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Power Management and Turbo Core

Lowering power consumption was one of the major goals during Llano development. As we remember, processors with K10 microarchitecture were not particularly modest when it came to power consumption. And now besides the x86 cores they also have a powerful graphics core to deal with. So, AMD had to find a way to improve power consumption rates, otherwise Llano wouldn’t be able to take a decent place in the contemporary processor market, and especially in the mobile segment, where APUs with powerful integrated graphics may be especially needed.

The problem of high power consumption was partially solved when they started using new manufacturing process. 32 nm technology helped lower Llano’s core voltage to about 1.2-1.25 V, i.e. to the level of energy-efficient Athlon II modifications.

However, the major innovation is the ability to disconnect idle APU parts from the power rail via Power Gating. Although there are only two independent power lines assigned to Llano processors in Lynx platform – one for processor cores and one for the graphics core and the North Bridge – the power management system can power off selected processor units in a very flexible manner. Namely, the individual x86 cores, the graphics core or the UVD unit built into it can all be powered off independently.

As a result, AMD managed to design desktop processors with 100 W and 65 W TDP, and mobile processors with 45 W and 35 W TDP. In other words, AMD has finally come up with processors, which heat dissipation is comparable with that of Intel Sandy Bridge CPUs.

However, the TDP limitations resulted in pretty low clock speeds for Llano processors. None of the currently available models reaches 3 GHz threshold. As for the mobile products, their clock frequency doesn’t go beyond 2.6 GHz.

In this case AMD decided to use all available means of boosting their processors performance, including Turbo Core dynamic overclocking technology, which increases the clock frequency if some of the computational cores are idle. They have already implemented this technology in Phenom II X6 processors, but they did modify it a little for Llano. In the APU they determine the possibility to increase the processor clock frequency judging by the core utilization levels rather than their temperature. Temperature is secondary in this case: if it exceeds certain limits it may simply cause the Turbo mode to shut down.

The benefit of the new Turbo Core implementation is that in general case it produces repeatable results and almost doesn’t depend on the cooling system efficiency or the ambient temperature.

Unfortunately, dynamic overclocking technology in Llano processors is only applied to computational cores. The graphics core can only lower its frequency in order to reduce the power consumption and cannot speed up automatically. However engineers took into account the fact that when the graphics core is in full-speed mode, its power consumption increases, so if the x86 cores switch to Turbo mode in this case, the overall power consumption may get out of hand. Therefore, in 3D or Fusion applications that actively use graphics core stream processors Turbo Core technology may not kick in even if only one processor x86-core of the four is active.

 
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