GRAPHICS PROCESSOR

 
 

The graphics chip to be used in the Dreamcast is NEC's and VideoLogic's PVRSG. This chip was designed by Videologic PLC, and NEC will be the manufacturer of the chip. It has been rumored that NEC paid SEGA $150 million if SEGA uses the PVRSG in the Dreamcast. Lets see at $30 each for the Highlander, that must mean, that the first 5 million chips are free. This amount is so large that it is highly unlikely that NEC had made such a offer, since they are in the business to make a profit. VideoLogic engineers have been working on the design of the PVRSG for at least 2 years. NEC has indicated that the PVRSG is as powerful at the 3Dfx's Voodoo 2 while including 2D hardware, which the Voodoo 2 does not contain.  
  
Since some of PVRSG details are not available yet, we will list here the specifications for Videologic's latest PowerVR graphics processor the PCX2. There was a PCX1 chip which had the same specs as listed below for the PCX2 except for one difference, the PCX1 was unable to do bilinear filtering of textures.  

 
PCX2 Specifications:  

  • 66 MHz processor incorporating ISP (Image Synthesis Processor) and TSP (Texture & Shading Processor) function
  • 32 processing elements in ISP module
  • On-chip 12K ISP and 4K TSP parameter caches
  • Single SDRAM external interface for texture and parameter caching
  • PCI 2.1 interface
  • True shadow generation and per pixel fogging
  • Bilinear and adaptive-bilinear interpolation
  • Perspective-correct texturing and anti-aliased textures
  • 32 x 32 to 256 x 256 texture bitmap sizes
  • 1 to 4 MB texture memory
  • Texture formats:
    8-bit (2,3,2) RGB
    16-bit (5,5,5) RGB
    16-bit (4,4,4,4) RGBT
  • 32-bit Bus at 66 MHz, 264 MB/sec peak texture memory bandwidth
  • Smooth shading
  • Flat shading with offset highlights
  • 24-bit mixing of texture, lighting, and shading
  • Exponential fogging - with programmable fog color
  • Accumulation buffer - to allow multiple layers of translucency
  • Translucent textures - 16 levels per pixel
  • Global translucency allows objects to fade - 16 levels
  • 24/16 bit RGB and 16 bit dithered RGB modes
  • Manufactured in NEC's leading 0.35-micron process
  • Packaged in a 208-pin PQFP
  • Can use either SGRAM or SDRAM
  • Operating voltage of 3.3V
  • Bus interface - PCI bus 2.1 standard

Performance

9 Billion operations per second (max.)
1.2 Million polygons per second (max.)
66 Million pixels per second fill rate (max.)

Additional Details

Real shadows can be cast from any object over any surface, and updated every frame. 
PowerVR s equivalent 32-bit Z buffer makes solid outdoor objects a reality. 
Pixel perfect hidden surface removal. 
Anti-aliased textures using PowerVR's mip mapping stops shimmering. 
Perspective-correct textures do not bend because PowerVR performs a division per pixel. 
Smooth shading does not change when rotated. 

  • Translucency can be applied to whole objects, polygons, or individual pixels for effects like dirty glass, fire, water, and even simulated lens flare and radiosity. 
  • True logarithmic fog calculated per pixel. 
  • Real color, real time, real resolution (24-bit RGB, 30 to 60Hz, 640 x 480) with mip mapping, fogging and shadows over the whole scene.
  • Bilinear and adaptive bilinear filtering eliminates blocky pixels, leading to smoother, more realistic images. Curves look round and complex explosions look stunning.
  • Dithering from 24-bit, or "true color," to 16-bit color provides the true color look on standard 16-bit PC graphics systems, giving a more photorealistic image on mainstream PCs.
  • Compositing 2D and 3D on the PX2 accelerator significantly reduces system overhead, giving more cycles for 3D polygon processing. 

PowerVR Series2 Features and Specifications 


  • under $100 US for the initial PVRSG PC graphics card
  • 2D/3D solution on 1 chip
  • deferred rendering of 200 Mpixels per second 
  • 1.2 million front facing, fully textured, lit and shadowed polygons per second with a peak rate of three million to four million polygons per second 
  • geometry can be triangles, quads, and polygon strips 
  • full CPU load balancing 
  • tile accelerator
  • full floating-point geometry and texture setup engine
  • performance that scales up with faster CPUs
  • 32-bit accurate floating point z-buffering with no RAM accesses 
  • unified frame buffer and texture memory 
  • VQ (vector quantization) texture compression with 10:1 compression ratios 
  • 2X AGP with sidebands and PCI (33MHz/66MHz) 
  • full alpha blending modes supported 
  • image super-sampling for full scene anti-aliasing 
  • perspective correct bilinear, trilinear, and anisotropic texture filtering 
  • perspective correct ARGB gouraud shading 
  • specular highlighting with offset colours 
  • environment mapping
  • hardware translucency sorter
  • volumetric effects (shadows, lens flare, etc) 
  • multiple fog modes 
  • bump mapping 
  • full DirectX and OpenGL blending modes (back-end multi-pass rendering with micro-tile accumulation buffers) 
  • 3D in a Window 
  • max resolution of 1600 by 1200 in 24 bit color 
  • 100MHz clock rate 
  • RAMDAC (230Mhz) 
  • manufactured in NEC's leading 0.25-micron process 
  • 2 to 32MB of 100 MHz SDRAM
  • MPEG 2 decode 
  • DVD-assist 
  • video IN and OUT 
  • full support for DirectX 6, which is due this July 
  • available late April 1998 for evaluation 
  • available in the marketplace: most likely June/July 1998

PowerVR Architecture Eliminates Z-buffer  

  • Tile based rendering
  • 32-bit virtual depth buffer has no bandwidth requirements or memory space requirements. This setup provides more space for the frame buffer and for texture data. 32-bits of accuracy for Z coordinates allows objects in a large game world to occupy more then 4 billion different positions, which would provide more accurate placement of objects in a game world.
  • Compared with Nintendo 64 9-bit Z-buffer which has bandwidth requirements and this bandwidth has to be shared with the rendering. This setup provides for less memory space for the frame buffer and for texture data. A 9-bit Z-buffer is quite limiting in a large game world since it only provides 512 different positions for the Z coordinates. 
  • Compared with 3Dfx Voodoo 16-bit Z-buffer which has bandwidth requirements and this bandwidth has to be shared with the graphics rendering. This setup also provides for less memory space for the frame buffer and for texture data.

Dreamcast Data Bus Advantage Over The PC  

  • PC CPU to PCI Bus allows a transfer of data at 32 bits at 33 MHz resulting in a transfer rate of at most
    132 MBytes/second.
  • SH-4 to the PVRSG Bus will allow a transfer of data at 64 bits at 100 MHz resulting in a transfer rate of 800 MBytes/second, which would give it a distinctive advantage over the PC using the PCI bus. 

API's Available  

  • SEGA's own graphics API called Dragon
  • Videologic's PowerSGL Direct
  • Microsoft's Direct 3D
  • Silicon Graphics OpenGL

PC Ports Easy?  

  • D3D games and OpenGL games would port quite easy to the Katana due to these two API's being available for the PowerVR achitecture.
  • SGLdirect game ports would be easy and quick. Sega even recommends for software companies to start programming on PC's with a PowerVR graphics card now before Katana hardware development kits have been released. Katana hardware and software development kits will be delivered to developers in March of 98.

Additional Information Links  

 

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