question - how to test DMA on peecees right way?

From: Captain Napalm <spc_at_armigeron.com>
Date: Tue May 12 16:56:31 1998

It was thus said that the Great Tony Duell once stated:
>
> >
> > 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.

  Well, there is at least one way through software, maybe two. Both are
undocumented, but work.

  The first is to use the LOADALL instruction (different format between the
286 and 386. I think Intel finally removed that instruction on the
Pentiums). The second way is to triple fault the CPU (I know that works on
the 386 or higher, not exactly sure about the 286). Both are faster than
the hardware reset method.

  -spc (Now getting a triple fault is a bit tricky ... )
Received on Tue May 12 1998 - 16:56:31 BST