Re: F21c
On Sun, 8 Jun 1997, Robert J. Brown wrote:
> >>>>> "Penio" == Penio Penev <penev@venezia.rockefeller.edu> writes:
>
> Penio> On Sat, 7 Jun 1997, Peter Jakacki wrote:
> >> The timer circuit which interrupts the CPU at programmed
> >> intervals is the basic building block of embedded systems, it
> >> is good to see F21 with this timer.
>
> Penio> It is not necessary, though. It you have a tight enough
> Penio> multitasking loop, you can guarantee that a certain code
> Penio> will be executed no later than a certain time it was
> Penio> previously executed. Then you can treat this as a "clock
> Penio> interrupt". Even more, you can think of it as an
> Penio> "interrupt" in general -- you can attach whatever I/O
> Penio> polling code you want there.
>
> Only if the timing is invariant with respect to all possible paths
> thru all subtasks in the loop can you rely on this for sampling analog
> inputs of A to D converters, or strobing outputs to D to A converters.
> If the sampling is not uniform, some very bad distortions can result
> at input, signal processing, or output. The timing must be uniform
> and known. The timer interrupt makes this easy.
Strobing needs a timer, that's true. This is what the analog and/or video
coprocessors are about.
I was refering more to asynchronos (but time-critical) I/O events and
multitasking. For those one does not need a timer.
--
Penio Penev <Penev@pisa.Rockefeller.edu> 1-212-327-7423
