Re: rewriting CSP processes

["B.M. Cook" <b.m.cook@xxxxxxxxxxxxxx>]

John, et al.

> I've a CSP question. The words around the mathematics
> talk about "events" being instantaneous transactions that
> are handshaken (both the Roscoe and Schneider books 
> use those terms).  In real life, that's not possible.  Handshaking 
> protocols don't execute in zero time, and signals don't
> propagate instantly.  Is there anything in the CSP literature
> that deals with this problem?
>...

There are some (common) situations in which things appear as required.
Clocked logic only changes state on clock edges, it is not possible to
distinguish time intervals less than a clock cycle time. Here it is easy for
each synchronizing process to assert a signal to indicate its readiness, and
for a logical AND of all the participants to indicate (in the clock cycle
that it happens) completion. *Effectively* we have "instantaneous"
transactions. With real delays from propagating signals we increase the
clock period (slow the system down) until the above holds. (Aside, the
maximum clock rate for things like processors is determined by propagation
delays across the silicon. A proposed solution is to divide the chip into
local clock domains with message passing between them - and the world
re-invents transputers!)

It is *very* much harder to synchronize logic with multiple clocks and other
realities.

There is also Adrian's timed CSP.

        Barry.

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| Barry M Cook, BSc, PhD, CEng, MBCS                                         |
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