Victor Yodaiken wrote:
> the disadvantage of one-shot on uniprocessor x86 machines is that
> reprogramming the clock takes 10 microseconds or so.
That is not true, provided you do not want to use 486s, but is due to
the type of implementation of the concept adopted in RTL. In fact I can
prove that with a different implementation, e.g our older variant for
RTL based on 2.0.xx and RTAI for 2.2.xx, it can go down to 2-3 us on ony
PENTIUM and compatible. In that case you can use the CPU clock and have
just to do two "outb-s" to reprogram the 8254 timer chip counter for the
next shot, the oneshot mode being set once for all at timer
installation.
Since with such a solution a single periodic task, toggling a bit on the
parallel port, can run at about 90 Khz on a PPRO 200 while keeping the
PC alive, compare with RTL yourself, I wonder why a similar solution has
not been adopted in RTL for UPs.
If you need a 486 there is no chance for an improvement. I know that
486s are still of interest for many industrial applications, but most of
them can run in periodic mode, for which there is no such a problem.
Believe me the oneshot mode is a true performance killer for 486s.
Ciao, Paolo.
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