On 08/04/2011 11:06, V G wrote:
> Hi all,
>
> I'm seriously considering getting myself a Papilio. This question is pure=
ly
> out of curiosity. The $50 version has a Spartan 3E FPGA chip with 250K
> gates.
>
> What can I do with 250K gates? How many 8 bit CPU cores can I fit on ther=
e,
> for example? How about an ARM 32 bit core? How many gates (approximately)=
 do
> these cores take?

A small 8-bit core will be a few tens of K - IIRC, the one I am using=20
currently on a ProASIC3 takes about 20K gates, but depends on the=20
settings (you can select different bus widths, whether to enable certain=20
instructions etc) FPGA cores like Picoblaze and CoreABC(Actel) are=20
designed for size/efficiency so are very simple. To get similar to e.g.=20
16F functionality you need more gates - for example IIRC an (Actel) 8051=20
core with no peripherals takes around 60K gates (again depending on=20
settings, but I remember the smallest setup not quite fitting on a 60K=20
device) but you can use the Keil C compiler for it (as opposed to a=20
small popup screen for assembler for the CoreABC - not sure about the=20
Picoblaze though)
Remember you also need RAM, and somewhere to store your program - on the=20
ProASIC you can store instructions in FPGA registers for the CoreABC and=20
use the onboard RAM, but for the 8051 you need an off chip store. I'm=20
not sure how Xilinx do things (probably very similar) but if you are=20
getting a dev board it will likely be setup so you can try various=20
things out easily.
If you want a good idea of what 250K gates will do, read some of the=20
Xilinx core datasheets (counters, adders, UART, SPI, Picoblaze etc) =20
They should have info on how many gates they take, what speed they can=20
run at and so on.


> What CAN and what CAN'T I do with 250K gates? Should I instead go for the
> 500K gates version? Or look for something else entirely?

250K gates will do plenty, I would go for that (I started with 60K and=20
it was more than enough to learn with)

> The Spartan 3E series seem to be pretty cool (and cheap) chips. I checked
> out other chips on Xilinx's and Altera's site and they seem to have some
> seriously high end stuff on there. Just out of curiosity, how much would =
a
> really high end FPGA cost?
>
> I don't know anything about anything about FPGAs so please go easy on me.=
 I
> just have this feeling that Olin's going to attack me on the type of
> question I'm asking.
>
> MAXIMUM ARMOUR. Crysis (2) anyone?


--=20
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