02-20-2009 03:17 AM
I need to select between two different external reference clocks for the GTP Rocket IO tile, 156.25MHz and 125MHz. What would be the best/cleanest way to do this? Both reference clocks would be coming from external differential oscillators (thus very low jitter) and I would select which would feed the Rocket IO reference tile. Can I just use the simple global clock mux selector or do I need to do something more fancy, such as two DCMs and a PLL (to clean up jitter)?
02-20-2009 09:40 AM
I have done this exact thing, but I used an external 2:1 LVDS multiplexer to allow
use of the GTP direct reference clock input. I would not suggest using fabric
clocks as a GTP reference.
02-23-2009 12:04 AM
consider ICS85401, which is a clock mux that is used for GTPs' ref clocks on ML50x demo board.
02-25-2009 06:05 AM - edited 02-25-2009 08:01 AM
"consider ICS85401, which is a clock mux that is used for GTPs' ref clocks on ML50x demo board."
Are they die ports J20 and J21 for ML505?
03-05-2009 01:55 AM
Thanks for the suggestions.
A related question.....I also need to switch between a 20/16 bit and 10/8 bit interface on the Rocket I/O. Can I do this using the DRP configuration port? Otherwise I have to add some staging logic to take a 16 bit 1x clock rate interface and change it to an 8 bit 2x clock rate interface. I'd rather not do that.