Question on Reading / interpreting Beaglebone_RevC_Allegro.brd

Hello Beagleboard community,

I have a quick (and silly) question about the beaglebone’s layout. I have opened the beaglebone_RevC_Allegro.brd project in the Allegro Free Physical Viewer and am measuring the lengths of the gpmc connections. I’m getting measures of 2381 as total distance for connector B3 to the processor. My questions are: What unit is allegro reporting in? (is it mils?) and should I be using this value, or the Etch Distance (in this case 1329.60)?

A little background on my purpose: I’ve been designing an fpga add on board for the beagle using a spartan 6. It is similar (and inspired by) the special computing spartan 3 add on board. Unfortunately, I haven’t seen that site updated in some time, so starting back in May ( / June-ish) following some questions posted on this boardabout interfacing with an fpga I started working on my own add in board. I’m not very experienced, and this has been mostly a hobby project, but I feel I’m getting close to having a first prototype made. I’ve had my schematics and layout checked by people at my co-op placement who naturally have torn it apart 3 times now. On my 4th attempt, it’s mostly gotten the “ok, it should probably work” from them, and I am trying to move ahead and send it to manufacturing later this week. At this point I have not done any length matching of the gpmc lines on my board. I knew that that would impact how fast I can run the interface at, but for a first prototype I wasn’t too concerned. Now though, I’m thinking I should take that into consideration so I can go father with my board in the future.

I plan on releasing my entire design once I think it is good enough to not be completely ridiculed by the community :wink:

When I get hardware in hand, I’ll probably be asking around for guidance on the software side of this project, but that is for later and I already have a rough idea of what I need to implement.

Thank you in advance for your time and any thoughts / input you may have.

Have a good one,


It is generally in mils. Etch distance is the length of the etch incluidng all the turns in the traces, so that is a true distance of the etch when looking at it from a potential delay standpoint.