Re: [f-cpu] Running long things (was: Re: Yet Another Upload)

[Michael Riepe <michael@stud.uni-hannover.de>]

On Thu, Apr 24, 2003 at 11:09:56AM +0200, devik wrote:
> By the way, I never looked at simulators, why are some "slow"
> and some fast ?
> I'd expect to compile VHDL code to be "executable", map bitvectors
> to cpu registers and run processes.

As with any other language, you can compile or interpret the code, or
compile for a virtual machine (like Simili does).  Vanilla seems to be
an interpreter (very slow), Alliance creates intermediate C code, IIRC.
Some tools may also compile VHDL to machine code internally and execute
the result directly from memory.

> Maybe is there difference that better simulator knows how to
> "collapse" several vhdl statements to be run by fewer cpu insns ?
> 
> Or are there problems with multivalued types (std_[u]logic) ?

That's just a matter of clever encoding, I guess.  Although it will
probably always be slower than binary logic (bit and bit_vector).
You can put at most 8 std_ulogic values into a 32-bit word...

-- 
 Michael "Tired" Riepe <Michael.Riepe@stud.uni-hannover.de>
 "All I wanna do is have a little fun before I die"
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