The FCAT tools
You may recall that we first talked to Nvidia's Tom Petersen about frame latencies and multi-GPU micro-stuttering right when we first started looking at these things. To our surprise, Petersen had obviously been working on these matters before we spoke, because he very quickly produced a fairly robust presentation related to micro-stuttering and Fraps captures. That was about a year and a half ago. Turns out Peteresen and his team have been working on FCAT tools for about two years. We've had a few hints along the way that something along these lines was in the works, and that some tools might be presented to the press when the time was right. A couple of weeks ago, Petersen and another Nvidia rep visited Damage Labs to help us get up and running with a frame capture setup and the FCAT suite of tools.
This setup requires a few bits of very specific hardware and a fairly capable host PC.
Pictured above is a Datapath VisionDVI-DL video capture card, which is capable of capturing uncompressed digital video over a dual-link DVI link at very high resolutions and refresh rates. For our purposes, it's able to collect each and every frame of a video sequence at resolutions up to 2560x1440 at a refresh rate of 60 Hz—enough to stress a high-end GPU config running the latest games. (2560x1600 doesn't seem to work, for what it's worth.) During such a capture, the card is streaming data at a rate of 422 MB/s, which is... considerable.
I can't say the setup process for this card is easy. The thing didn't want to work at all with our Intel X79 motherboard (although I'd rather not work with an Intel X79 motherboard myself, I must admit). We eventually got it going with an MSI Z77 board, but we had to disable a number of extra system devices, like USB 3.0 and auxiliary storage controllers, in order to get it working consistently.
The video output from the gaming system being tested connects to this Gefen dual-link DVI splitter, which feeds outputs to both the monitor and the DVI capture card. Nvidia told us its cards could avoid using a splitter by working in clone mode. However, clone mode is not always possible on Radeons in conjunction with CrossFire, so Nvidia chose to include a splitter in its FCAT config for reviewers.
We were advised that we'd need a storage subsystem capable of fast and truly sustained transfer rates, so we turned to the folks at Corsair, who kindly supplied four Neutron SSDs for our capture rig. At Nvidia's suggestion, we attached them to an Intel storage controller and put them into a RAID 0 config. If you like round numbers, this array is almost a terabyte of storage capable of writing at almost one gigabyte per second.
Which ain't bad. In fact, it's shockingly good and consistent; we virtually never saw dropped frames once our capture setup was configured properly. I suspect this RAID could easily go faster if Intel storage controllers had more than two 6Gbps SATA ports available.
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