Date: Tue, 10 Jan 1995 00:04:21 +1100 From: Bruce Evans <bde@zeta.org.au> To: jaitken@csugrad.cs.vt.edu, wollman@halloran-eldar.lcs.mit.edu Cc: hackers@FreeBSD.org, root@io.cts.com Subject: Re: Machine state after reboot? Message-ID: <199501091304.AAA14221@godzilla.zeta.org.au>
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>Quite a lot. The BIOS traps C-A-D and then sends a signal to the >keyboard controller, which uses a spare line on one of its I/O ports >to pull down the hardware reset line, which (depending on the design >of the system) may or may not get propagated to the ISA bus reset >line. Pushing the power button actually kills the power to The standard keyboard reset never resets the ISA bus. It was originally a kludge for switching 80286's back to real mode. Some software depends on switching modes without losing much of the software state, let alone the hardware state, so the behaviour of only resetting the cpu has to be preserved for compatibility. >were, the CPU triple-faults and resets itself. This does not perform >a reset of any of the hardware in the machine, which doing it Actually the cpu triple-faults and shuts down. "Compatible" motherboards detect the shutdown and turn it into a reset. >``properly'' might or might not do. Unfortunately, the keyboard >controller hack doesn't work on all machines (although it is supposed >to), and so WFJ (yes, this is his doing) went this route instead. I think it does work on all machines, but it is tricky to program. Bruce
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