Just like desktop PCs before them, mobile devices will leap to multicore processors. The first dual-core smart phone, the LG Optimus, is now shipping with an Nvidia Tegra 2 processor. But this year, many other chip vendors will roll out multicore processors, giving designers of tablets and high-end smart phones many options to choose from. Sorting through these options can be a challenge.
Most of these processors use ARM’s Cortex-A9 CPU, available from ARM in a dual-core reference design. TI recently announced OMAP5, the first processor based on ARM’s next-generation Cortex-A15 CPU. The A15 will deliver up to 50% more performance per CPU than the A9, but OMAP5 won’t appear in phones and tablets until late 2012. Samsung and others are also working on Cortex-A15 processors, but they’re likely to reach the market no sooner than OMAP5.
Because it develops its own ARM-compatible CPUs, Qualcomm is on a different roadmap. The company is nearing production on its MSM8260, based on its first-generation Scorpion CPU. The Scorpion is similar in performance to the Cortex-A9, but at the recent Mobile World Congress (MWC), the company announced that products using its second-generation CPU, known as Krait, will sample later this year. Qualcomm expects Krait to deliver performance similar to that of the Cortex-A15. Marvell also develops its own CPUs, and its current Sheeva CPU matches up well with the Cortex-A9.
These processors are also distinguished by the number of CPUs. Most offer two, but Marvell’s Armada 628 includes a third core. This CPU, however, is only used for low-power operation, so the peak performance of the 628 is the same as a dual-core design. Freescale’s i.MX6 comes in a quad-core model, giving it a potential performance advantage. Like OMAP5, though, the i.MX6 is not yet sampling. Also, software must be rewritten to take advantage of its four cores.
Processors Deliver 3D Video
CPU performance is the most obvious differentiator, but multimedia is increasing in importance. Full HD (1080p) video decoding at 30 frames per second (fps) is a given in these high-end chips, but not all can handle the MPEG4 High Profile format used for Blu-ray and other high-quality video. The Tegra 2 falls short on this task.
Newer chips are promoting their 3D video capabilities. These chips can decode two 1080p 30-fps streams simultaneously, one for each eye. This capability is sometimes stated as 1080p 60fps. Some chips can even encode 3D video at 1080p resolution, allowing users to record their own 3D movies.
High-end processors are also pushing the limits of graphics capability. The top smart phones today operate their 3D engines at about 40 million triangles per second, enough to display complex and realistic images on a typical smart-phone display. Next-generation processors, such as the Armada 628, are instead targeting 200 million triangles per second.
This performance enables realistic images on larger tablet screens and on HDTVs, which can be driven through an HDMI connection. Also, this raw performance compares well to that of current video consoles such as the Xbox 360 or PlayStation 3, but it remains to be seen whether these superchips can actually deliver the same image quality on HD screens.
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Cellular Integration Reduces Cost
Another important design choice is whether to integrate the cellular baseband into the application processor, which can reduce the size, cost, and power of a smart phone. A cellular baseband takes time to achieve regulatory certification, so some designers keep it separate. Also, an external cellular chip provides more flexibility to select, for example, a WiMAX or Long-Term Evolution (LTE) baseband.
A standalone processor makes sense in tablets if the vendor intends to offer a Wi-Fi-only version, which doesn’t need the cellular function. Tablets sold though cellular carriers, such as the Motorola Xoom, don’t have this constraint. Even for Apple’s iPad, the cellular version is outselling the less expensive Wi-Fi-only model by a 2:1 margin, so tablet makers may choose to focus on cellular products.
If the designer prefers an integrated processor, the options are more limited. Qualcomm integrates cellular capability in all of its processors, including the MSM8260. At MWC, Broadcom announced the BCM28250, which also combines a dual-core processor with a cellular baseband. ST-Ericsson has been sampling the similar U8500 for quite some time but has struggled to bring the chip to production. These three processors support the latest HSPA+ 3G protocols but not LTE.
With two or more CPUs, 3D video, and powerful graphics capabilities, these superchips support tablets that challenge low-cost PCs and smart phones. They not only will provide speedy Web browsing and slick games, they also will connect to larger external displays to deliver sharable entertainment, serving as a movie player, media center, or even a game console and controller all in one. The chip makers are ready to deliver. Now, system designers must realize these visions.