question - how to test DMA on peecees right way?

From: Ward Donald Griffiths III <>
Date: Tue May 12 20:08:51 1998

Tony Duell wrote:
> >
> > Tony Duell wrote:
> > >The first requirement is that you're mad.
> >
> > Now that you're foaming blue at the mouth, you could give the speech
> > about how to use the keyboard interface chip to bring the 286 into
> > real mode and back again... :-)
> Sure, it's not _that_ hard...
> The problem is that the i80286 can go from real mode to protected mode,
> but not back again. At least not without a hardware reset.
> Now, the keyboard controller output port bit 0 will, if pulsed low, reset
> the microprocessor. There's a keyboard controller command for that -
> 0xF1. You send that to output port 0x64. You also need to set the system
> flag (send 0x60, 0x04 to port 0x64 (or maybe 0x60,0x05)), set the CMOS
> shutdown bye (location 0x0F in the RTC) to 0x0A (to mean a user defined
> reset), and set IO_ROM_INIT (far pointer at 0x0040:0067 (offset) and
> 0x0040:0069 (segment) to point to your code. Or at least that's what I
> think you do - it's late and I'm readign the BIOS code as I type...

Yes, Tony, obviously "The first requirement is that you're mad." (We're
not talking _angry_ here, kids! "Mad" in English isn't the same thing
as in American.)
Ward Griffiths
They say that politics makes strange bedfellows.
Of course, the main reason they cuddle up is to screw somebody else.
				Michael Flynn, _Rogue Star_
Received on Tue May 12 1998 - 20:08:51 BST

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