Re: finite state machine/automaton framework?

["Simon 'corecode' Schubert" <corecode@xxxxxxxxxxxx>]

On 03.09.2004, at 19:54, Matthew Dillon wrote:
> :hey,
> :
> :considering that operating systems in general (and dfly in special)
> :have lots of finite state machines in source - most of them hidden as
> :evil if/else constructs of which the authors supposedly never heard
> :about FSM before.
> :Is it a good or bad idea to have a (simple) FSM framework available
> :which can be used by different parts of the operating system? If yes,
> :do such frameworks already exist?
> :
> :Just a thought because of the need to implement a i8254 PIT 
> emulation...
>     Well, I don't think it's really applicable to what the kernel
>     has to do in most cases.  For example, emulating an 8254 with an 
> FSM
>     would basically require emulating the 8254's logic, which would 
> take
>     megabytes through a generic FSM module, even one designed for logic
>     emulation.  But it would only a few kilobytes if you 'faked' it in 
> C
>     (emulated the 8254 at a functional level rather then at a logic
>     level).

I was thinking of a system that generates C code out of a formal 
description. This way the code wouldn't differ much from the hand 
written one, but it would definitely be better to maintain (compare 
yacc).

for example:

state_idle:
  if:
    written_byte & WHATEVER_BITMASK
  newstate:
    state_program_oneshot
  output:
    this_var = that_var;
    run_foo();

etc

cheers
  simon

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