Re: [Discuss-gnuradio] Re: interfacing a DSP array card to USRP2

[Jeff Brower]

Matt-

>> About Vikram's 10/100 mode question, we were wondering if it's a design 
>> flaw; i.e. something wrong from the start in
>> the original opencores.org source, or if it's fixable but hasn't been a high 
>> priority item given USRP2's high data
>> rate requirements.  But then I found this post:
>>
>>    http://www.ruby-forum.com/topic/143084
>>
>> So I guess the former.  If there are any hints you can give on what's wrong, 
>> we can take a look.  Maybe our guys can
>> get it working.
>
>
> Eventually I got completely fed up with the opencores gige core and
> wrote a completely new one from scratch (the simple_gemac).  It only
> does gigabit, though.

Ok.

> One of the main problems with 10/100/1000 in a spartan is that you need
> a large number of clocks and the S3 is constrained.

My understanding is that it takes 3 BUFGs and one DCM for tri-mode (maybe one 
more of each for RGMII support but I
don't see that) and, between this and other USRP2 needs, you ran into the limit 
of 8.  Is that accurate?  Or would
10/100/1000 support would take more than 3...

> If you just want
> 10/100 and can live without gigabit, I would suggest doing that, as it
> will save 1 or 2 clocks.

Ok... maybe we can implement both modes if we're careful.

-Jeff