Embedded Computing Down To Two Major Camps

By Pallab Chatterjee
The 2011 CES show was highlighted by the large number of tablet computers and mobile devices that support Internet access. The form factor for these devices is based on use models, but the computing capabilities are based on the power and operational life between charges. The platforms are drawing diving lines between x86 cores vs ARM cores, and CPUs vs GPUs.

While on the high level the tradeoffs were on screen size, battery life, UI and apps available, the hardware battle for the BOM was with a much smaller set of players. These new tablets were derived from either smart phones or laptops. The ARM CPU selection is the dominant platform for the oversized smart-phone derived products. The x86 CPU selection is the dominant platform for the reduced function laptop computer products.

The ARM devices are available in multiple forms. These include straight single and multicore CPUs, embedded CPUs in graphics chips, and full mobile chipset with memory controllers and display control. These can be found in parts from Nvidia, the Tegra products, and parts from Marvell and Qualcomm such as the Snapdragon products. In a lot of the cases, these ARM cores are combined in systems with MIPS cores and graphics acceleration from Imagination Technologies.

The ARM platform is highly power optimized for battery operation and for the RF interface. The key driver for the platform in the tablet space is the development environment. The platform software, available from both ARM and third parties, covers bus architecture for multicore design, operating system functions and high-level applications. To complete the tablet design, there are many suppliers making compatible IP for USB, HDMI, microphones, headsets, eSATA, and other components that have firmware interoperability with ARM. The majority of the ARM-based designs shown used the Android operating system rather than cell phone OSes.

The x86 platforms are primarily coming from the business applications and higher data throughput side. The main chipset uses Intel Atom cores, and some of the “lighter” duty reduced function tablets featured VIA x86 cores. These platforms were running Windows derivatives and Linux. The highly promoted Moblin environment was not really present in the new product mix. These x86 products have separate CPUs and GPUs. They feature either Intel graphics or Nvidia graphics co-processors. These tablet chipsets are lower-power versions of the one in the netbook/ultra-light laptop market and several also included the Imagination Technology POWERVR graphics and shader engine.

As the tablet form factor does not allow for a fan and has thickness that is driven by the height of the peripherals connectors, balancing power for the applications is the major challenge. Some of the new tablets released played with the options of single core CPU, multicore CPU, single GPU, multi-GPU, and a hardware codec. As one of the high-power and high-use applications is for playback of video and displaying high-resolution graphics, efficient utilization of the H.264 codec is a key.

Based on the compression involved with the data and the length of the video streams being viewed, there are power tradeoffs doing the video decoding in a CPU or a GPU with software vs. a hardware codec. There are similar issues for the camera interface if it supports stills, video, and single/dual/triple (S3D on one side, single on other) data streams going to a single codec. The format for the tablets affects not only the configuration of the cores but also their duty cycle. If a single part gets an extended operation, this changes the thermal gradient on the die and the board—hence the software has to balance the activities to help balance the heat.