Thursday, January 15, 2015

FPGA cluster updates

Although the "raised floor" design for my FPGA cluster looked cool, it really didn't scale. My entire desk was full, there was very limited room for new hardware, and the boards kept getting dusty. To make matters worse, long wires were needed to connect everything and it was difficult to manage them all.

Original FPGA cluster

I ended up moving forward with the plan I came up with a few months ago and my FPGA cluster is now living on the 19" rack in my living room.

The first step was to laser-cut acrylic frames for each board (or several boards, if they were small enough) that would slide into the card guides.

In the photo below you can see nodes lx9mini0 and lx9mini2 (lx9mini1 was being used for something else at the time so I put it on another card later on) on a clear 1/16" acrylic sheet cut to standard Eurocard dimensions. The clear faceplate was later replaced with an opaque black one because I think it looks better that way.

Spartan-6 FPGA boards on a 3U blade card

My existing USB hubs weren't well suited to the rackmount form factor so I built a new one. This is a ten-port USB 2.0 hub with two front-panel ports (for keyboard and mouse) and eight back-side ports for internal connections. It consists of three 4-port Cypress hub chips in a tree, plus the associated PMICs. For extra fun I threw on an XC2C128 CPLD with a SPI headers so that I could potentially toggle power to individual ports remotely over SPI, but as of now this functionality isn't being used.

As with my previous hub designs all ports are overcurrent protected. I also added external ESD clamp diodes (RCLAMP0514M) to each data line after an killing a previous hub by zapping it while plugging my phone in to charge.

The port indicator LEDs are off in the idle state, green when a device has enumerated successfully, blinking green when a device is detected but fails to enumerate, and red for an overcurrent fault.

3U x 4HP USB hub blade

I went with my original plan of racking the Atlys boards in one of my empty 1U cases and the AC701 in another. The boards are screwed into standoffs which are attached to the case by cyanoacrylate adhesive.

Nodes atlys0 and atlys1 being installed in a 1U server case. JTAG and Ethernet cables are not yet installed.

I then installed my PDU board, the BeagleBone Black, the USB hub, and all of the smaller FPGA boards I was using for my research in the rack. Since I was moving the second 24-port switch from my desk to the rack I hooked the two together with a short run of multimode fiber. Fiber was overkill for the application but I had SFP ports sitting around unused and I was running out of copper interfaces...

The standard I've decided on for all new designs in the near future is as follows:
  • Boards are to be 100mm tall (3U Eurocard height)
  • Component keepouts along the top and bottom edges as specified by the Eurocard standard for card guides
  • Faceplate mounting holes on the front panel as specified by the Eurocard standard
  • 5V DC center-high power via standard 5.5mm barrel jack on the back edge
  • Network jacks and indicator LEDs on the front edge
  • JTAG, USB, and other I/O on the back edge

My current rack
The current FPGA cluster
Back side of the FPGA cluster midway through rack install. The USB cable coming out the bottom was temporary for testing until I could find a right-angle one.
All of the cards have nice shiny black faceplates except my 4-port switch prototype from a few years ago - the laser cutter on campus was unavailable the day I wanted to get the faceplate made and I never got around to doing it.

I still have quite a bit more gear to rack - several Spartan-6 boards I'm not actively using in my research, a Raspberry Pi, a Parallella, and a large number of PIC MCU development boards of various types. This will fill the current card rack and then some, so I left 3U of empty space below this one for expansion. The Parallella runs hot so I ordered a 1U fan tray which will be installed later today.

The 1U blank above the card rack is there for airflow reasons (the fan will blow upwards and exhaust air needs some space to blow out) but I can still fit stuff that doesn't block airflow. Early next week I'll be replacing it with a 16-port LC-LC patch panel so that I can terminate fiber runs to various devices on the rack (such as the AC701 board, which currently has a 2m run of multimode going around the side of the rack because there's no good way to get fiber from back to front).

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