's the "BIOS" call. It's the >standard way rests are done (it's how DOS fdisk did it). XTs don't have a BIOS reset. Jumping to the reset vector is the only way for them. fdisk might try both, or something more clever depending on what it is running on. >The problem with the keyboard reset code is (apparently) that the >gate A20 has not been reenabled. Disabled? This seems likely. The linear reset address is not 0xF000:0xFFF0 or whatever I said before; it is actually %eip = 0x0000fff0 + base(%cs) = 0xffff0000 = 0xfffffff0 This has A20 and other high bits set, so it works properly iff the ROM is shadowed in high memory at all times. Does GateA20 control A21-31? Bruce
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