In the past few years, we’ve seen NVIDIA shift their mobile strategy dramatically with time. With Tegra 2 and 3, we saw multiple design wins in the smartphone space, along with the tablet space. These SoCs often had dedicated GPUs that were quite unlike what we saw in NVIDIA’s desktop and laptop GPUs, with a reduced feature set and unique architecture. However, with Tegra K1 we saw a distinct shift in NVIDIA’s SoC strategy, as the Tegra K1 was the first mobile SoC to achieve parity in GPU architecture with desktop GPUs. In the case of the Tegra K1, this meant a single Kepler SMX which made for truly incredible GPU performance. However, in the time since we’ve seen companies like Apple release new SoCs such as the A8X, which managed to bring largely similar performance with less power.

NVIDIA of course is never content to stay idle for too long and let themselves be surpassed, which has led to the company developing their Tegra SoCs on a roughly yearly cadence. In NVIDIA’s development timeline, 2014 brought us the Tegra K1-32, the company’s first SoC to integrate a modern high-performance GPU architecture (Kepler), and later on the TK1-64, a K1 with NVIDIA’s own in-house developed ARMv8 Denver CPU in place of the 32bit ARM A15 CPU.


NVIDIA's GTC 2014 Tegra Roadmap

2014 also brought a revision to NVIDIA’s public Tegra roadmap: for 2015 NVIDIA would bump the previously announced Parker SoC and release a new in its place, Erista. This schedule change ended up being quite a surprise due to the fact that NVIDIA had up until this time released their roadmaps roughly 2 years out, whereas Erista was put on the map less than a year before it was to be announced. More unusual, NVIDIA offered up minimal details of Erista; it would be powered by a Maxwell GPU with no additional information on the CPU or manufacturing process. Parker on the other hand – NVIDIA’s planned Denver + Maxwell + 16nm FinFet part – fell off the schedule, with NVIDIA not officially canceling it but also saying little else about it.

Now in 2015 and with the launch of the Tegra X1, we can finally begin putting the picture together. Erista as it turns out is something of a rapid release product for NVIDIA; what had been plans to produce a 16nm FF part in 2015 became plans to produce a 20nm part, with Erista to be that part. To pull together Erista NVIDIA would go for a quick time-to-market approach in SoC design, pairing up a Maxwell GPU with ARM Cortex A57 & A53 GPUs, to be produced on TSMC’s 20nm SoC process.

CPU

We’ll kick off our look at Erista then with a look at Erista’s CPUs, where one of the bigger surprises in Erista is the CPU configuration. While Tegra K1 had a version with NVIDIA’s custom Denver core for the CPU, NVIDIA has elected to use ARM’s Cortex A57 and A53 in the Tegra X1. The A57 CPU cluster has 2MB of L2 cache shared across the four cores, with 48KB/32KB L1s (I$+D$) per core. The A53 cluster has 512KB of L2 cache shared by all four cores and 32KB/32KB L1s (I$+D$) per core. NVIDIA representatives stated that this was done for time to market reasons.

However, rather than a somewhat standard big.LITTLE configuration as one might expect, NVIDIA continues to use their own unique system. This includes a custom interconnect rather than ARM’s CCI-400, and cluster migration rather than global task scheduling which exposes all eight cores to userspace applications. It’s important to note that NVIDIA’s solution is cache coherent, so this system won't suffer from the power/performance penalties that one might expect given experience with previous SoCs that use cluster migration.

Although cluster migration is usually a detriment to power and performance (especially without a cache coherent interconnect), NVIDIA claims that Tegra X1 significantly outperforms Samsung System LSI’s Exynos 5433 in performance per watt with 1.4x more performance at the same amount of power or half the power for the same performance on the CPU. It's likely that this difference comes from optimizing the implemented logic and differences between Samsung and TSMC 20nm processes rather than differences in thread management. NVIDIA continues to use System EDP (Electrical Design Point) management to control throttling and turbo rather than ARM's IPA (Intelligent Power Allocation) drivers, and in general it seems that while the CPU architecture is ARM's reference design it's quite clear that everything else is distinctly NVIDIA in design.

All of this of course raises the question of where’s Denver, and what is to happen to it? The use of the ARM Cortex A57 and A53, as NVIDIA tells it, was based on a time-to-market decision, and that NVIDIA could bring an off-the-shelf Cortex-based SoC to the market sooner than they could another Denver SoC. On the surface there is at least some evidence to agree with this, as NVIDIA would be able to buy a 20nm design from ARM versus spending the time porting Denver over from TSMC’s 28nm process to their 20nm process. At the same time however integrating an ARM CPU core into an SoC is not an easy task – logic LEGO this is not – so it’s hard to say whether this actually saved NVIDIA much time.  

