The GPU

Tegra 4 features an evolved GPU core compared to Tegra 3. The architecture retains a fixed division between pixel and vertex shader hardware, making it the only modern mobile GPU architecture not to adopt a unified shader model.

I already described a lot of what makes the Tegra 4 GPU different in our original article on the topic. The diagram below gives you an idea of how the pixel and vertex shader hardware grew over the past 3 generations:


We finally have a competitive GPU architecture from NVIDIA. It’s hardly industry leading in terms of specs, but there’s a good amount of the 80mm^2 die dedicated towards pixel and vertex shading hardware. There's also a new L2 texture cache that helps improve overall bandwidth efficiency.

The big omission here is the lack of full OpenGL ES 3.0 support. NVIDIA’s pixel shader hardware remains FP24, while the ES 3.0 spec requires full FP32 support for both pixel and vertex shaders. NVIDIA also lacks ETC and FP texture support, although some features of ES 3.0 are implemented (e.g. Multiple Render Targets).

Mobile SoC GPU Comparison
  GeForce ULP (2012) PowerVR SGX 543MP2 PowerVR SGX 543MP4 PowerVR SGX 544MP3 PowerVR SGX 554MP4 GeForce ULP (2013)
Used In Tegra 3 A5 A5X Exynos 5 Octa A6X Tegra 4
SIMD Name core USSE2 USSE2 USSE2 USSE2 core
# of SIMDs 3 8 16 12 32 18
MADs per SIMD 4 4 4 4 4 4
Total MADs 12 32 64 48 128 72
GFLOPS @ Shipping Frequency 12.4 GFLOPS 16.0 GFLOPS 32.0 GFLOPS 51.1 GFLOPS 71.6 GFLOPS 74.8 GFLOPS

For users today, the lack of OpenGL ES 3.0 support likely doesn’t matter - but it’ll matter more in a year or two when game developers start using OpenGL ES 3.0. NVIDIA is fully capable of building an OpenGL ES 3.0 enabled GPU, and I suspect the resistance here boils down to wanting to win performance comparisons today without making die size any larger than it needs to be. Remembering back to the earlier discussion about NVIDIA’s cost position in the market, this decision makes sense from NVIDIA’s stance although it’s not great for the industry as a whole.

Tegra 4i retains the same base GPU architecture as Tegra 4, but dramatically cuts down on hardware. NVIDIA goes from 4 down to 3 vertex units, and moves to two larger pixel shader units (increasing the ratio of compute to texture hardware in the T4i GPU). The max T4i GPU clock drops a bit down to 660MHz, but that still gives it substantially more performance than NVIDIA’s Tegra 3.

Memory Interface

The first three generations of Tegra SoCs had an embarrassingly small amount of memory bandwidth, at least compared to Apple, Samsung and Qualcomm. Admittedly, Samsung and Qualcomm were late adopters of a dual-channel memory interface, but they still got there much quicker than NVIDIA did.

With Tegra 4, complaints about memory bandwidth can finally be thrown out the window. The Tegra 4 SoC features two 32-bit LPDDR3 memory interfaces, bringing it up to par with the competition. The current max data rate supported by Tegra 4’s memory interfaces is 1866MHz, but that may go up in the future.

Tegra 4 won’t ship in a PoP (package-on-package) configuration and will have to be paired with external DRAM. This will limit Tegra 4 to larger devices, but it should still be able to fit in a phone.

Unfortunately, Tegra 4i only has a single channel LPDDR3 memory interface. Tegra 4i on the other hand will be available in PoP as well as discrete configurations. The PoP configuration may top out at LPDDR3-1600, while the discrete version can scale up to 1866MHz and beyond.

Round Two, Still Quad-Core Tegra 4 Performance
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  • Krysto - Monday, February 25, 2013 - link

    S600 is just a slightly overclocked S4 Pro with the same GPU.

