Re: Smart/Dumb box again... (CPU timing)

Alan,

Not sure if I'll actually work on implementing this or not, but I'd
like to keep time in terms of clock cycles on the CPU - similarly to
how some PICs have a timing register incremented each cycle.

The way TurboCNC handles interpolation is to check *each* axis at
some regular interval (around 30kHz) and update if needed. For a
smooth step rate, a much shorter update than the step rate is needed.

I'd like to get away from that model and have a "task stack"
instead, with the time until the most urgent task stored at the top of
the stack. Really, since all the machine does is flip pins on, off,
or check the state of a pin, it shouldn't be all that tricky. So with
the time to wait until the next task, stored in ECX say, then here's a
cheezy CPU delay:

Tick: SUB ECX, $04 (1)
JNZ Tick (3/1)

That sucks, since it can only resolve to 1/4 the clock frequency.
So making it a bit more clever by shifting down the odd bits:

.80486
:: Enter with ECX as number of clock cycles to wait ::

Shift: MOV EDX,ECX (1)
AND EDX,$03 (1)
JZ Timer1 (3/1)
SUB ECX,$07 (1)
JMP Shift (3)
Timer1: SUB ECX,$08 (1)
NOP (1)
NOP (1)
Timer: SUB ECX,$04 (1)
JNZ Timer (3/1)

::Code to be executed::

So as long as the delay is at least 32 cycles long and less than
2^32, the step action should happen regularly within a clock cycle.
(No interrupts!)

On my 486-66, that works out to delays of around a minute to 0.5uS
resolved to 15nS. With steppers, the pulse timing has to be pretty
exact, but the times "in between" are fairly long by comparison - well
long enough to calculate when to flip the pin again.

I figure with some logic on top to run and check the COM port
for data when there's time to spare (next event >1000 clocks or so)
and so on, it ought to be pretty workable.

Dave Kowalczyk
Ames IA

--- In CAD_CAM_EDM_DRO@y..., Alan Marconett KM6VV <KM6VV@a...> wrote:
{snip}
>
> Work continues. Accurate timing is quite important; made easier by
> having "complete control" of the box. Ideas?
>
> Alan KM6VV