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AMD's Kabini: Jaguar And GCN Come Together In A 15 W APU

The First APUs With AMD's GCN Architecture, Plus Power Management

In addition to a redesigned x86 core architecture, Temash and Kabini are also AMD's first APUs sporting the Graphics Core Next architecture.

Insofar as it applies to API support, the GCN-based logic built in to Kabini and Temash is identical to AMD's discrete parts. DirectX 11.1, OpenGL 4.3, and OpenCL 1.2 are all supported. The fixed-function Video Codec Engine is present, accelerating video decode and H.264-based encoding. Of course, this feature requires third-party developer support, and adoption has been slow thus far.

A new component of the VCE is called scalable video encoding, or SVC. This is able to encode multiple streams in one output pass, creating content that can be pushed to backwards-compatible devices. In other words, you're able to scale temporally and spatially, enabling playback at less demanding bitrates on lower-end hardware.

Like the Zacate-based APUs with the Cedar graphics core, this APU's graphics engine is identical across the line-up, differentiated only by clock rate. Every Kabini and Temash processor comes equipped with two compute units, each with four texture and four vector units. As you can see in the visualization above, a vector unit contains 16 ALUs and a register file. All told, one APU plays host to 128 ALUs and eight texture units. A single render back-end facilitates four full-color raster operation pipelines. Put more simply, think of this as one-fourth of a Radeon HD 7750, with lower clock rates and less memory bandwidth.

There are some notable differences between these APUs and AMD's discrete GPUs, though. For example, the GCN-based GPUs we've reviewed thus far all employed two asynchronous compute engines, which dispatch work to the compute units. In Tahiti, two ACEs served 32 CUs. Here four ACEs serve two CUs. Also new is a set of flat instruction accesses that allow an address to be issued in a load/store operation. This purportedly makes function calls simpler.

AMD says the new APUs support Ultra HD (2160p) output over HDMI and DisplayPort, Wi-Fi-certified Miracast, DisplayPort panel self-refresh to cut power consumption on compatible displays, dynamic refresh rates to save power when screen updates aren't necessary, and dual-display Eyefinity.

Power Management

Temash and Kabini use logic in each x86 core to calculate instantaneous power based on weight events and leakage. That result is fed into a power control unit called the Turbo Core Manager, along with GPU power and the on-die Fusion Controller Hub's consumption. A fourth input from the display interface yields a pretty complete picture of what each APU subsystem needs from the total available TDP. Using a credits-based system, Turbo Core can then change the chip's P-states, optimizing performance within a thermal ceiling.

AMD adds even more practicality to its power monitoring capabilities with the Turbo Dock concept. This hybrid form factor leverages active cooling inside a detachable keyboard to increase cooling performance and potentially double the platform's thermal ceiling.

As a result, you can use an APU-powered tablet on its own and still get a reasonably-fast experience, or dock with the keyboard to improve performance substantially.