[sdiy] Sound synthesis with microcontrollers

[Scott Gravenhorst]

Also when comparing uC devices, something often overlooked is
the efficiency of the instructions and methodology of
arriving at a result.  

For example, 2 devices, say at 10MHz (A) and 20MHz (B). 
Which is faster?  Given only that data, the easy guess is
"B".  But is it really?

If A moves data in 2 cycles and B in 8 cycles, which is faster?  

One needs to look at the efficiency of the instructions you
will be using, or at least those most commonly used.

In my work with uC devices, I'll write the same program using
both machine languages, apply cycles per instruction, do the
sum, calculate the *real* time to execute.  Then you get a
real idea of which is truly faster and for your application.  

Eg: Motorola and Intel have very different approaches, at
least up to the 68000 (maybe I'm thinking 6800).  Motorola
uses what they call a "random logic" approach, which is
essentially a complex logic tree.  Apply an input and a
moment later (given gate propogation delay) an answer appears
on output terminals.  Intel uses a "control store" method,
where by data is cycled via data paths through an ALU and
other logic elements repeatedly giving rise to the same
result, but using radically different numbers of CPU cycles.
 Where an add instruction might require only 2 cycles in the
Motorola chip, it could require 8 or 10 in the Intel.  And
among control store devices, a larger control store and data
path structure usually means fewer cycles.  This is why cheap
often equals slow.

So megahertz, by itself, is quite meaningless.

jbv <jbv.silences at club-internet.fr> wrote:
>Hi list,
>
>Regarding all those uC you guys mention :
>are they 8 or 16 bits ?
>
>And when you say "they're very fast", at
>which frequency clock do they actually run ?
>
>Best,
>JB
>
>

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