DOS ain't dead

And now: int 0x21 in hw interrupt handler? (Developers)

posted by tom , Germany (West), 19.12.2012, 15:54

> > The InDOS flag is one of a few different checks you need to make to test
> > whether DOS is already doing something or not. The problem is, what do
> you
> > do if it's not safe? Your only option is to wait until it is safe, and
> > that can never happen until you exit the IRQ handler. So, you need to
> have
> > another process to download the data anyway, so you might as well just
> do
> > it that way from the beginning.
>
> If I write the app in a way that it never calls int 0x21 while my IRQ
> handler
> is active, am I safe?
no.
> Are there other interrupts I must also not call?
> BIOS, something else?
dont't call anything.
DOS, BIOS, and basically everything else is NOT reentrant.
doing more then setting a flag at interrupt time is a certain recipe for interesting things to happen ;)
calling XMS to copy some memory (as Japheth suggested) is one of the few exceptions.


> At the moment, I'm not sure I'll do any kind of visual feedback, but I can
> do that by writing directly to the video memory.
actually THIS IS one of the few things safe to do

Complete thread:

• Basics of interrupt chaining? - myrkraverk, 13.12.2012, 19:39
  • Basics of interrupt chaining? - myrkraverk, 13.12.2012, 20:19
  • Basics of interrupt chaining? - Japheth, 13.12.2012, 21:31
    • And now: int 0x21 in hw interrupt handler? - myrkraverk, 14.12.2012, 02:58
      • And now: int 0x21 in hw interrupt handler? - Japheth, 14.12.2012, 06:10
      • And now: int 0x21 in hw interrupt handler? - tom, 14.12.2012, 18:25
      • And now: int 0x21 in hw interrupt handler? - bretjohn, 15.12.2012, 01:29
        • And now: int 0x21 in hw interrupt handler? - myrkraverk, 15.12.2012, 15:52
          • And now: int 0x21 in hw interrupt handler? - bretjohn, 17.12.2012, 18:08
            • And now: int 0x21 in hw interrupt handler? - myrkraverk, 18.12.2012, 20:16
              • And now: int 0x21 in hw interrupt handler? - tom, 19.12.2012, 15:54
  • Basics of interrupt chaining? - bretjohn, 14.12.2012, 19:43