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ARM Cortex-A73 core and Mali-G71 GPU target mobile VR

May 31, 2016 — by Eric Brown 2,414 views

ARM announced a 10nm Cortex-A73 architecture with 30 percent better sustained performance and efficiency than the Cortex-A72, plus a 32-shader Mali-G71 GPU.

ARM unveiled a follow-on to the high-end Cortex-A72 mobile architecture, which was announced in Feb. 2015, and also unveiled a high-end Mali-G71 GPU to work with it (see farther below). The Cortex-A73 supports a 10nm FinFET process, compared to 16nm FinFET+ for the Cortex-A72. Using this process, Cortex-A73 cores would measure 0.65 x 0.65mm, making it the “smallest and most efficient ‘big’ ARMv8-A core” to date, according to ARM.

Comparison of Cortex-A57, -A72, and -A73 performance (left) and core area
(click images to enlarge)

Like the 32-bit Cortex-A15 and 64-bit Cortex-A72, the 64-bit Cortex-A73 is intended for use as the more powerful “big” cores in hybrid Big.Little SoCs. ARM recommends Big.Little pairings with the Cortex-A53 or new, and similarly ARMv8, Cortex-A35. The processor supports up to quad-core SoC configurations with 64KB I-Cache, 32KB-64KB D-Cache, and up to 8MB L2 Cache.

Cortex-A73 based Big.Little pairing benefits
(click image to enlarge)

The Cortex-A73 enables clock rates of up to 2.8GHz, and offers 30 percent better “sustained” performance and power efficiency than the -A72, claims ARM. The Cortex-A73’s focus on better sustained performance should enable mobile devices to maintain peak performance for longer periods before being forced to throttle down due to heat buildup. The “cache coherent” design is especially useful for intensive processing applications such as mobile virtual reality and 4K TV.

Ten chip manufacturers are said to have licensed the Cortex-A73, including HiSilicon, Marvell, and MediaTek. Although primarily aimed at mobile devices, with the first phone and tablets appearing in 2017, the Cortex-A73 also supports applications such as “large-screen compute devices, industrial gateways, in vehicle infotainment, and smart TVs,” says ARM.

Cortex-A73 vs. -A72 performance (left) and power consumption
(click images to enlarge)

There were few additional technical details, but AnandTech took a deeper dive at ARM’s new Austin, Texas facility. The story refers to the Cortex-A73’s new “Artemis” microarchitecture as playing a key role in the new focus on sustained performance. According to AnandTech, the design is based as much on the 32-bit Cortex-A17 architecture as it has on the 64-bit Cortex-A72. The Cortex-A17 has seen fairly limited use in phones, with notable adoption by the MediaTek MT6595 and Rockchip RK3288 SoCs.

ARM Cortex-A73 core block diagram
(click image to enlarge)

Like the Cortex-A17, the -A72, implements shorter pipeline stages, with a 4-stage fetch stage instead of five on the -A72, and the ability to decode most instructions in a single cycle, compared to three on the -A72. The shorter stages help feed the overall design goal of offering the “best possible performance at the least possible power consumption,” says AnandTech. The publication notes that this is clearly a mobile-class, not a server-class design. For example, it uses a standard AMBA 4 ACE interconnect standard instead of AMBA 5.



ARM also announced a companion Mali-G71 graphics processing unit that has an even greater focus on mobile VR and AR (augmented reality) than the Cortex-A73. The GPU offers a 50 percent increase in graphics performance, a 20 percent increase in power efficiency and 40 percent more performance per square millimeter, claims ARM.

ARM Mali-G71 GPU block diagram
(click image to enlarge)

The Mali-G71’s support for up to 32 shader cores is twice the limit of the previous Mali-T880. The GPU uses a third-generation “Bifrost” architecture, which is “optimized for Vulkan and other industry-standard APIs, building on innovations from the previous Utgard and Midgard architectures,” says ARM.

HiSilicon, MediaTek, and Samsung Electronics have already licensed the Mali-G71 technology. The Mali-G71 is optimized for use with the Cortex-A73, but is not required. For its Cortex-A72-based MediaTek MT8173 SoC, for example, MediaTek ignored ARM’s suggested use of a Mali-T880, and instead went with a PowerVR GPU. This time, however, it’s sticking with the recommended pairing. ARM also recommends using the GPU with its Mali-DP650 (display) and Mali-V550 (video) coprocessors, respectively.

Further information

The Cortex-A73 and Mali-G71 should appear in mobile products in 2017, says ARM. More information may be found at ARM’s Cortex-A73 and Mali-G71 announcement and Cortex-A73 and Mali-G71 product pages.

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