Arkady V.Belousov wrote:
> Hi!
Thank you for your quick response
[snip]
> /* all of these are in the DOS DS */
> { 0x0, FP_OFF(int0_handler) }, /* zero divide */
[snip]
> for (i = 0x23; i <= 0x3f; i++)
> setvec(i, empty_handler);
[snip]
Excellent!
> Here you may see, which FreeDOS hooks for own handlers and which
> initializes to empty handler (which just IRETs).
I see that interrupt vectors up through 3F are modified.
> M> For example, the timer ticker interrupt at 1Ch (or 08h).
>
> For timer operation DOS uses BIOS.
One can read the timer tick out of the BIOS Data Area, but in order to get
interrupt notification of timer ticks one must hook int 1Ch (or 08h)
It seems to me that FreeDOS must hook into the BIOS ticker interrupt in
order to get notification of ticks. Probably 1Ch ... but that is not
happening in this code ... so that makes me wonder whether or not there is
someplace else in the FreeDOS code that is hooking the timer interrupt.
I will investigate this a little further.
There is also a CMOS timer interrupt at int 70h. Less likely that this is
being used by FreeDOS.
> M> Q: What is the highest numbered interrupt that is used by
> FreeDOS/MS-DOS ?
>
> What mean "uses"? You mean, through which presents own services?
> INT2F.
Sorry I was not clear.
I mean ... What is the highest numbered interrupt vector that is
'modified' by FreeDOS.
The first 1024 bytes of memory are vectors for the 256 interrupts. What is
the highest byte that is modified by FreeDOS.
>From the code above, it looks like the vector for 3F ... or the first 256
bytes of memory are modified.
Your response was very helpful ... Thank you!
Miguel
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