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An actual IBM-PC could reliably be rebooted using the keyboard controller (as mentioned in the article). The issues come with IBM-PC "compatible" machines. I'm sure commodore would have the same problem if anyone had bothered to clone them.
To be more precise, an IBM PC-AT. It is closely related to the A20 line enable.
Method 6: return to 16-bit mode, call interrupt 0x19 (not if you're on efi). Method 7: return to 16-bit mode, set cs to 0xf000 and jump to 0xfff0. Linux used to use method 6, but it wasn't reliable either. Something tells me returning to 16-bit mode might not be possible for some hardware / driver combinations.
Could you explain in more detail how these trigger a reboot? From writing a 32-bit kernel I understand how the triple fault method is supposed to work, for example, but would love to know a little more about these methods.
Method 6: return to 16-bit mode, call interrupt 0x19 (not if you're on efi). Method 7: return to 16-bit mode, set cs to 0xf000 and jump to 0xfff0. Linux used to use method 6, but it wasn't reliable either. Something tells me returning to 16-bit mode might not be possible for some hardware / driver combinations.
Tried to get an OS on a PC to soft-reboot, failed, because it is not actually possible to return all hardware to the reset state in some cases - they have an initial power-on state and once programmed can never return there unless hard-reset.
And why does the BIOS require hardware in the hard-reset state? Because a BIOS is never tested in a soft-reset scenarios, because Windows doesn't require it. And "if you haven't tried it, it doesn't work".
Earlier quoted context omitted.
To be more precise, an IBM PC-AT. It is closely related to the A20 line enable.
Why should anyone need to mess with the A20 line and the keyboard controller to simply reset a computer?
Earlier quoted context omitted.
Why should anyone need to mess with the A20 line and the keyboard controller to simply reset a computer?
Well, you do need to turn on A20 so it will jump to right address, but if you are in protected mode it should already be on.
Method 6: return to 16-bit mode, call interrupt 0x19 (not if you're on efi). Method 7: return to 16-bit mode, set cs to 0xf000 and jump to 0xfff0. Linux used to use method 6, but it wasn't reliable either. Something tells me returning to 16-bit mode might not be possible for some hardware / driver combinations.
Jumping to the BIOS is not a reliable reboot method either (method 7). Because the BIOS assumes hardware in a hardware-reset state, and the OS left it in some other state. Tried to get an OS on a PC to soft-reboot, failed, because it is not actually possible to return all hardware to the reset state in some cases - they have an initial power-on state and once programmed can never return there unless hard-reset. And w…
I don't know if anyone else remembers, but I think it was either Windows 95 or Windows 98 which, after selecting shut down, the eventual result would be a message that said, "It is now safe to turn off your computer." I remember thinking it was magic when the computer would actually turn itself off at this point. This article provides a good explanation for why that behavior was necessary.
I don't know if anyone else remembers, but I think it was either Windows 95 or Windows 98 which, after selecting shut down, the eventual result would be a message that said, "It is now safe to turn off your computer." I remember thinking it was magic when the computer would actually turn itself off at this point. This article provides a good explanation for why that behavior was necessary.
Power off uses APM or ACPI and is not related.
But since it's not mentioned in the topic, it's going to come up. Personally I use a batch file and SysInternals to shutdown (after forcing bad-behavior apps to exit).
Sounds like you need a SysInternals for Linux??
Earlier quoted context omitted.
Well, you do need to turn on A20 so it will jump to right address, but if you are in protected mode it should already be on.
Isn't that kludgy? I mean, using a keyboard controller (in effect, a second computer) to reset the one you can't?