Idle is a masterclass example why DOS is NOT an operating system.
In a real operating system, there would be ONE method to tell the OS
that "I am currently out of work", not a dozen possibilities to do that.
> Int 28 is vaguely similar, it is the DOS idle interrupt
> called by DOS itself, to give TSR hooking it a chance
> to do stuff while DOS is waiting for keyboard input.
To support mainly PRINT.
> To return to the multitasking topic: In protected mode,
> you cannot just invoke HLT. Your protected mode host
> will get notified that you tried and for example EMM386
> (which often is your protected mode host if no Win3 runs)
> might proceed to do an actual HLT - or just do nothing.
Exactly. And the protected mode hosts responsibility to behave accordingly.
There are a couple of other instructions that don't do what you
think when executed from a real mode client in protected mode
(CLI, STI, POPF, RDTSC, and more)
> Of course you could always try SEVERAL of those methods,
nope
> but that will take CPU itself
Who cares? we have nothing to do anyway!
>>> if (!no_multiplex_int) {
>>> r.w.ax = 0x1680;
>>> intr(0x2f, &r);
>>> no_multiplex_int = r.h.al;
>>> }
>>> else {
>>> cpu_hlt();
>>> }
I'd recommend Bernd's method. It's the best we have.
Tom
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