OpenBIOS July 1999

openbios@openbios.org

27 participants
30 discussions

RE: [OpenBIOS] Why protected mode?
by Winter Jörg 15 Jul '99

15 Jul '99

> ---------- > From: Timothy J. Massey[SMTP:tmassey@iname.com] > Sent: Donnerstag, 15. Juli 1999 21:08 > To: openbios(a)elvis.informatik.uni-freiburg.de > Subject: Re: [OpenBIOS] Why protected mode? > ...... Sorry, but ... ... hey guys are you shure you´re in the right discussion group? this is bios, not architecture ... (and after all, Int*l keeps doing strange things for years now. Why worry? ;-) ...... greetinx, Jake. - To Unsubscribe: send mail to majordomo(a)freiburg.linux.de with "unsubscribe openbios" in the body of the message

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Re: [OpenBIOS] Why protected mode?
by Timothy J. Massey 15 Jul '99

15 Jul '99

On Thu, 15 Jul 1999 12:31:48 -0400 (EDT), Kevin P Lawton wrote: >Also IMHO, by far their greatest mistake in history >was when they went to a new protected mode environment >in the 286, they carried forward the segmentation >architecture. But they had to. The 286 is a 16-bit processor. Without segmented memory, you would be limited to 64k of memory... Leaving protected mode out of it, the rest of the 286 was merely an evolution of the 80186: a change from a 20-bit memory bus to a 24-bit. That's the only real change. Of course, there *is* protected mode... Only with a 32-bit processor can you realistically eliminate segmented memory. Tim Massey - To Unsubscribe: send mail to majordomo(a)freiburg.linux.de with "unsubscribe openbios" in the body of the message

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Re: [OpenBIOS] Why protected mode?
by Timothy J. Massey 15 Jul '99

15 Jul '99

On Thu, 15 Jul 1999 20:42:27 +0200 (CEST), Matthias W�chter wrote: >On Thu, 15 Jul 1999, Timothy J. Massey wrote: > >> Only with a 32-bit processor can you realistically eliminate segmented >> memory. > >Don't say that: There are some Xeon motherboards around (well, most of >them are sold in complete supported systems) supporting 16GB of memory and >more. Since you need more than 32 bits to address this space, they had to >design work-arounds like segmentation (I don't know anything more about >it). Even worse: The switching is done externally, by the chipset... That only makes my point even more. In that case, even 32-bit memory paths are not enough. If a 32-bit bus won't do it, why would you even attempt it with a 16-bit CPU? I'm not saying that 32 bits is all you need. What I'm saying is that you need at *least* 32 bits! Tim Massey - To Unsubscribe: send mail to majordomo(a)freiburg.linux.de with "unsubscribe openbios" in the body of the message

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Re: [OpenBIOS] Why protected mode?
by Phil King 15 Jul '99

15 Jul '99

At 05:28 PM 7/7/99 -0700, you wrote: >>> 2) Go into protected mode for initial configuration, then exit it to load >>> the boot code (note that the BIOS service routines would have to run in >>> real mode in this case). >> >>This is how other BIOSs today do it. That is also how you have to do if >>you strive for IBM-PC BIOS compability. > >And this continues the necessity for either a keyboard or a keyboard >simulator, does it not? My recollection is that the only way out of >protected mode (back in 286 days) was through a keyboard reset sequence. That was only on the '286, which required a processor reset to get back into real mode and was assisted by the keyboard controller, one of the Great PC Hacks. It is not as traumatic with '386 and beyond. Cheers! Phil King pking(a)netschools.net - To Unsubscribe: send mail to majordomo(a)freiburg.linux.de with "unsubscribe openbios" in the body of the message

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Re: [OpenBIOS] Why protected mode?
by William Meyer 15 Jul '99

15 Jul '99

>I also wanted to add that all this nonsense was necessary because int he >design of the 80286 there was a method of ENTERing protected mode, but no >clean way to get back. I'm curious to know whether the double/triple fault >was used as a way back because that's how Intel had *designed* it, or if the >lack of method to come back to Real mode was an oversight. Thinking back, I recall an article which discussed the one way process, and offered no alternative to the keyboard kludge. As the author seemed well versed in the inner essence of the 286, I tend to thing that your multiple fault method was discovered later, as a head-smacking sort of experience. William Meyer MATCO www.matco-video.com - To Unsubscribe: send mail to majordomo(a)freiburg.linux.de with "unsubscribe openbios" in the body of the message

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Re: [OpenBIOS] Why protected mode?
by Timothy J. Massey 15 Jul '99