In any case, much like the still in the dark Parker design, NVIDIA is holding their cards close to their chest and hinting that Denver will still be in future generation products. If Parker is still part of NVIDIA’s plans – and they are without a doubt working on some kind of 16nm FF Tegra SoC – then we may still see Denver as part of the original Parker plan. Otherwise at this point while there’s no reason not to believe NVIDIA about the fate of future Denver SoCs, it’s anyone’s guess when we might see it again.

Uncore

Outside of the CPU and GPU, NVIDIA has also dramatically improved the rest of Tegra X1 in comparison with Tegra K1. We see a move from 64-bit wide LPDDR3 to 64-bit wide LPDDR4 on the memory interface, which improves peak memory bandwidth from 14.9 GB/s to 25.6 GB/s and improves power efficiency by around 40%. In addition, the maximum internal display resolution moves from 3200x2000 at 60 Hz to 3840x2160 at 60 Hz with support for VESA’s display stream compression. For external displays, we see a significant improvement with support for HDMI 2.0 and HDCP 2.2, which means that 4K60 is supported in contrast with the Tegra K1, which only supported 4K30.

The ISP is largely similar to the one we see in the Tegra K1 when it comes to feature set, but JPEG encode and decode rate is now five times as fast, going from 120 MP/s to 600 MP/s. For video encode and decode, we see support for 4K60 H.265 and VP9, with support for 10 bit color on decode on H.265. In addition to support for new codecs in the hardware blocks, we see that H.264 and VP8 now support 4K60, a notable improvement over the 4K30 that was the maximum for Tegra K1. We also see that the storage controller now supports eMMC 5.1 for faster storage performance.

Tegra X1's GPU: Maxwell for Mobile
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  • SM123456 - Sunday, February 01, 2015 - link

    >>He was saying: why NV didn't continue with Denver design? Being so efficient and only 2 cores why don't shift at 20nn easily? Because they can't and that's it. The other things are speculations.<<

    There is a simple answer to that - Apple has booked all the production slots for 20nm (made by foundry TSMC) to meet demand for the A8. This has pushed back production of the 16nm to late 2015. That is the reason for the delay in Denver, which nVidia originally intended for the Tegra K1 Denver successor, the Pascal chip. That is the reason for the delay in Pascal.

    20nm is a risk reducing interim technology which almost everybody is skipping. Apple originally wanted 14/16nm for the A8, only used 20nm because they couldn't wait to release the current iPhone on 14/16nm. nVidia is only producing the Tegra X1 at 20nm because they are worried about the same problem happening at 16nm. With 20nm, they know that Apple will be moving off 20nm with the next iPhone, so there will definitely be spare production capacity.
    Reply
  • utferris - Monday, April 13, 2015 - link

    I can not agree you any more. They aliens can not be reasonable. Reply
  • GC2:CS - Wednesday, January 07, 2015 - link

    2) I could make 4 cluster A7 GPU faster than tegra K1 and I could make a 16 cluster series 7XT GPU that's slower than tegra K1.

    So tell me how the heck does the number of clusters or "cores" relates to efficiency ???
    Reply
  • lucam - Wednesday, January 07, 2015 - link

    Since you re so expert about Imagt cluster you can explain why there some model of G6230 - 2 clusters (Allwinner socs) fast as much as an A7 (G6430) - 4 clusters. Maybe because the former has clock frequency higher than latter? But are pretty much the same in term of performance/watt....there we go.. Reply
  • SM123456 - Sunday, February 01, 2015 - link

    Errr.. same performance and price per watt for Apple on 20nm as nVidia at 28nm? That is damning. Reply
  • SM123456 - Sunday, February 01, 2015 - link

    The cores aren't important, the performance is. That is the whole point. The responsiveness depends on single core performance and to a lesser extent two core performance, and on this point Denver beats the crap out of the Apple A8 and A8X. Therefore the fact that Apple added an extra core to the A8 to get A8X is about benchmark bragging rights, and the A8X real world performance (based on single and dual core performance) lags the Tegra K1 Denver even with A8X on 20nm and Denver K1 on 28nm - not good for Apple.
    Reply
  • lucam - Tuesday, January 06, 2015 - link

    The Tegra speculations of chizow are priceless! Reply
  • aenews - Saturday, January 24, 2015 - link

    The K1 is four months or so older than the A8X. It crushed every chip very badly for four whole months. If anything, everyone else was/is playing catchup. And not to mention the Snapdragon 810, yet to be released, does not even come close to the K1 despite being a year newer. Reply
  • utferris - Monday, April 13, 2015 - link

    > "The K1 is four months or so older than the A8X."
    How do you come up with that?
    A8X was in production way before K1.
    It is just you see A8X only on ipad, when NVidia is showing off all around the test board that does not actually in production.
    Reply
  • chizow - Monday, January 05, 2015 - link

    @Mayuyu; I wouldn't be surprised if this is the final outcome of the Nvidia IP Patent lawsuits and why Apple was excluded from the original litigation. My bet is they (Apple) have already engaged in serious talks with Nvidia and they are both just awaiting a favorable outcome against Samsung/Qualcomm before moving forward. Reply

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