The thing that make the Fulcrum stuff so cool at the time was the chips being asynchronous, which is very very strange. Fulcurm had to built their own tools to validate the layout etc. Amazingly complex. Most people do not realize how amazingly complex this ASIC stuff is and how hard it is to get right without major bugs.
One very interesting bug, but one that did not really matter, was handing 1G at line rate. For those that do not know a bit of a background.
So you have a 10G chip that connects to a PHY chip.
There are 4 x 3.25G lanes to the PHY. Now lets say you want to put a 1G SFP in that port. Well the path uses only one of the 3.25G lanes, not all 4. All the of logic and timing is really built around the packets going over the 4 links.
So anyway, if you ran a test at 100% line rate with a 1G optic there would be drops if your packet size was not divisible by 4. The stand packets sizes that are commonly used for RFC2544 testing are 64,128,256,512,1024,1280,1518. So all the sizes work expect for 1518. You could do 10G at line rate @ 1518 packet size but not 1G! It is very important for everyone to understand that this only matters in lab testing and has ZERO impact in a real world environment. If you changed the IFG on the link it would run at line rate.
One very interesting bug, but one that did not really matter, was handing 1G at line rate. For those that do not know a bit of a background.
So you have a 10G chip that connects to a PHY chip.
http://en.wikipedia.org/wiki/SerDes
There are 4 x 3.25G lanes to the PHY. Now lets say you want to put a 1G SFP in that port. Well the path uses only one of the 3.25G lanes, not all 4. All the of logic and timing is really built around the packets going over the 4 links.
So anyway, if you ran a test at 100% line rate with a 1G optic there would be drops if your packet size was not divisible by 4. The stand packets sizes that are commonly used for RFC2544 testing are 64,128,256,512,1024,1280,1518. So all the sizes work expect for 1518. You could do 10G at line rate @ 1518 packet size but not 1G! It is very important for everyone to understand that this only matters in lab testing and has ZERO impact in a real world environment. If you changed the IFG on the link it would run at line rate.
http://en.wikipedia.org/wiki/Interpacket_gap
The Fulcurm chips were amazing. I very much enjoyed using them.