Re: DeskNC Windows version

On 19 Apr, CAD_CAM_EDM_DRO@yahoogroups.com wrote:

> I haven't looked into Linux and it's interrupt rates, but the way I would do
> it is reprogram the hardware timer on the system board to a much higher rate
> then add your own interrupt service routine to divide down the faster tick
> rate back to the original rate for routines that depend on it.

Believe it or not, the original IBM programmer's reference for the
IBMPC circa 1981 showed how to do exactly that - even recommending it
as a technique.

> That's the trick we used to do on DOS to get high interrupt rates. Then trap
> INT 08 if memory serves.

I've frequently been lazy and NOT trapped the interrupt, the result
being the time is WAY OFF by the end of the program.

> I'm not sure what the minimum resolution was but it seems like it was around
> .8 us.

Now I'm getting fuzzy, but I think it's 14.318 MHz / 16 for just over a
one uS minimum period.

14.318 also divides nicely to 3.58, the colour burst frequency for NTSC
video, which is why it was used.

Strange, what we're talking about today in terms of timing pulse
limitations comes about as a result of an IBM design decision in
1979/80.

( to make a machine that could display its output on a conventional TV
AND to put that hardware on the motherboard and not on the display
adapter card AND to then use THAT crystal as a reference for most
other timings AND to use off the shelf Intel support chips.)



Alan

--

Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta