19 Jul
2001
19 Jul
'01
1:16 a.m.
Number (3)
seems like really bad form, making a circuit that depends on the
processor running at some specific rate. Much better to write code that is
"aware" of the processor speed and compensates for it.
How do you propose measuring the CPU speed? You always need _some_ timing
reference of a known frequency (for example, one way is to see how many
simple loops you can run between mains frequency interrupts, but you then
need to know the mains frequency). And it adds complexity to the system.
For embedded controllers it's very common to write the code for a
particular clock crystal frequency and be done with it. Particularly for
things like bit-banged serial I/O. A number of my listings start with
comments like 'PIC 16C84 processor clocked at 4MHz' or whatever.