[haiku-development] Re: Virtual 8086 mode support

Ingo Weinhold <ingo_weinhold@xxxxxx> wrote:
> On 2008-04-19 at 19:28:11 [+0200], Jan Klötzke <
> jan.kloetzke@xxxxxxxxxx>
> wrote:
> > It turned out to be not very difficult in the end. There is a new
> > syscall
> > vm86() which enters virtual 8086 mode for the current thread. The
> > caller
> > passes
> > a structure with all the registers with where the execution should
> > begin in
> > vm86 mode. Whenever a priviliged intruction is executed the vm86()
> > call will
> > return with B_OK or, if a signal is delivered, with B_INTERRUPTED.
> > In any
> > case
> > the passed registers structure will be updated to the values where
> > the vm86
> > mode was left.
> Nice! I wonder, why this is a syscall, though. If the intended use is
> for the
> VESA driver, it won't really help. Or do I miss something?

The VESA driver also has an accelerant. I dunno if one need this
functionality in userland, but you'd need a syscall anyway to offload
that functionality to the driver (just an ioctl(), of course).
Since you want to access low memory (and would need a dedicated kernel
thread to do so in the kernel, otherwise it's mapped by some app), it
might even only be possible to do that in userland ATM.

Bye,
   Axel.

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