🚀 go-pugleaf

In article <DE3Dnq.9C2@ssbunews.ih.att.com>,
Al Varney <varney@ihgp1.ih.att.com> wrote:
> In article <id.T8WM1.5V2@nmti.com>, Peter da Silva <peter@nmti.com> wrote:
> >In article <41irqv$t83@usenet.ucs.indiana.edu>,
> >scott goehring <sgoehrin@copper.ucs.indiana.edu> wrote:
> >> time spent servicing _any_ interrupt is time that can't be used for
> >> computation.  it may not seem like much, but in a time-critical
> >> (i.e. real time) application, it can be.

> >Real time operating systems, however, are almost all preemptive. The only
> >ones that aren't are those tiny real-time executives that run in toaster
> >ovens and the like, where the job is simple enough it's practical to do
> >polling.

>    I hate to disagree with a fellow Amiga owner, but there are 'real-time'
> applications that use polling as a means of controlling the admitted
> workload AND a means of maximizing CPU utilization.  Both the 1A ESS(tm)
> and 4ESS(tm) switches primary processors use a non-pre-emptive cooperative
> control, similar to a threaded/message-passing mechanism.  Since each
> 'process' only handles a limited amount of information (1 call, a few
> I/O translations, etc.) before 'yielding', there is no need for pre-emption
> except as an error mechanism to handle run-away software.

OK, if you're doing VERY simple things and can basically complete a
transaction in an interrupt's time, then you can use polling. I know a
guy who ran a multiline BBS that way: at 300 baud, it ran through all 8
ports 30 times a second just in time to get the next character in from the
UART and ship the next character out. Really tricky coding.

This sort of thing is called a "single loop" control system. It really
doesn't *have* an operating system in there at all, just a single application
chomping away for all its worth. A very large "toaster" application. You
don't put a real time operating system or any other kind of operating system
on something like that.
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