15 Jul '99

On Thu, 15 Jul 1999 08:39:45 -0400, Andrew Kohlsmith wrote: >> > That was only on the '286, which required a processor reset to get back >> > into real mode and was assisted by the keyboard controller, one of the >> > Great PC Hacks. It is not as traumatic with '386 and beyond. > >I also wanted to add that all this nonsense was necessary because int he >design of the 80286 there was a method of ENTERing protected mode, but no >clean way to get back. I'm curious to know whether the double/triple fault >was used as a way back because that's how Intel had *designed* it, or if the >lack of method to come back to Real mode was an oversight. > >Looking at pages like x86.org, I tend to think the latter. Definitely a mistake. Well, let's say shortsighted thinking from Intel. They thought, "Once in protected mode, who would want to go back to real mode?" In fact, that was one big reason why OS/2 version 1.x was slow and unreliable when it came to DOS programs. Resetting the processor to real mode on the 286 had been described by Intel as "Putting a car's transmission into reverse at 50 miles per hour". (That and the lack of hardware virtualization via the IO map...) Of course, unless we're writing a bios for 286 computers, that's all a moot point! :) But an interesting piece of trivia nonetheless. Tim Massey - To Unsubscribe: send mail to majordomo(a)freiburg.linux.de with "unsubscribe openbios" in the body of the message

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[Fwd: Re: [OpenBIOS] Why protected mode?]
by Andrew Kohlsmith 15 Jul '99

15 Jul '99

for some reason this message didn't make it ot the list... Andrew -------- Original Message -------- Subject: Re: [OpenBIOS] Why protected mode? Date: Thu, 15 Jul 1999 08:20:22 -0400 From: Andrew Kohlsmith <akohlsmith(a)benshaw.com> Organization: Benshaw, Inc. To: openbios(a)elvis.informatik.uni-freiburg.de References: <3.0.32.19990707182234.01c84ec0(a)pop.netschools.net> > >simulator, does it not? My recollection is that the only way out of > >protected mode (back in 286 days) was through a keyboard reset sequence. > > That was only on the '286, which required a processor reset to get back > into real mode and was assisted by the keyboard controller, one of the > Great PC Hacks. It is not as traumatic with '386 and beyond. Actually that was the kludge to fix it. The *really* savvy way to do it was a triple fault. Something along the lines (going from memory here) like trashing the stack and executing an illegal instruction. The processor would take exception to the illegal instruction (fault 1), go to push CS,IP,F to the stack, which wasn't there (fault 2), cause exception to that and go to push them again (fault 3) so it would reset. Thousands of times faster than playing with the keyboard controller to hit reset. That's all from memory so it may be a little incorrect, but the theory is sound. It may have been only a double fault, but either way that method was MUCH faster than resetting through the keyboard controller. Andrew - To Unsubscribe: send mail to majordomo(a)freiburg.linux.de with "unsubscribe openbios" in the body of the message

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mailing list errors
by Stefan Reinauer 14 Jul '99

14 Jul '99

Hi,.. I am sorry, but the mailing list seems to have some weird problems since our university just thought off some new games to make mail undeliverable. You might get one or more mails "Relaying denied." when sending to the mailing list :-( I hope it is fixed withing the next two days.. Best regards, Stefan -- Can you afford *not* to use linux? - To Unsubscribe: send mail to majordomo(a)freiburg.linux.de with "unsubscribe openbios" in the body of the message

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Re: [OpenBIOS] Why protected mode?
by Timothy J. Massey 08 Jul '99

08 Jul '99

On Thu, 8 Jul 1999 10:39:53 -0500 (CDT), Brian Hurt wrote: >) I don't know of any other free usable 16-bit DOS >compilers out there (I'd rather not use an old, properietary, unsupported >compiler like Borland C for DOS). There are very few. From my longtime experience with the FreeDOS project, we have found that the only other decent alternative is Pacific C. I don't have a link handy, but it's not quite ANSI compatible, and it has some real limitations. Tim Massey - To Unsubscribe: send mail to majordomo(a)freiburg.linux.de with "unsubscribe openbios" in the body of the message

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Why protected mode?
by Brian Hurt 08 Jul '99

08 Jul '99

Sorry about the newbie questions- I still can't get at the FAQ. Pointers to where I can get this document gladly accepted. Or a pointer to the archive of this mailing list. Or the CVS repository for the code. Why is the bios going into protected mode? This would seem to make life difficult to load an OS. Is there a game plan for dealing with this that I'm not seeing? The problem is that the linux load sequence is 16-bit code, which loads the idt and gdt and then performs dozens of more instructions before going into protected mode. The solutions I see are: 1) Don't go into protected mode. So long as addresses stay below 1 meg, this shouldn't be a problem (PCI/AGP configuration is the only reason I know of why we may need to go above 1M). 2) Go into protected mode for initial configuration, then exit it to load the boot code (note that the BIOS service routines would have to run in real mode in this case). 3) Stay in protected mode, run the OS loader in V86 mode, and "cleverly" handle the protection fauls (probably by "emulating" them- on the lidt/gidt instructions we save off their offsets, and on the lmsw instruction doing all three- lidt/gidt/lmsw). 4) Same as above, but instead of emulating the instructions, we exit from protected mode at that point, and retry the instruction (and hope that no one ever tries to use a BIOS service after executing a protected instruction). 5) Beg the OS maintainers to change their code. I dislike this option intensely- while on Linux we could probably do it (by becoming OS maintainers), I doubt Microsoft would listen. Brian - To Unsubscribe: send mail to majordomo(a)freiburg.linux.de with "unsubscribe openbios" in the body of the message

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