ARM updates mid-range offerings, intros Cortex-A17 CPU


— 12:01 AM on February 11, 2014

The world of ARM processors already has tremendous variety, and it's becoming a little bit more robust today with the announcement of the Cortex-A17 CPU core, along with a new video processor and display controller.

In order to understand where the Cortex-A17 fits into ARM's product stack, we should probably take a quick tour of what's there now. ARM essentially offers three different classes of CPU microarchitectures in the Cortex A-series, all of them intended for consumer devices.

The smallest of these is the Cortex-A7, a tiny core with very low power requirements. ARM has also released a new derviative of the A7, the Cortex-A53, that's compatible with the 64-bit ARMv8 instruction set architecture.

On the other end of the spectrum is the Cortex-A15, one of ARM's largest offerings, although it's still been shoehorned into a number of high-end smartphones. The 64-bit ARMv8 derivative of the A15 is the Cortex-A57.

In between the two is the mid-range Cortex-A12. This 32-bit core is the successor to the immensely popular Cortex-A9 that powered a number of seminal smartphone and tablet designs. The A12 was arguably a little late to market, and it doesn't yet have a 64-bit ARMv8-compatible equivalent in ARM's IP portfolio.

When we first heard that ARM was announcing a mid-range update in its CPU lineup, we thought perhaps the 64-bit successor to the Cortex-A12 was about to debut—presumably the Cortex-A55, if the naming convention works as expected. However, what we're getting instead is an update to the A12 known as the Cortex-A17.

The A17 is based on the same basic microarchitecture as the A12, but it has received an upgrade to its connectivity to the outside world by adopting the AMBA4 interconnect. This interconnect gives the A12 a faster path to the memory controller, which means higher performance and effectively better power efficiency. ARM claims the Cortex-A17 is 60% faster than the old Cortex-A9 (although such claims are always subject to qualification and possible shenanigans.) Thanks to the new bus interface, the A17 also supports full memory coherency for operation in multi-core SoCs, which means it's capable of participating in ARM's big.LITTLE power-saving scheme.

The idea behind big.LITTLE is that tasks should be shifted around to larger or smaller cores depending on their performance requirements. Matching the task to the right architecture can yield efficiency gains similar to those provided by dynamic voltage and frequency scaling (DVFS) schemes used in larger PC processors—or perhaps even better.

The first big.LITTLE implementations were symmetrical, pairing four small cores with four larger ones, but ARM's vision for this technology is ultimately asymmetrical. You can imagine a future SoC for phones that has two relatively fast Cortex-A17 processors paired with four low-power Cortex-A7s. Such a config could provide relatively high per-thread performance when needed to keep the user experience snappy, while scaling back to the low-power Cortex-A7s for the majority of the device's background and maintenance tasks.

The Cortex-A17 IP is slated to become available to ARM partners at the end of the current quarter, and ARM expects devices based on it to ship to consumers at some point in 2015.

One point of minor intrigue here is why the firm chose to call this product the A17 rather than just making it another revision of the A12. (The Cortex-A9 went through a number of revisions without changing names.) ARM expects the A17's performance to approach that of the Cortex-A15, only with superior power efficiency. Giving this core a larger "number" than the A15 is likely meant to help sell it to consumers as an upgrade.

That's marketing for you, but given everything, it's probably a sensible choice. In practical terms, the A17 is probably a more fitting core for smartphones than the A15.

Then again, Apple's iOS devices have already begun moving to 64-bit CPU cores, so the pairing of the A12 and A7 may be more common among low-end devices and SoCs by the time it hits the market. The press release for the A17 includes endorsements from parteners like MediaTek and Realtek. ARM expects the ARMv8-capable pairing of the Cortex-A57 and A53 to grab a portion of the market, as well.

ARM's physical IP division, Artisan, will provide pre-baked POP implementations of the Cortex-A17 for 28-nm processes at both TSMC and GlobalFoundries.

In addition to the A17, ARM has also announced a new video processor, the Mali-V500, and a display controller, the Mali-DP500. These IP blocks are meant to accompany the Mali-T720 GPU in mid-range SoCs. The display controller supports ARM's AFBC frame-buffer compression, for a little cross-IP integration synergy action.

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