[time-nuts] GPS / GNSS front-end board

[Michael Tharp]

On 06/05/2012 03:31 PM, Attila Kinali wrote:
> * The XC6SLX9 is<10USD more expensive than the SLX6. I think the added
>    value of having twice as much "real estate" would justify the additional
>    price.

Some vendors don't even stock the SLX6, including Digi-Key! Agreed 
though, it would be neat if a CPU capable of doing fixes could be fit 
onto the FPGA alongside. Might be impractical though, a DSP would 
probably be more appropriate. Still, from what I can tell a FPGA makes a 
decent PPS-level phase comparator. You can even gang them up with a 
phase-shifted clock to get finer resolution.

> * Connect the enable pin of the OSC1 to a 2-pin header, so it can be
>    disabled with a simple jumper. And put a SMA connector into the path
>    between OSC1 and the LMK03806 (probably not mounted by default) in order
>    to make using an external clock source easier.
>
> I assume that you are running the ADCs in multiplexed mode and the FPGA
> at 128MHz clock?
>
> How about design tools for the FPGA? As far as i can tell, the ISE WebPack
> does not support the Spartan 6 family.

WebPack does support XC6, or at least the mid-range parts and below. I 
have a XC6SLX45 dev board and have no problems generating bitstreams.

-- m. tharp