SiS530's Onboard VGA
SiS530 Integrated VGA Controller
SiS 530's integrated Super Advanced Graphics Port supports a tightly coupled 64 bit 100MHz host interface to VGA to speed up graphical user interface performance and video playback frame rates. The built-in RAMDAC is programmable to a 24 bit color depth and up to a 230MHz pixel clock and also supports a loadable RAMDAC for gamma correction in true and high color modes. It also has built-in a reference voltage generator, dual-clock generator and monitor sensing circuit and supports DVD hardware acceleration. The integrated VGA controller supports both SDRAM and SGRAM for local framebuffer memory up to 8MB.
- 2D Graphics -
At it's basic level, the
2D graphics engine of the SiS 530 is a 64-bit BitBlt graphics engine. The integrated 3d
VGA controller supports single-cycle read/write and block/write functions of SGRAM.
For enhanced 256-color graphics mode and 32k/64k high-color graphics mode the engine supports the following features
256 raster operations
Enhanced Color expansion
Line-drawing with styled pattern
Built-in 8x16 pattern registers
Built-in 8x8 mask registers
For 16M-color graphics mode, due to different graphics process methods, the engine supports
BitBlt Block Transfer
BitBlt Block Transfer
The integrated VGA controller performs these accelerator functions via the acceleration commands stored in the command queue. The command queue is contained within a FIFO (First-In, First-Out) and ring structure. For example, if an acceleration command is filled in the last stage of the command queue, the next function or command will be stored in the first stage of the command queue. In order to keep the command queue the required length, the controller provides two distinct types of command queue. The first, called the Hardware Queue is built in to the controller itself. The second, called the Turbo Queue, in a process patented by SiS, is located within the off-screen display memory.
- 3D Graphics -
The Turbo Queue architecture is also an important technology aspect of the 3D accelerator and along with the 32-bit floating point format VLIW Triangle Setup Engine, 16kbit Texture Cache and Pipeline Rendering Engine provide the following capabilities for the 3D VGA controller integrated into the SiS 530:
Support for Super AGP
Peak Fill Rate of 40M
A Peak Polygon Rate
of 800K polygons/sec (@ 50pixel Gouraud Shaded, Point-sampled, Linear and Bilinear Texture
Solid, Flat and
Support for Z-test,
Alpha-test and Scissors Clipping
Line Pattern and ROP
Bilinear and Trilinear Texture Filtering
MIP Structure Texture
1/2/4 BPP Palletized
1/2/4/8 BPP Luminance
4/8 BPP Mixed Mode
RGB/ARGB Texture Formats
Blending, Wrapping, Mirror and Clamping
Fogging, Alpha Blending and Primitive Transparency
Using the Turbo Queue architecture speeds up rendering for 3D processing because, since the queue length is virtually infinite, the 3D driver can issue commands without waiting. SiS 530 allocates a portion of the off screen memory as a command queue buffer and when the VGA controller detects that the hardware command queue is nearly full some of the commands will be swapped into the off-screen area. Then, when the controller finishes with existing commands these off-screen commands are read back first as the next command in the queue. In SiS 530's integrated 3D VGA controller both the 2D and 3D engines use the same hardware queue and off-screen command queue but since only one is active at any given time correct execution of commands is guaranteed.
The Setup Engine is one of the most important components of any of the new wave of 3D graphics chips. Taking over the CPU's duties by computing the thousands of calculations for preparing primitive drawing it has greatly diminished the bottleneck created by earlier graphics engines. The 32-bit floating point Setup Engine of SiS 530's integrated 3D VGA controller can finish all of the computations for triangle setup in 60 memory clocks - roughly ten times faster than a Pentium 200 CPU. Moreover it can compute line and point calculations in a lot fewer memory clocks than those required for triangle setup and was designed to fit all data formats within MS Direct3D API.
Once the Setup Engine if finished doing these calculations it forwards them directly to the Rendering Engine within 1 memory clock. While the Rendering Engine is drawing the triangle the Setup Engine gets busy calculating the parameters for the next one.
The integrated VGA controller's Rendering Engine is a pipeline structured drawing device comprising the Shading, Texture and Post Engines. The shading engine outputs pixel color representing the shade of a primitive while the texture engine is responsible for attaching texture color to the pixels. The post engine performs operations such as fogging, alpha blending and dithering.
In order to support high quality texture mapping the controller supports point-sampled, linear, bilinear, and trilinear texture filtering. With it's large 16kbit texture cache the integrated VGA controller can maintain the same fill rate no matter which filtering method is used, (trilinear filtering - best for video, maintains a 1/2 ratio fill rate). Many 3D controller chips do not have integrated texture caches and need to constantly fetch textures from framebuffer memory. When textures are constantly reused it slows down the processing to be constantly fetching textures so caching of textures can provide a significant performance increase.
- SiS 530 Graphics Performance -
The following screenshots were derived from the 3DMark"! 99 image quality tests at a screen resolution of 640x480. Click on the pictures for a larger view, or if you'd prefer the images and their reference images you can download the quality.zip file here...
The quality is not the best. Although the images are vivd and colors are good there are some distinct problems with the way the textures are rendered and there is no evidence of anti-aliasing whatsoever as you can see a bit better in the cropped images below...
Image Generated by SiS 530
As I stated at the beginning of this series, drivers for the SiS 530 are still rather primitive and this should be taken into consideration when reviewing these performance marks. The first drivers I received from SiS performed well in 2D but were incapable of rendering any benchmark scores in 3D applications. Now after three BIOS updates and with the help of a newer, yet still primitive and unoptimized set of graphics drivers, the chips capabilities have begun to come to light. Please note that these are preliminary findings and that the scores reflected below were in part submitted to the SiS 530's Project Manager who deemed them low. I was also informed that new graphics drivers were to be released today that would significantly improve performance. The testbed for benchmarking remains the same as in Part Two of this review and I will be updating these performance marks as soon as I get the newest drivers...
It is a little easier to make a comparison of SiS 530's performance using FutureMark's 3Dmark"! 99 Pro 3D benchmarking application. Processors were used at their default clock speed and external CPU frequency and run at a color depth of 16bpp.
As you can see the SiS 530's integrated 3D VGA Controller even with the primitive drivers seems to out perform Rendition's Verite V2x00 graphics card at 800x600 and very near the Rage Pro from ATI. The full battery of tests run with AMD's K6-2 350MHz - with the exception of Image Quality tests (which could not be performed) - generated the scores in the following table:
Please remember that the scores listed above are very preliminary and should be greatly improved with the release of new optimized drivers. I will be posting updated scores by the end of next week which will include popular game frame rates and screenshots. For now, the integration of a 3D VGA controller within the core logic chipset could create a major shake-up in the sub $800.00 SOHO and workstation market and could be a great boon to the laptop market. While it isn't conceivable at this time to expect the performance of the latest nex-gen graphics chips, the idea that it's possible to even develop so many integrated components into such small packages only leads to a more exciting view of the future of the PC.© 1998/99 2000 MediaTek