Exclusive: Here are the likely specs of the Google Tensor chip in the Pixel 6

Ever since rumors arose that Google was developing its own chip for Pixel phones, one of the burning questions that we’ve been asked over and over again is: What are its specifications? Leak after leak have confirmed various tidbits about the Google Tensor chip, but none have confirmed details on the most important part: the CPU. A recent Geekbench listing purportedly from the Google Pixel 6 Pro sparked wild speculation online about the Tensor’s CPU, and we can finally address some of those theories thanks to our source.

All the Google Tensor rumors to date

First of all, a bit of context. In early 2020, various Korean sources and American news website Axios reported that Google’s “whitechapel” chip will be designed in cooperation with Samsung and fabricated on SLSI’s 5nm process. Rumors at the time claimed that Google’s chip will feature an octa-core ARM processor comprised of two Cortex-A78 + two Cortex-A76 + four cortex-A55 cores, an off-the-shelf Mali GPU from ARM, hardware optimized for machine learning, and optimizations for the company’s Google Assistant service. Given the challenges in developing a custom SoC, it made sense for Google to use existing CPU cores for its first mobile chipset, so these rumored specs seemed plausible to many.

Many months passed without any news on Google’s custom silicon until 9to5Google reported in April that the chip will debut on the Pixel 6 series. Finally, Google last month confirmed its plans to ship the Pixel 6 series with its in-house chip, called the Google Tensor. They also confirmed a few high-level details about the chipset, such as how its TPU is used to run HDRNet on every frame in a video, how the chip powers new on-device AI features, and how the chip protects user data with its second-gen Titan M2 module.

Google’s surprise announcement in early August confirmed most of the leaked information from last year, while confirmation for some of the remaining rumors came from other leaks. A comment left by a Googler on the Google Issue Tracker corroborated the tidbit about the off-the-shelf Mali GPU, which we now know is the Mali-G78. A teardown of an Android 12 beta release revealed the Pixel 6 will have a Samsung Exynos modem, which was later corroborated by Reuters. The last remaining spec that had yet to be confirmed was the CPU, which is why so much attention was put on this one Geekbench listing.

The Geekbench result that many assumed was from the Pixel 6 Pro. While we can never be 100% certain, we are strongly leaning towards this benchmark being legitimate. The build fingerprint, kernel version string, CPU frequencies, CPU clusters, GPU info, and more match the values from our source’s Pixel 6 Pro. It would be very unlikely for someone to have faked this listing, which would be possible but requires the person to know the exact values to fool our source who has real hardware.

Based on the incomplete CPU information in this listing, leakers such as Digital Chat Station extrapolated the CPU configuration of the Google Tensor chip. The most shocking part of this speculation for many was the suggestion that the Google Tensor CPU will have two Cortex-X1 cores, Arm’s most powerful Cortex CPU to date. In contrast, neither the Qualcomm Snapdragon 888 nor the Samsung Exynos 2100 have more than one Cortex-X1 core. If this chip also has two Cortex-A78 cores in addition to the dual Cortex-X1 cores, then the Google Tensor may be the fastest chipset on an Android device to date.

As many have noted, the Geekbench score falls well below the average Exynos 2100 Galaxy S21 and Qualcomm Snapdragon 888 device, which is strange considering the hardware in question. After speaking with Andrei Frumusanu, Senior Mobile Editor at AnandTech, we came to the conclusion that you can’t reach a conclusion about the true performance of the Pixel 6 Pro just from this one benchmark result. As he noted in our discussion, it’s hard to tell which core was stressed for the single-core part of the benchmark, and the core was seemingly locked to 2.15GHz anyway, which is well below the maximum frequency of the X1 cores. There are several factors that could have contributed to this underwhelming benchmark result, such as unoptimized DVFS or scheduler parameters, all of which could have prevented Geekbench from running the cores at their peak frequencies. If we want to find out how fast the Pixel 6 Pro is, we’ll have to wait for more people with the phone to run the benchmark.

Google Tensor specs from a real Pixel 6 Pro

While the benchmark doesn’t confirm the microarchitectures of the Google Tensor’s CPU cores, we were finally able to determine what are likely the designs for each CPU core thanks to our source. Yesterday, a source who has a real Pixel 6 Pro reached out to us, and we learned from his device that the tri-cluster core design and CPU frequencies revealed by that Geekbench listing are accurate. Following our report yesterday, we found the exact CPU parts in the Google Tensor chip, which are exposed to the system through /proc/cpuinfo, a file that is populated by the CPU itself and read by the kernel. Thus, the chances that it’s been spoofed are very low, though there’s a low possibility that Google themselves masked the CPU IDs in the output. We say it’s a low possibility because Google did not bother spoofing or obfuscating any other data on the device, but who knows — it may very well be that the Google Tensor’s CPU parts are the only thing they care about hiding.

