Imagination Technologies / STMicro PowerVR Series 3: KYRO

The Future of Tile Rendering

So why doesn't everyone use tile based rendering? Since it is not the conventional 3D that we've had for years, it requires a complete redesign. Imagination Technology has already been through these growing pains and is thus ahead of the game. Will everything eventually transition to tile rendering? We wouldn't be surprised, but it is very hard to say for certain.

Consider for a moment that by the end of this year, we'll already be pushing 200 MHz DDR (400 MHz effective) memory on a 128-bit bus just for graphics. We're approaching the speed limits of current memory technologies and the bus can't be widened much more. So what's the solution? Rambus would like you to believe it's RDRAM, but a more efficient rendering scheme seems to make more sense.

So just how much bandwidth does tile based rendering save and how much does it need. If you ask Imagination Technologies, a traditional 3D accelerator requires 5.3GB/s of memory bandwidth for 1024x768x32 at 60 fps, which just happens to be exactly what the GeForce 2 GTS and Voodoo5 5500 both have available to them. Mean while, the KYRO under the same conditions requires just under 2GB/s, which also happens to be exactly what it has available to it. The GeForce 2 GTS is able to hit 80 fps in Quake III Arena under those conditions, so obviously these numbers are skewed a bit, most likely in favor of KYRO. For the full details of these calculations, visit http://kyro.st.com and read the white paper on Tile Based Rendering. Stepping up to 1600x1200x32, traditional accelerators need 13 GB/s of bandwidth under the same conditions, while PowerVR tile rendering would need just under 4GB/s. Interestingly, if these numbers are accurate, DDR memory at 166 MHz already has more than enough bandwidth to handle 1600x1200x32, whereas there is virtually nothing on the horizon that can provide 13GB/s of bandwidth.

The one possibility is embedded DRAM, or eDRAM for short, which is just DRAM integrated onto the graphics core. Bitboys is currently the biggest proponent of this solution, but we've seen nothing from them beyond press releases and hype for quite a while now. Their press releases claim 9MB of eDRAM running on a 512-bit internal bus for a total of 9.6GB/s of memory bandwidth. Still not quite up to the 13GB/s number from Imagination Technologies, but certainly impressive nonetheless. If you do the math, that comes out to either a 600 MHz clock or DDR style transfers at 300 MHz. However, eDRAM will add quite a few transistors to any graphics core and would probably not be a viable solution for something already as complex as the GeForce 2 GTS for example.

It seems that 3dfx believes in tile rendering as evidenced by their recent aquisition of Gigapixel. Gigapixel had been touting their GP-1 core as the first gigapixel graphics technology that also had the ability to perform free FSAA. The GP-1 was also a tile renderer, but has yet to released to be turned into an actual product. Note that even though Gigapixel claimed they have the ability to do free FSAA with their architcecture, the KYRO does not have this ability. Imagination Technologies was definitely the first with an actual product available in the consumer market that incorporated tile based rendering.

If STMicro can move the part to 0.18 micron technology and crank up the clock speed, they have the potential to dominate the market. Imagine a quad pixel pipeline running at 200 MHz and assume an overdraw of 4 for future games - that's 3.2 gigapixels/s of fillrate. A clock speed of 200 MHz on a 0.18 micron process is not completely unreasonable, as evidenced by NVIDIA's much larger GeForce 2 GTS attaining those speeds. Realize that the previous numbers are purely hypothetical. What are sources have told us is that STMicro and Imagination Technologies have an agressive road map that includes eventually adding the Series 3 to motherboards and eventually a T&L product for Series 4. Rumored specs for Series 4 include a 0.18 micron process, 166 MHz clock speed, DDR memory, and quad pixel pipelines - possibly by the end of this year, but most likely for early 2001.

Some History

The original PowerVR Series 1, known as the PCX, was a stand alone 3D accelerator that was the first widely distributed product to use tile based rendering. Matrox sold the PCX for a while, under the name M3D, for just $100. It actually featured a unique rendering method, using infinite planes instead of polygons and lacked a z-buffer completely. The infinite plane setup caused all sorts of problems for developers used to working with traditional polygons. PowerVR Series 2, 3, and beyond do not use infinite planes and do not have the problems associated with the Series 1.

Tile rendering's biggest success is probably in Imagination Technologies own PowerVR Series 2 chip, featured on the Neon250 and Sega Dreamcast. However it was the deal with Sega for the Dreamcast that delayed the PowerVR Series 2 debut on the PC platform for almost a year, which in turn allowed the chip to be passed by in terms of performance. A year is a long time in the 3D accelerator business where product cycles have shortened to just 6 months. This is the reason for the low sales numbers and minimal excitement about the Neon250 at the time of launch, although it was fairly popular in Europe relative to the rest of the world.

PowerVR Series 1 and 2 were designed by Imagination Technologies and manufactured by NEC.

This time around, there is no console system to get in the way of the PC launch of the PowerVR Series 3, now known as KYRO. The 250 in the name Neon250 refers to the claimed effective fillrate of the PowerVR Series 2, which is derived from its 125 MHz clock rate and single pixel pipeline with an overdraw estimate of 2. For Series 3, the thought is that games have progressed to a level where an over draw of 3 is more typical. That means that the Neon250 would actually have an effective fillrate of 375 megapixels/s in today's games. However you look at it, the Series 3 is twice as powerful as the Series 2 in terms of raw fillrate, thanks to the additional pixel pipeline, and includes a number of new features.

And how does STMicro fit into all this? They've licensed the Series 3 technology from Imagination Technologies and will be producing and distributing the KYRO. Those of you that have been around the industry for a while and have good memories may remember that STMicro actually manufactured a portion of the RIVA128 chips and helped take the RIVA128 to markets that NVIDIA may never have been able to penetrate. Sounds like a good partnership for both parties.