Re: [Oslib-devel] how to...

[Luca A. <luc...@em...>]

Hi Juras,

[...]

> Do you mean something like this:
> 
> void mytimerhandler()
> {
>  if (vm86task)
>   {
>    // jump to vm86 timer handler through real mode interrupt table
>    // by setting VM86 task's CS:IP pointer, pushing flags etc.
>    return;
>   }
> 
>   // switch to the next task in the scheduler's queue and
>   // handle timer interrupt for 32-bit OS needs
> 
> }
Yes, more or less... I don't know if the "jump to vm86 timer handler" part
is needed, hence I'd do something in the line of:

void mytimerhandler()
{
  if (<task is vm86>) {
    return;
  }

  <call scheduler and do your usual stuff>
}
 
> I think this will HALT the task-switching mechanism while a VM86-task is not
> yet finished and paralyze the system...
As I said, I would "play safe", and consider the vm86 task as nonpreemptable (or as the
highest priority task in a fixed priority scheduler).
This will surely have some effects on system latencies, but I don't think it will paralyze the
system. After verifying that this work, you can try more aggressive approaches, like
scheduling the vm86 task.

> But maybe I should handle an interrupt twice, i.e. emulate interrupt for VM86
> task (pushing flags, setting CS:IP...) and handle the interrupt as usual for OS
> needs?
I don't think this is needed. 

					Luca
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