Monday, November 17, 2014

buying fpga boards and connectors for the SAC interface

I am spending the first half of the week in New Orleans at the SC14 conference and flying on to London from here. My posts will be stretched out more than the normal post-a-day pace I try to maintain, partly because I have little time to work on 1130 matters and in large part because I am separated from the 1130.

A reader of the blog has offered some test and repair equipment to me for just the cost to ship it - a very generous act that came in an email out of the blue. It will arm me with a much stronger logic analyzer capability for when I am debugging hardware, plus a full feature soldering rework station that offers many nice features that at the present I either have cobbled together partially or lack entirely.


The number of input-output lines used on the Storage Access Channel is 77, which exceeds the input-output connections available on most fpga development kits such as my Nexys2 and Nexys3 boards. While I could address this, given the speed potential of fpgas, with serial streams to some hardware that would implement a serial to parallel conversion and latch for outbound signals and the converse for inputs from the 1131, it would be cleaner to have direct connections to all the lines.

I have a Virtex II-pro development system board which has plenty of input-outputs plus great features like SATA disk adapters and SVGA video hardware, but to program this requires a full Xilinx tool license. The free webkit that suffices for the other development boards (for non-commercial use) will not support this board. The cheapest single user license is roughly $3,000 which is a price I am not willing to pay to use this board.

There is a board made by Digilent called the FMC Carrier S6 which provides a high density connector offering 126 input-output pins to a Spartan 6 fpga, at a reasonable price (less than 10% of the cost of the software above). The connector is a surface mount device due to the high density of connections in a small area, which requires a suitable board be built onto which I attach the connector with a reflow oven - these heat solder to a liquid state where surface tension pulls the component and board pads together, both bonding and aligning the part.

I have bought the FMC Carrier S6 board and the high density socket, now I have to design a board to attach this and fan out the connections to the wires from my interface boards. I hope to do the design this week and send it off to manufacturing, which may have it delivered to me about when I come home from my trip. It took a while to be sure I knew which of the 400 pins are connected to each of the signals from the board and which are grounds.

There is an option to buy a Xilinx breakout board which would deliver most of the FMC signals to header pins which I could easily hook to the signals. The board is about $175, but would guarantee I didn't make mistakes with a custom board but that comes at a premium of about $100 over the costs of my own board. I will research this a bit more and think about it overnight.

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