Medfield, Intel’s x86 Phone Chip

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While Intel has historically developed their chips internally and avoided third party IP, there are exceptions. When it comes to mobile graphics and video, Intel (along with Apple and most SoC vendors) has historically relied on licensing IP from Imagination Technologies. In fact, Intel owns a fairly large share of the company, slightly over 16%, demonstrating their significance as a partner. Apple similarly owns around 9.5% of the small British IP firm and uses PowerVR in the iPhone and iPad. Other notable licensees include Texas Instrument’s OMAP line, Samsung and Mediatek.

Imagination is the dominant mobile graphics IP provider because the PowerVR architecture is incredibly power and area efficient and has excellent support for modern APIs. PowerVR is a tile-based deferred rendering (TBDR) design that was briefly available for the desktop market in the form of the Kyro and Kyro II. The key advantage of TBDRs is that they are inherently cache-friendly. Storing all the relevant data for a tile in SRAM is quite feasible and dramatically reduces the bandwidth requirements and power consumption for rendering.

Moorestown has a 400MHz implementation of the PowerVR SGX535 on a 45nm LP process. This is twice the frequency of any other SGX535 design, and a testament to Intel’s process technology and design team. The theoretical single precision shader performance is 3.2GFLOP/s.

The Medfield graphics have been upgraded to take advantage of the 32nm node in a power efficient manner. Penwell integrates the newer SGX540, which has twice as many shader cores as the previous generation and maintains the same 400MHz frequency. This should not be surprising, as Intel’s key objective was to reduce power compared to the 45nm Moorestown. So the obvious approach to increase graphics performance is building a wider GPU, in this case the 4 shaders achieve 6.4GFLOP/s. Intel claims peak throughput of 40MTriangles/sec and 2GPixels/sec for the front-end and back-end of the 3D pipeline.

The one drawback of the newer SGX540 architecture is that it only handles the PVRTC and ETC1 texture formats; not DXTC, which is required for Windows and DirectX. Clovertrail, the tablet variant of Medfield will presumably use a newer DX-compatible GPU, perhaps the SGX544MP2.

Video Codecs and Display

Both the video encode and decode IP for the previous generation Moorestown were licensed from Imagination Technologies. While there are not any comprehensive benchmarks, Moorestown was designed for 1080p playback, using H.264 high-profile at 20mbps. However, this was a fairly taxing workload and would often impact the performance of any other concurrent tasks. Video encoding was available in 720p resolution at the H.264 base profile.

In tandem with the graphics, Intel has implemented new video codec blocks from Imagination for Medfield. The decoder is a bit more powerful and can handle 40mbps playback; while it is officially rated for 1080p30, Intel claims that it can often achieve 1080p60 smoothly (and without causing problems for other applications). That will be an interesting area for reviewers to investigate in the future, especially for different models that might be configured with less memory bandwidth or lower frequencies. The video encoder received much more attention and can handle H.264 1080p encoding, but only at base profile.

The display interfaces are also much more robust for Medfield. The display controller has three pipelines. There are two MIPI-DSI interfaces, with 4 lanes, for internal displays at up to 1366×768. External displays use an HDM1 1.3a port with support for 1080p30 and 1080i60 resolutions. In contrast, Moorestown was limited to a single internal display with either LVDS or a lower resolution 1024×600 MIPI, and the HDMI was actually in the external Langwell hub.


The other major block in smart phone SoCs is a DSP-like processor for imaging functions, such as stabilization, auto-focus, white balancing. In theory, this could be done on a programmable GPU; however OpenCL is still new for PC-class systems, let alone mobile phones. Moreover, the power efficiency of image signal processors (ISPs) is dramatically higher than GPUs, because they are tailored to the application and fundamental datatypes. Moorestown was limited to a single 5MP camera could also record at 720p video, which is not particularly impressive. The ISP was a basic fixed function design that was rated for 90Mpixel/sec.

Medfield was designed for two discrete camera sensors that can record video at 1080p. The primary sensor interface is for a high resolution 5-24MP sensor, while the secondary is for a modest 2MP sensor. The ISP is a brand new design licensed from Silicon Hive, which was a spin-out from Philips. Ironically, Intel actually bought the company in 2011 as part of series of acquisitions to strengthen the mobile product portfolio. The ISP is fully programmable, which is fairly unique within the industry. The programmability offers a number of advantages; vendors can differentiate their offerings by developing custom imaging libraries, and the camera can effectively be upgraded over time. The programmable ISP is rated at 240Mpixel/s, which is quite high performance and more than sufficient for 1080p recording. The full benefits of the programmable ISP will be more visible once vendors have started shipping products with customized imaging.

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