Re: [Discuss-gnuradio] SPARTAN FPGA on USRP2

[Matt Ettus]

On 12/07/2009 10:52 PM, yashas nataraj wrote:
> Hi,
>           My research group is in the process of exploring about the
> purchase of  USRP2 which employs SPARTAN-3-2000. In  this regard, I had
> a few queries:
>
> 1. Is there some room leftover on the SPARTAN-3-2000 for USRP
> programming? - Many people whom I contacted were of the opinion that
> there is not much room left.

In the USRP1 (which has an Altera Cyclone) there is not much space left 
unless you take something else out.

In the USRP2 (Spartan 3-2000), there are many multipliers left (about 
30), many logic slices (about 40%), but almost no Block RAMs (maybe 3 or 
4 depending on how you set it up).  You can always remove functionality 
which you are not using, however.

> 2. What are the pros and cons of the ability to program the FPGA?
>                  a. According to Wikipedia (wrt USRP2),
> "Xilinx's free programming tool, ISE WebPACK, is not compatible with the
> FPGA used for USRP. None of Xilinx's tools are open source, and the
> compatible tool (ISE Foundation) is not free of cost, so it is harder to
> compile the USRP2 firmware".
>                1. Is this statement true?

Correct.  The Spartan 3-2000 will only work with the pay versions of 
Xilinx tools, not the free versions.

>                2. If it is true, is there no other alternative to buying
> the Xilinx tool and to what degree is the incompatibility ie does it
> allow basic programming of the FPGA or not?

The only alternatives to buying the tool are:
- Get it for free, which may be possible if you are at a university or 
have a very good relationship with your Xilinx applications engineer
- Find someone else to compile it for you and send you the bit file.

> 3. I would like to get a better idea of how I could program the Spartan
> III FPGA - basic or extensive?  How often would one re-program the FPGA?
> - Again here, people from Xilinx etc were of the opinion that most of
> the programming would be on the gnu-radio and not on the FPGA and very
> rarely is the FPGA touched.

The vast majority of users never need to change the FPGA code.  It is 
only if you want to do something very specialized that you need to 
change it.

You can change the program as many times as you like, since it is stored 
in the SD card, not on the board.

Matt