rokicki@polya.Stanford.EDU (Tomas G. Rokicki) (08/30/88)
Of course for this particular application there is an easy way.
He's searching for Golumb rulers, and he wants to write out the
results every once in a while, say every ten minutes. So you
put a statement in your main loop
{ static long countdown = BIGCONST ;
if (--countdown <= 0) {
writestate() ;
countdown = BIGCONST ;
}
}
Tune BIGCONST so updates occur every ten minutes or so. This
way you don't have to worry about semaphores, timer devices,
tasks, processes, or anything. Of course, it's not a general
solution by any means, but there you have it.
The more general solution is to spawn a task that talks turkey
with the timer device. When it gets a timer message, it sets
a global flag. The inner loop checks that global flag on every
iteration, and if the flag is set, writes out the data and
resets the flag.
By the way, checking such a flag or counter is such a fast
operation that it shouldn't affect the speed of your program at
all. It doesn't need to be part of the innermost loop, just
somewhere that is guaranteed to be seen more frequently than
your update requests. If necessary, unroll a loop and only
check once or twice. The flag testing alternative is two
instructions:
tst _checkpoint(a4)
beq normalstuff
jsr _writestate
normalstuff:
(Two instructions, that is, executed inside the inner loop.)
BTW (big thrashing women), for mandlebrot type stuff, only check
after every point, folks, not every time around the z^2+c, obviously.
TTFN (two thrashing female nymphomaniacs) -tom