Re: Using "delay until" in real-time

[Brian Orpin <abuse@borpin.co.uk>]

On Tue, 12 Dec 2000 16:27:31 GMT, Ted Dennison <dennison@telepath.com>
wrote:

>On our system ticks come
>at 240Hz, so that means that once every 52 seconds the executive
>scheduler waits about 20ms instead of 16.6(6-repeating)ms. Of course
>this wreaks havoc in our hard-realtime system.

What we do for varying iteration rates is have a scheduler that runs on
every tick.  This then decides what to fire off and initiates the
appropriate tasks.  We do not use the real time clock but rely on
external interrupts and a counter reset at the lowest rate.  We do a 'mod
= 0' to decide what needs to run.  Doing this we have 5 'working' tasks
running at different rates.  Of course your incoming interrupt must be of
an appropriate frequency!

-- 
Brian Orpin    BAE SYSTEMS, Edinburgh
"If you really know C++, there isn't much you can't do with it, though it may 
not always be what you intended!"  Tucker Taft 1998