Assuming the output wasn’t tampered with, we’ve determined that the Google Tensor will have the following CPU configuration:

• 2x ARM Cortex-X1 clocked at 2.802GHz
• 2x ARM Cortex-A76 clocked at 2.253GHz
• 4x ARM Cortex-A55 clocked at 1.80GHz

AnandTech‘s Andrei thinks the use of dual X1 cores is sensible, but he, as well as others we’ve spoken to, are perplexed by the apparent use of dual A76 cores. The Cortex-A76 was announced back in mid-2018 and has been succeeded by the A77 and more recently the A78, which is significantly better in terms of power, performance, and area (PPA). It’s hard for us to rationalize why Google may have chosen to go with two A76 cores instead of two A78 cores when there’s very little apparent benefit in doing so. We even checked the cpuinfo output from various Qualcomm and Exynos devices just to make sure the results were as expected and that we weren’t misinterpreting the output from the Pixel 6 Pro. We’d love to be proven wrong on this claim, but there’s no doubt that this CPU configuration is what the cpuinfo output from a real Pixel 6 Pro device suggests.

One important detail we don’t know about is the amount of cache available to the CPU cores. A large cache is quite important for the cores to reach the performance that Arm claims they can.

Furthermore, we still don’t know the number of GPU cores, which is difficult to find as that information isn’t readily exposed to the system. We previously learned that the Pixel 6 will have the same GPU design as the Exynos Galaxy S21 — the ARM Mali-G78 — a fact that we can corroborate through the real hardware. The GPU may be clocked at up to 848MHz, though without knowing the number of cores, we don’t know how well the phone will perform in comparison to other devices with this GPU.

ARM Mali-G78

In our previous report, we confirmed that the Google Tensor includes the “g5123b” modem, which very likely refers to Samsung’s Exynos 5123 modem. We also reported that the phone supports Wi-Fi 6E (ie. 6GHz Wi-Fi), has a Tensor Processing Unit (TPU) code-named “abrolhos” clocked at up to 1.230GHz, will be paired with a 12GB LPDDR5 RAM module, and will also feature at least one storage variant with 128GB of UFS storage. The phone will also have an UWB radio for short-range location tracking and digital car key support, among other features.

AV1 decode, other new tidbits

The Pixel 6 Pro ships with Google’s AV1 decoder (c2.google.av1.decoder), which is hardware-accelerated by the Google Tensor chip. The device can decode AV1 content at up to 4K resolution and 60fps. It can also decode HEVC content at up to 4K resolution and 120fps, or 8K resolution and 30fps. In comparison, the Samsung Exynos 2100 can decode AV1 content at up to 8K resolution and 30fps, or HEVC content at 8K resolution and 60fps. Still, the fact that the Google Tensor chip supports hardware-accelerated AV1 decoding at all is significant, as thus far all Qualcomm Snapdragon chips — and, by extension, Google’s past Pixel phones — have not supported that feature.

That Google chose to include HW AV1 decoding in its own Google Tensor chip shouldn’t come as a surprise, seeing as how the company has been one of the biggest proponents of the royalty-free video codec. The company’s push to require AV1 support was one of the primary grievances cited by Roku when it removed the YouTube TV app from its platform.

Speaking of codecs, our source confirmed to us that the Pixel 6 Pro supports both the aptX and aptX HD codecs, two Bluetooth audio codecs used by many wireless headsets on the market. These codecs must be licensed from Qualcomm, so some of our readers were concerned the Pixel 6 series wouldn’t support them since they don’t have Snapdragon chips. A Snapdragon chip is not required to support aptX, though, so these concerns were mostly baseless. However, it’s still good to confirm the Pixel 6 series will support high-quality Bluetooth audio. Sony’s LDAC is also supported.

Lastly, our source confirmed something we already suspected: There’s no video output on the Pixel 6 Pro. Google has, once again, opted to not implement DisplayPort Alternate Mode, which allows a DP video signal to be sent over the USB-C port. Android has had a barebones desktop mode for a few releases now, but Google seems to want nothing to do with it. That’s unfortunate because phones are more than powerful enough to handle day-to-day tasks for the average user, and with 12GB of RAM, the Pixel 6 Pro can easily handle all your multitasking needs.

The post Exclusive: Here are the likely specs of the Google Tensor chip in the Pixel 6 appeared first on xda-developers.

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