Betting On Bay Trail: Intel's Atom Overhaul Tested

Design and Power Gating

Like Clover Trail, Bay Trail is a full system on a chip, or SoC. This time, however, Intel hasn't just integrated an advanced CPU core -- it's using its own GPU cores as well. Bay Trail includes four of the same Execution Units (EUs) that were used in Ivy Bridge. These chips can clock up to 667MHz. As far as we know, these are direct ports from Ivy Bridge, which means each EU can handle up to eight threads (total of 32) and has two texture samplers for a total of eight.

A great deal of work has gone into re-architecting the various components of the SoC, including a central storage block that ties the SDIO, SDcard, and eMMC storage controllers together, support for USB 3.0 baked into the chipset, added support for DisplayPort 1.2, and the ability to power gate the rest of the graphics chip while decoding video.

Four EUs isn't a great deal of graphics horsepower, compared to other current gen tablet SoCs, but it's a significant leap forward for Bay Trail. Previous iterations of Clover Trail used either a single SGX545 or a pair of SGX544 cores. The EUs inside  SoC support DX11, OpenGL ES 3.0, and, while Intel doesn't specifically call it out, should also support Shader Model 5.0 (based on Ivy Bridge's GPU). It's not clear if this iteration of the core includes a separate graphics-specific L3 cache or not. Ivy Bridge chips with HD4000 cores had a separate cache hooked directly to the GPU, but Intel couldn't tell us if Bay Trail retained this feature.

Bay Trail can output audio and video simultaneously over either HDMI 1.4 or DisplayPort 1.2. HDMI 1.4 output is limited to 1920x1080, but DisplayPort can output at up to 2560x1440. 1920x1080 should be more than sufficient for the vast majority of tablet owners, but it'll be up to OEMs which standard they integrate for video out.

Clock Gating

Like Clover Trail and Intel's high-end products, Bay Trail is also capable of monitoring multiple clock domains simultaneously and adjusting the SoC's clock speed to put MHz where they're needed most. That's fairly standard these days, but Intel's graphs suggest that they've further enhanced the flexibility of the underlying system for finer-grained control.

In this slide, the first CPU core is clocked three steps above standard while the other three CPU cores are quiescent. The GPU and Display power domains are both running faster than standard, while the camera is deactivated. This suggests that Bay Trail has added additional flexibility by allowing for variable clock speeds in areas beyond the CPU and GPU. How much of an impact this has on total power consumption remains to be seen -- while it's good to have the option, idle onboard cameras don't typically draw much power.

These changes, however, are part of a comprehensive Intel plan to introduce more efficient clocking and power management at every stage of the device. We've talked before about how the company is pushing plans for DevSleep on SSDs, SATA link power management, deeper CPU sleep states, and optimized PCI-Express power consumption alongside display panels with self-refresh. Many of the benefits introduced here, with Bay Trail, are further steps along the path towards power-optimized platforms at every level, rather than solutions that rely solely upon intelligent CPU/GPU power gating to hit targets.

That's the high level overview of Intel's Bay Trail architecture and its new capabilities. Let's look at performance.

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