    The real competitor of Tegra 4 will be S800. We'll see if it wins in CPU performance (it might not), and I think there's a high chance it will lose in GPU performance, as Adreno 330 is only 50% faster than Adreno 320 I think, and Tegra 4 is about twice as fast.

    Qualcomm has always had slower graphics performance than Nvidia actually. The only "gap" they found in the market was last fall with the Adreno 320, when Nvidia didn't have anything good to show. But Tegra 3 beat S4 with its Adreno 225.
    Reply
  • watersb - Monday, February 25, 2013 - link

    I'm amazed at the depth of this NVIDIA data-dump. Brilliant work.

    Anand's observation re: die size, cost strategy, position in the market and how this buys them time to consolidate... Wow.

    Clearly, Nvidia is in this game for the long haul.
    Reply
  • djgandy - Monday, February 25, 2013 - link

    So OpenGL ES 3.0 doesn't matter, but quad core A15 does? Why do people suck up to Nvidia and their marketing BS so much?

    T4i still single channel memory? What a joke configuration.
    Reply
  • djgandy - Monday, February 25, 2013 - link

    Also a 9 page article about a mobile SoC without a single reference to the word "battery". Reply
  • varad - Monday, February 25, 2013 - link

    Read the article before you write such comments. The very first page is "Introduction & Power" where they do mention some numbers and their thoughts. Reply
  • djgandy - Tuesday, February 26, 2013 - link

    Yeah its all smoke and mirrors under lab test conditions. Where is the real battery life? Is this not for battery powered devices? Reply
  • Krysto - Monday, February 25, 2013 - link

    Personally, I think all 2013 GPU's should have support for OpenGL ES 3.0 and OpenCL. I was stunned to find out Tegra 4 was not going to support it as they haven't even switched to a unified shader architecture.

    That being said, Anand is probably right that it was the right move for Nvidia, and they are just going to wait for the Maxwell architecture to streamline the same custom ARMv8 CPU from Tegra 5 to Project Denver across product line-ups, and also the same Maxwell GPU cores.

    If that's indeed their plan, then switching Tegra 4 to Kepler this year, only to switch again to Maxwell next year wouldn't have made any sense. GPU architectures barely change even every 2-3 years, let alone 1 year. It wouldn't have been cost effective for them.

    I do hope they aren't going to delay the transition again with Tegra 5 though, and I also do hope they follow Qualcomm's strategy with S4 last year of switching IMEMDIATELY to the 20nm process, instead of continuing on 28nm with Tegra 5, like they did with Tegra 3 on 40nm. But I fear Nvidia will repeat the same mistake.

    If they put Tegra 5 on 20nm, and make it 120mm2 in size, with Maxwell GPU core, I don't think even Apple's A8X will stand against it next year in terms of GPU performance (and of course it will get beaten easily in CPU performance, just like this year).
    Reply
  • djgandy - Tuesday, February 26, 2013 - link

    Tegra is smaller because it lacks features and also memory bandwidth. The comparison is not really fair to assume you can just throw more shaders at the problem. You'll need wider memory bus for a start. You'll need more TMU's and in the future it's probably smart to have a dedicate ROP unit. Then also are you seriously going to just stick with FP20 and not support ES 3.0 and OpenCL? OEMs see OpenCL as a de facto feature these days, not because it is widely used but because it opens up future possibilities. Nvidia has simply designed an SoC for gaming here.

    Your post focuses on performance, but these are battery powered devices. The primary design goal is efficiency, and it would appear that is why apple went swift and not A15. A15 is just too damn power hungry, even for a tablet.
    Reply
  • metafor - Tuesday, February 26, 2013 - link

    If the silicon division of Apple were its own business, they'd be in the red. Very few silicon providers can afford to make 120mm^2 chips and still make a profit; let alone one with as little bargaining clout in the mobile space as nVidia.

    Numbers are great but at the end of the day, making money is what matters.
    Reply
  • milli - Monday, February 25, 2013 - link

    nVidia is trying hard but Tegra still isn't making them any money ... Reply

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