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Spectre Graphics Core

Codenamed Spectre, the integrated graphics core of Kaveri APUs features an updated architecture. The Richland’s graphics was based on the VLIW4 architecture whereas the new integrated GPU sports the newest GCN 1.1 architecture and can match up-to-date graphics cards in functionality (it has the same architecture as AMD’s Volcanic Islands solutions). Of course, the Spectre has much fewer shader processors than flagship Hawaii-based cards, yet it is classified as Radeon R7 and supports all modern APIs including DirectX 11.2, OpenGL 4.3 and Mantle.

The GCN architecture hasn’t changed much on its way from discrete graphics cards to APUs, so we see several compute units, each with 64 shader processors (IEEE 2008 compatible), 4 vector units and 16 texture-mapping units. In its maximum configuration the Kaveri’s graphics core may contain up to eight compute units combined with a geometry coprocessor and up to eight raster operators capable of processing up to 8 pixels per clock cycle (or up to 32 pixels with no color).

So, the Kaveri may have a total of up to 512 shader processors, being in-between such midrange graphics cards as Radeon R7 250 and Radeon R7 250X. AMD estimates the Spectre’s theoretical performance at 737 gigaflops but we must be aware that the gaming speed of an integrated graphics core is largely limited by the memory bandwidth rather than by the core’s shader processors. That’s why the Spectre is actually slower than the $100 discrete cards.

Besides the memory interface, the Kaveri’s integrated GPU has no limitations in its architecture compared to its discrete cousins. The Spectre can process and rasterize up to one geometrical primitive per clock cycle, has a large cache for storing primitive data, and features improved geometry and hardware tessellation performance thanks to data buffering optimizations implemented in the GCN architecture.

The Kaveri’s key feature which is emphasized by AMD is that the graphics core resources can be utilized for heterogeneous computing sharing the same system memory with the x86 cores. For that purpose, the graphics core incorporates eight independent asynchronous compute engines, which can work in parallel with the graphics command processor and serve up to eight instruction queues each. Each engine can access the APU’s cache and memory controller, implementing HSA technologies.

The asynchronous compute engines can actually work independently, allowing AMD to promote the Spectre as an additional eight processing cores. In AMD’s terms, a processing core is a programmable hardware unit capable of running at least one process in virtual memory independently of other cores. We just must keep it in mind that the GPU cores require special program code and may only be utilized by special software.

Talking about the functionality of the Kaveri’s graphics core, we must mention its TrueAudio coprocessor for hardware-accelerated dynamic 3D audio effects. As earlier, the processor incorporates dedicated engines, VCE and UVD, for encoding and decoding HD video content. Their capabilities have been enhanced once again. The VCE engine version 2 features improved encoding quality by being able to introduce B-frames in the YUV420 color space and supporting the YUV444 color model. The UVD engine is version 4 now and features higher stability when handling errors in video streams.

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