[f-cpu] Re:

[whygee@club-internet.fr]

hello,

>De: justin anderson <justina@cat.co.za>
>Hi guys,
>	from what I have seen you are wanting to produce an ASIC.
not exactly. The goal is to design and make freely available a CPU
architecture and one or several implementations in VHDL (and other
langages if people want to translate VHDL...).
It is out of our scope and possibility to "produce an ASIC".

However, there are some means/way to get some silicium fabbed
in low quantity or for prototyping :-)

> Just wondering what would be involved if a person
> were to use a large high speed FPGA as a processor. 
hmmm let me guess ... a large power supply ? 
:-)
no, i'm just kidding.

> Large devices are in the order of 10M gate running at 400MHz, from Xilinx.
The F-CPU multiplier already runs above 100MHz, IIRC.

>  This allows you to design a computer which can be changed.
it depends on what you want and what you can afford.
If your application domain requires a lot of customization,
you can probably make the effort to buy all the toolchain
and the expensive devices (i could probably buy my weight
in chocolate for this price). However, if you're less concerned
by customization, you can prefer to buy a new version every
3 or 6 months (just like you change your Linux Kernel).

>  The speed tracks fpga technology and as larger faster
> fpga's are release so to will the processor grow.
However, do NOT forget some inherent laws of microelectronics;
particularly about signal routing !
When your IC is larger, you can get higher frequencies but you
are also limited by the decreasing I/O pad vs gates ratio.
THis means that your system will starve. "size is not everything" !

Another detail is that today, a large part of a CPU is used by cache
but FPGA do not have large enough cache blocks. you will always lag
by 5x or 10x compared to state-of-the-art commercial CPUs.

>  With some of these fpga's sections can be reprogrammed in
>operation.  This allows for possible software acceleration tailored to a
>specific application eq. graphics or sound processing.

maybe, but it is out of the scope of this project.
If you have particular suggestions, we can discuss about it.

>cheers Justin
read you soon, YG

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