Alliance Semiconductor AT3D review

Alliance Semiconductor AT3D

Logo of Alliance is on many memory chips of the nineties. Their ProMotion line of 2D graphics also did not fail, but were not exactly famous either. The company had one unique aspect among the 3D crowd- they could use their own RAM and even the flash memory for BIOS. Alliance got more attention from gamers when their graphics cores were chosen for Voodoo Rush boards supporting 3D only chipset of 3Dfx. Technical specs says that Alliance chips got a special 64 bit bus for fast communication with Rush. Let me guess, they split the 128 bit bus into two. But what made AT3D more attractive than other (2D only) chips embraced by 3Dfx? They sure feel better than MX, but I am not benchmarking 2D. Alliance promised all-in-one solution for new multimedia age. Alliance focused on 3d, they launched developer program "A+" one year in advance, to have games ready.

The card

Here is a casual AT3D board with RAM capacity maxed out at 4MB. The chip also supported odd sizes of 1.5 and 3 MB. Removing the expansion memory would make the EDO work in single cycle mode rather than interleaved. This particular card has awful signal quality, which should not be blamed on 175 MHz DAC of AT3D. DirectX5 driver 2.072 was used. It sets memory clock 60 MHz and it is reasonable to expect clock of the 350nm chip to be synchronous.

Reality check

AT3D arrived in summer 1997 and Alliance was showing it off as a true second generation 3d accelerator. Any 3d rendering scenario should be performed in one pass. I am of course testing pure AT3D board. Specifications promised a fine piece of 3D accelerator, press announcement and datasheet would make you think you cannot go wrong. Big numbers, triangle setup, free per-pixel perspective correction, all the texture formats and blending operations supported, 128 bit video engine and 128 bit memory bus. And then you fire up the card, play games and everything is broken. Many people often say something in early 3D chip is broken, dissing the likes of Trident 975, Rage or even Riva 128. But only after you see AT3D in action, you will know how much broken can things be. It is not only the monochrome dynamic lighting or stipple patterns used for all but one transparency mode. Even specular highlights are done via stipple mask. All texture formats from palletized up to 8880 are supported. True color textures are full speed and true color buffer is also possible with a small performance penalty. However, at such depth only palletized textures may be blended "properly". And since AT3D does not use system memory there is with 4 MB little hope for true color rendering at higher resolutions. On brighter side, AT3D datasheet mentions proprietary technique of Z-buffering in as little as 8KB off screen memory. Could it mean AT3D is tiling the scene? Frankly, I have no idea, datasheet also mentions Z-buffer compression, but the card does not behave like if it has more memory than others.

Gouraud shading is done full speed and geometry looks perspectively ok. Texturing however, is so warped it turns your accelerated games into chaos barfed all over your display. Perspective correction might have been very well implemented without performance penalty, but somehow at the end all important textures are not adjusted. It reminds me of certain quadrilateral texturing chip trying to render triangles. Such artifacts also prevents closer inspection of Alliances Pseudo Bilinear texture filtering. Let me just say if often exposes problems in the style of Trident 3DImage. Normally such image quality would disqualify the card from benchmarks, but just to get some idea of it's performance I measured few games that were recognizable. Modern art lovers should enjoy the impressive gallery. That is the fun of early 3d accelerators.


I think their aniso filter dropped too many samples at 80°, that mountain is a bit noisy.

This is with last official driver 2072 which Alliance still offers on their web for download. Even if the basics of textured polygons worked properly the AT3D would not get high image quality marks. Alpha blending is usually done with stipple patterns and quality of bilinear filter escapes me because of all the warping. The last thing I can deduce from such awful gallery is per polygon mip-mapping with unstable mip selection.

Results

Performance is not the worst, but it is not impressive either. Usually AT3D fails to deliver on the promise of 30 frames per second at 640x480x16. This board can manage 74 MHz overclock, giving it a healthy 20% boost in 3d performance. I was too disgusted to measure games again, though.


Conclusion

Well, that was fast. Alliance had more plans with this architecture. Still in that summer AT3D+ with support for larger frame buffers and full AGP 1x support should be sampled and some time later AT4D with side-band addressing and 133 MHz AGP support. I take abandonment of those chips as another proof of how broken the design was. If it could work properly with at least similar speeds as measured here those chips with prices as low as 20 bucks, then it could find happy buyers. Alliance also develope own embedded DRAM that should have used together with AT3D and newer graphics. 2MB of on-die memory should have power ED2D (AT3D on PCI) and ED4D (AT3D on AGP), but were canned as well. Alliance did not give up on 3d after this disaster and announced another 128 bit architecture: Paladin. Its promise of single cycle bump-mapping was not fulfilled. In summer of 1998 the company ended all support for graphics technologies and continued business only with memory and embedded electronics. They are still alive today, albeit they moved away from semiconductors.