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Technology Stocks : 3DFX -- Ignore unavailable to you. Want to Upgrade?

To: Michael Linov who wrote (8083)	10/9/1998 5:01:00 PM
From: Michael Linov	Respond to of 16960

Interesting update from Creative Labs on their V2 SLI Driver. (This note apparently applies to ALL SLI configs, not sure if X24) Apparently, 3dfx subtracts 5 Mhz off your clock speed when you run SLI for safety. This message is for Voodoo2 owners who have an SLI rig and who have been trying out our Release Candidate drivers. Almost immediately after we posted the RC on our web site, several astute customers with two-card SLI setups noticed a peculiar thing: the clock rate in the registry was 3MHz higher than the value set by the slider. For example, if they set their slider to 94MHz, the clock rate was 97MHz. This was first thought to be a bug by several of you, until I jumped in and mentioned that it was deliberate. At the time I wasn't yet ready to give an explanation, as I needed to touch base with 3Dfx on a few things. This got the rumors going. Was it there so we could generate higher benchmark scores? Did it have to do with the two-headed monkey on the 3Dfx site? Crop circles? It's actually none of those. According to 3Dfx, timing in SLI mode is very tricky. Well, actually, timing is tricky with any high-performance product of the calibre of the Voodoo2, but it just gets more difficult when synchronizing two cards with a cable. When 3Dfx began testing, they had failures in SLI mode at normal clock speeds with a very low number of cards (according to 3Dfx this was probably lower than 1%, but this was high enough for them to be concerned). Given that fact as well as the possibility of vendors producing slightly out-of-spec cards or even out-of-spec SLI cables, they decided to improve reliability by reducing the clock speed by 5MHz when the Voodoo2 runs in SLI mode. For example, say you have your clock slider set to 95MHz. If the 3Dfx driver detects that you're running in SLI mode, it subtracts 5MHz, netting a clock speed of 90MHz. Again, this is done by 3Dfx to ensure maximum compatibility in SLI mode, where the capacity for something to fail is greater than with single boards. This subtraction is done at the very "back end," and in the above example, the clock speed in the registry is shown as 95MHz. By the way, here I'd like to point out that we discovered this entirely by accident one day when one of our developers hung a Voodoo2 card on a debugger. As far as I can tell, no other vendor has caught this, and no other vendor has modified their software to accomodate for this. The secret's definitely out now, though! (Hi Bob, William and Danny! You each owe me a beer. :-) ) Now, we know that we make high-quality gear (I'm not implying that other vendors don't; simply that we know we DO), and our hunch is that the vast majority of our customers will have no problem running their SLI rigs at the rated speed. We think this 5MHz safety buffer isn't necessary for most of our customers. We'd prefer a clock slider that accurately represents the actual speed at which the cards are running, so we decided to add that 5MHz back when running in SLI mode. However, shortly before releasing the RC, we thought we'd start by being a bit cautious, so we added only 3MHz rather than the full 5MHz. For SLI users, this means... With third-party sliders and owners of other vendors' cards: - You set the slider to 96MHz - 96MHz is written to the registry - 3Dfx reduces 5MHz to ensure maximum compatibility - Net clock speed is 91MHz (95 - 5) With Creative's RC: - You set the slider to 96MHz - Our control panel adds 3MHz to the value entered into the registry - 3Dfx reduces 5MHz to ensure maximum compatibility - Net clock speed is 94MHz (96 + 3 - 5) Note, of course, that this does not increase the maximum speed at which any given SLI rig will run. It simply makes the clock slider more accurate. If you use a third-party slider, setting that slider to 99MHz or setting our slider to 96MHz will accomplish the same thing. Only our slider will be closer to the actual board speed of 94MHz. It's kind of like using a bathroom scale that you know is inaccurate: you can go on mentally subtracting 14 pounds to get your actual weight each time you step on it, or you can just fix the scale. :-) I've already been asked why we acccomplished this via "padding" the registry rather than simply removing the code from the 3Dfx driver which subtracts 5MHz when in SLI mode. Long-time Voodoo2 fans will remember that the software at this level is largely off-limits to vendors. So, where do we go from here? We'll probably do one of three things: - Leave the SLI offset at +3MHz. - Go ahead and increase our SLI offset to +5MHz, so that our clock slider represents the exact speed at which the SLI rig is running. - Add an "SLI Compatibility Mode" check-box which enables or disables this feature. Comments from RC testers are welcome. -- Dylan Rhodes: Product Marketing Manager, Graphics and Video Creative Labs, Inc. Content on this server is copyrighted by Creative Labs. Please use creativehelp.com for tech support questions