Hi Alexander. I took a look at the schematic last night. Protel is hard for me to read, probably because I'm not used to it. Overall, the board looks very nice. I have a couple of questions/comments:
1) Is there a particular reason why there's an external SRAM on the board? I notice that there is one on the Ettus N210 board as well, but do guys have a particular purpose in mind for it? The Spartan-6 FPGA has ample on-board Block RAM resources. If it's not strictly necessary, it would remove an ~$10 part from the BOM.
2) Maybe it was just because it was really late, but I couldn't figure out what was happening to the 1 PPS GPS timing pulse. How are you planning to use GPS information to discipline the 26 MHz oscillator?
3) One general recommendation: add lots of test points, particularly around the DC power sources, clock signals, and digital signals of interest going to and from the FPGA. Probing BGAs is a pain without them. Also, strategically placed ground test posts that you can use to clip on a scope probe ground connection will make debugging much easier.
4) 6.5 V is kind of a weird voltage. I'd be inclined to go with a 12V connection to an external power source, which would enable the system to be powered off a car battery, but this point is a matter of opinion more than anything else.
-Robin
On Tue, Oct 4, 2011 at 5:45 PM, Alexander Chemeris
<alexander.chemeris@gmail.com> wrote:
Hi all,
Attached is a new version of our schematics and PCB layout (note, they
may differ a bit with schematics being more recent).
Btw, I found diffpdf tool very useful for schematics comparison:
http://www.qtrac.eu/diffpdf.html
It nicely highlights changes, so you don't miss something.
Our current plan for hardware prototyping is like this:
1. Most important parts of PCB layout should be done by the end of this week
2. Then we have 1 week (maximum!) to do any small changes to layout we
may want and fix bugs we (hopefully) find.
3. Then 1 week for the final layout polishing, adding labels, etc.
4. Final ACK for the layout and we push it to the fab for printing.
Manufacturing and delivery to Moscow will take 2-3 weeks.
5. 1 week for assembly
This is about 5-7 weeks and then we will have a lot of fun with
hardware and software debug.
Robin, do you want to get an assembled board to participate in the
hardware debug session? :)
Btw, could you get a quote for the FPGA from Xilinx for 100pcs?
--
Regards,
Alexander Chemeris.
--
Robin Coxe | Close-Haul Communications, Inc. | Boston, MA
+1-617-470-8825