In our article looking at
XBOX 360’s graphics processor, the ATI Xenos, we saw the first implementation of a unified shader core, whereby both Pixel Shader programs and Vertex Shader programs are executed over the same hardware block, as opposed to having separate vertex and pixel shader engines – its expected that ATI’s PC graphics accelerator for DirectX 10 (
see previous report) will also feature a unified shader architecture and NVIDIA are now talking about such a platform (having initially said that they believe separate discrete units would be more optimal in terms of processing performance). With a traditional architecture, utilising separate vertex shader and pixel shader engines, if the workload is unbalanced in relation to the quantity of processing units available at each end then one part of the pipeline may frequently stall waiting for the other, in which case some of the chips processing capacity is wasted; the advantage of a unified architecture there is jut one pool of units for both pixel shading and vertex shading and the workloads can easily be balanced such that no shader processing units are wasted whether the workload is primarily vertex or pixel shader bound.
Because of the balanced nature of a unified shader architecture we hypothesized that an ideal target market for such a platform may be mobile devices where size and costs of a chip are highly important. Highlighting that notion, today
PowerVR have announced their PowerVR SGX Wireless Graphics Accelerator Core, featuring a unified shader platform.
As with PowerVR’s MBX core, SGX (formerly Eurasia) is aimed for future mobile graphics processors, and will be available in three variants - SGX510, SGX520 andSGX530 – which we assume all are differentiated by the number of processing ALU’s . All of the cores are fully programmable and are said to have shader functionality greater than the level of DirectX’s Shader Model 3.0 or OpenGL2.0 and also follows PowerVR's rendering approach, being a Tile Based Deferred Renderer.
PowerVR’s business model relies solely on IP sales and as PowerVR appear to just be announcing the availability of the SGX, if the development of MBX is anything to go by, it may still be some time before SGX is implemented within silicon.
