Date: Thu, 3 Sep 1998 15:49:10 -0400 From: sbabkin@dcn.att.com To: weeteck@eecs.umich.edu, freebsd-hackers@FreeBSD.ORG Subject: RE: switching to real-address mode Message-ID: <C50B6FBA632FD111AF0F0000C0AD71EEFF8BC5@dcn71.dcn.att.com>
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Hi, > -----Original Message----- > From: Wee Teck Ng [SMTP:weeteck@eecs.umich.edu] > Sent: Wednesday, September 02, 1998 7:20 PM > To: freebsd-hackers@FreeBSD.ORG > Subject: switching to real-address mode > > i'm trying to switch to real-address mode from protected mode in > the kernel (freebsd 2.2.7), but without success. i had followed > the instructions in the intel manual (p8-14 of system prog guide), > but my code always hung after clearing PE flag in CR0. i would > appreciate comments from anyone who have done this before. > I have tried to this thing once, but only during system boot-up time because later the interrupt handling gets too complicated. May be I still can find this code if you are interested in it. First, you need to allocate a page that has the same physical and virtual address, I have just modified slightly the VM code to reserve such a page during boot-up. Second, you have to disable the interrupts until you set up proper interrupt handlers in real mode. My code switched well to real mode and back, but the support of interrupts was very and very limited, not enough to run the BIOS calls (for what all this code intended). -Sergey To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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