Snapdragon 610 & 615: Qualcomm Continues Down its 64-bit Warpath with 4/8-core Cortex A53 Designs

The unexpected arrival of Apple's first 64-bit ARMv8 core (codename: Cyclone) at the end of last year forced a transition to 64-bit sooner than expected. Silicon vendors keep telling me that both quad-core and 64-bit support are now borderline requirements for customers in China. I'm still skeptical that the Chinese market wouldn't respond just as well to a really well designed, high performance dual-core 32-bit SoC, but since there isn't one on the market we'll never really find out.

In order to quickly respond to market demand for 64-bit and tons of cores, Qualcomm is bringing ARM's own IP higher up the product stack into the new Snapdragon 610 and 615. Both SoCs are being announced at MWC, with shipments to customers in Q3 and the first devices hitting the market sometime in Q4 of this year.

The Snapdragon 610 and 615 are four and eight core implementations of ARM's Cortex A53, combined with Qualcomm's Adreno 405 GPU and the company's own 9x25 derived Category 4 LTE modem. The SoCs are built on a 28nm LP process, like the Snapdragon 410. The two new SoCs are also pin compatible with the Snapdragon 410, offering phone vendors an easy way of designing a higher performance version of a 410 platform.

That's the high level take, now let's dig a bit deeper.

New to the Roadmap: 64-bit and Octa-core

Like the Snapdragon 410, both the 610 and 615 use ARM's 64-bit Cortex A53 CPU IP. The main difference between the two SoCs is the number of cores. The 610 features four Cortex A53s, while the Snapdragon 615 features eight. Qualcomm readily admits that the Snapdragon 615 exists almost entirely because of the China market. I really do wonder if both the 610 and 615 have eight CPU cores with four fused off to make a 610, as creating two separate masks/die at this price point may not make a ton of sense.

I briefly went over the architecture of ARM's Cortex A53 in my post on the Snapdragon 410. In short, it's a 64-bit ARMv8 Cortex A7 on steroids. ARM views the Cortex A53 as the absolute furthest you can push a dual-issue, in-order microprocessor. It's going to make for an excellent performer in the mainstream.

Both SoCs are built on a 28nm LP process. The 8-core Snapdragon 615 is made up of two quad-core clusters, each optimized for a different operating point. One cluster is optimized for low power operation while the other cluster is optimized for high performance. This will likely manifest in four cores being able to run at a higher frequency than the other four, although Qualcomm tells me that all eight cores can be operational at the same time should a workload demand it. More likely than not we'll see situations where you have either the low power or high performance cluster operational, and not both. There simply aren't many (any?) normal use cases where you need 8 active cores. 

This dual-cluster approach should sound a lot like NVIDIA's 4+1 architecture. While the Snapdragon 615 meets the core count requirements for success in China, it also offers a bit more dynamic range for regular users as well.

I do have to point out that the Snapdragon 615 violates Anand Chandrasekher's Things that are Dumb list, but again it seems like Qualcomm is simply doing what the Chinese OEMs want. I could have a longer discussion about whether or not it's smart to listen to your customers if they are leading you astray, but let's see how this one pans out once Qualcomm shifts back over to its own CPU core IP next year. 

The big upgrade over the Snapdragon 410 actually comes on the GPU side as both the 610/615 integrate Qualcomm's Adreno 405 GPU. It's unclear how Adreno 405 compares, performance-wise, to Adreno 420 in the Snapdragon 805 but we do see a substantial feature set increase with the move to a 4xx GPU. Qualcomm's Adreno 400 GPU family is designed in house and brings a D3D11-class feature set to Qualcomm's mobile SoCs. There's support for hardware tessellation, DirectX 11.2, OpenGL ES 3.0 and full profile OpenCL 1.2.

I don't have many details about the ISP, but Qualcomm tells me to think of the 610/615 as bringing features down from the Snapdragon 800 family rather than bringing features up from the 410. The 610/615 also add hardware HEVC/H.265 decode acceleration.

The Snapdragon 410, 610 and 615 all have the same pinout, which implies that they all have the same 64-bit LPDDR2/LPDDR3 memory interface.

Connectivity and Conclusion

On the modem front all three 64-bit SoCs integrate Qualcomm's 3rd generation LTE, basically a derivative of the 9x25 core that we've seen used for a while now. There's support for Category 4 LTE and optional Carrier Aggregation. The new 610/615 are compatible with Qualcomm's RF360 front end, which we expect to see fully deployed and available in a device by the end of the year. Continuing with Qualcomm's tradition, the new SoCs also integrate its 802.11ac WiFi.

Given Qualcomm's very public statement against 8-core mobile CPUs back in August of 2013, I can only assume that the 8-core Snapdragon 615 is a very new addition to the roadmap. I do wonder what might've filled this space had Apple not released the A7 when it did. I also wonder what the 64-bit successor to the Snapdragon 805 will be. It's too early for Cortex A57 but I wouldn't rule that out for a future 800 series Snapdragon SoC.

The Snapdragon 610 and 615 appear to fulfill Qualcomm's desires for bringing 64-bit designs to market as quickly as possible, as well as the need to compete in the core count race in China. I don't agree with either philosophy, but I'm also not tasked with selling SoCs on a global scale - perhaps this is the only way. It also highlights a serious weakness in ARM's roadmap: anyone looking to build a 64-bit performance mainstream SoC is forced into tons of low power cores rather than fewer, higher IPC cores. We need a 64-bit version of the Cortex A17.

I do wonder how the Cortex A53 will measure up to Krait 300. The latter isn't incredibly out-of-order, but it can run at relatively high frequencies. Since we're talking about 28nm LP designs, I'm not expecting super high frequencies out of Cortex A53. This may be one of the few times in recent history where we get to pit ARM's own design against a similar, competing solution from Qualcomm.

Moving the needle on graphics is important and it's good to see quick progress on that front. I suspect both of these SoCs will make for good midrange devices.