How AMD's Fusion A8-3850 APU Changes Personal Computing

Test system

The APU

AMD supplied us with their top of the line A8-3850 APU, which comes with the CPU clocked at 2.9GHz and the GPU including all 400 shader cores clocked at 600MHz. Similar to previous AMD CPUs, the APU will also reduce it's operating frequency and voltage to save power, when it is not fully utilized. The following table lists all available P-States and the default voltages used for them.

As you can see, the default operating voltages are quite high, considering the chip is manufactured using the 32nm manufacturing process. As we have published earlier, the chip lends itself to heavy undervolting. We'd like to note, that several tools can't properly read the core temperatures of the chip. According to Tamas Miklos, programmer of AIDA64 at FinalWire, at this point there is nothing that can be done about it. He told us, that the readout basically works the same way as for previous CPUs from AMD, but in this case the values are not correct. He continued to point out, that this is not the first time something like that happens. AMDs Athlon 64 “Brisbane“ chip for example also reported wrong temperatures, which could be corrected by an offset.

Also, the readout of the properties and/or temperature of the GPU with GPU-Z was errornous as well at the time of the review. Since Llano was still very new, it could very well be that those issues will be corrected in future releases of this software.


The Mainboard

Part of our Llano testkit was a Gigabyte A75M-UD2H micro-ATX mainboard. It is one of the more expensive Llano mainboards, which is due to it's very comprehensive feature set. With regards to display connectivity, there are all options available: D-Sub, DVI, HDMI and DisplayPort. When connecting multiple displays, please note that not every combination is possible. D-Sub and HDMI as well as DVI and DP are mutually exclusive. If you enable Dual Link DVI, all other ports are disabled. Also it is not possible to hotplug another display when the computer is running. Changing the display connection requires a reboot.

The mainboard supports controlling the fan speeds if the respective setting is enabled in BIOS. Whether you use 3-pin or 4-pin fans doesn't matter, they will be automatically detected.

Updating the BIOS was quite easily done using the Q-Flash utility, which can be invoked via F11 at bootup. The BIOS file simply needs to be put on a USB pen drive and can be selected from within Q-flash. The BIOS contained a plethora of settings which allow to tune almost every aspect of the platform. There are a few options that don't work properly though. There are settings to increase the multiplier of the CPU and the GPU clock beyond the default specifications. This only amounts to higher frequencies being reported by tools like CPU-Z, but the chip will not perform any faster. However, we'd like to note that AMD readies a unlocked Black Edition A-series APU, where these options might come in handy.

With the F3 BIOS update, a new option to enable “C6 mode“ was added to the BIOS setup. Apparently this option enables the use of the C6 sleep state, as idle power consumption dropped by almost 4W after the BIOS update.


The Memory

Kingston supplied us with a KHX2000C9AD3T1K2/4GX kit, a pair of 2GB modules specified to work up to DDR3-2000. This would be more than ample to supply the APU with the necessary bandwidth. However, with both the shipping BIOS (F2) and a beta BIOS (F3b), we weren't able to operate this memory at the DDR3-1866 setting. The slower DDR3-1333 and DDR3-1600 modes worked fine. After Gigabyte released the F3 BIOS update, also the faster DDR3-1866 mode worked without a hitch.

The memory SPD is programmed with conservative timings of 9-9-9-24 (CL-RCD-RP-RAS) at DDR3-1333 and 8-8-8-22 for DDR3-1066 for the default operating voltage of 1.5V. The SPD also contains Intel Exteme Memory profiles (XMP) for the high performance settings, which require a memory voltage of 1.65V but are unusable on an AMD based Motherboard/CPU. They contain programmings with CL9 up to DDR3-2000, CL8 up to DDR3-1776 and CL7 up to DDR3-1554. For DDR3-1333 there is even a CL6 setting available.

On Llano the XMP profiles are not supported by the BIOS, so we had to manually configure the timings to ensure best performance settings. This can be considered a minor hassle, but once you come up with a good working configuration you won't change the timings every now and then.