Re: F21c
>>>>> "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.
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