From: deering@deering.Eng.Sun.COM (Michael F. Deering) Subject: Re: TECH: Using TI340x0 Date: 9 Apr 1992 02:31:14 GMT Message-ID: Organization: Sun Microsystems, Mt. View, Ca. Re recent posts about the TI34020 and the i860 as silicon engines for VR. To build reasonable performance 3D rendering HW you need lots of 32-bit flops and lots of deep pixel VRAM writing capability, and at the best price per op you can get. The i860 primarrly exceles as 64-bit/32-bit flop engine. While it has some special pixel rendering instructions, they don't go nearly as fast as an inexpensive gate array can drive VRAM. I designed an i860 into Sun's current highest performance graphics machine, the SparcStation 2GT, but only use the i860 for the tasks it is best suited for. About half of the 32-bit floating point is off-loaded to two TIC30's, and all of the pixel pushing is off-loaded to dedicated silicon. While this is a medium end design, this was designed a few years ago, the same trade-offs have now scaled down into inexpensive architectures that people will be doing VR applications on. The i860 as origionally priced was *not* the least $/flop DSP chip, the reason a lot of graphics people used it was that it had the highest flop/single-chip rating, which kept system architectures simple. While Intel as been aggressively bringing the price of the i860 and its follow-ons down, there are a *lot* of other competative choices out there (and I don't mean just SPARC). For pixel pushing, you're choices are more limited. There are only a few chips out on the general market that accelerate Z-buffered shading; every major system vendor has their own propitary chips, because it can make such a *big* performance difference. The TI34020 is an intermediate choice that can make sense in some markets broader than Z-buffered 3D. All other things (like cost) being equal, the faster the graphics, the better the machine will be for VR. Thus the best designs will be the ones that focus on price-performance, using whatever silicon you can get your hands on. I personally do not like using VR systems under 10 frames per second. Combine this with your personal preference for minimum world complexity (triangle count, total area fill), and its easy to see how limited most of today's silicon choices are. Michael Deering Email: Michael.Deering@Eng.Sun.COM Sun Microsystems Phone: (415) 336-3017 Mountain View, CA