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Re: [f-cpu] Late answer



Yann Guidon wrote:
> hi all !
> 
> Ben Franchuk wrote:
> 
>>Thomas Lavergne wrote:
>>
>>>In the discution about loadcons, personnaly I agree with Michael Riepe
>>>solution, because it's possibly a bit more difficult to implement in
>>>hardware side (but I'm not sure... ) but it's a lot simpler and more
>>>powerfull in software side.
>>
> being also a SW guy, i am rather suspicious about the "powerfull" thing.
> First, most of the code will be generated by a compiler, so it's a big factor.

Ok, but if we can make work of compiler easier, why not doing it ?

> Second, i am worried about side effect and how they can be "exploited"
> by hand programmers which would learn bad habits.

If we you the ACC trick we don't have more side effect than with your 
loadcons.

> Finally, remember that the instruction must be easily scheduled on
> FC1, FC2, FC3 etc. and nobody has any idea about how they will be
> architectured.

Ok, but I'm not sure your loadcons was more adapted.

> 
>>>And personnaly I think that the design of a cpu is to find a good middle
>>>between software and hardware.
>>
> certainly. This is why an instruction that looks "cool" on one architecture
> can become "unwanted" on another. Look at the x86 saga, with the ENTER/LEAVE
> or the LEA instructions that are ok, then that are not recommended, etc...
> Also remember that F-CPU is based on the RISC principles. Why make the Xbar
> more complex when it yields no speedup ?
> 

We don't make the XBar more complex if we use an ACC

>>Once the documentaion is final, some static programs hand assembled
>>and desk debugged for common but dumb routines, block moves, strings
>>and multiplies/divides using both simple instructions and higher level
>>ones, to get a feel for the machine.
>>Playing with my CPU design right now flags are the bottle neck, and need
>>to be cleaned up.
> 
> flags are a well-known bottleneck, right ?
> 
> the risk with MR's shifting loadcons is that it will become
> a bottleneck on other architectures.

Not more than other approch, and this was the advantage to easisly allow 
loading of any size constant.


-- 
Thomas Lavergne                       "Le vrai rêveur est celui qui rêve
                                        de l'impossible."  (Elsa Triolet)
thomas.lavergne@laposte.net
d-12@laposte.net    ICQ:#137121910     http://assoc.wanadoo.fr/thallium/

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