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Nvidia's Tegra 4 GPU: Doubling Down On Efficiency

Tegra 4i: A Chip Off The Old Block

Tegra 4 is being groomed for the tablet and superphone space, wielding 4+1 Cortex-A15 CPU cores, the full 72-shader GPU, and an optional i500 soft modem. Tegra 4i, on the other hand, is Nvidia’s smartphone-oriented solution, armed with 4+1 Cortex-A9 r4 cores, a 60-shader GPU, and the i500, integrated.

Although Tegra 4i’s CPU component is clearly different, its GPU is based on the same architecture as Tegra 4. Instead of six vertex units, you get three, totaling 12 MADs. Meanwhile, four pixel pipes narrow to two. Notice that the same number of MADs exist in the fragment pipe, though. Nvidia made a very conscious decision, based on today’s content, to emphasize complex shading rather than fill rate. Some of this has to do with the effects developers can achieve by leveraging shader horsepower.

Tegra 4i block diagram

However, as a phone-oriented device, Tegra 4i needs to make efficiency its priority, and Nvidia picked its ratios with a single-channel 32-bit memory interface in mind. Why just one channel, rather than two? First, a dual-channel design would have been hard to fit into Tegra 4i’s 12x12 mm package. Two channels would have adversely affected baseline power consumption as well. So, implementing one channel and then populating it with DDR3 running at up to 2,133 MT/s as much as doubles Tegra 3’s bandwidth without hurting idle efficiency.

It also helps to consider the devices these SoCs are designed for. Tablets like the Nexus 10 are pushing 2560x1600 resolutions, while some of the latest super-phones sport 1080p 5” displays. At two pixels per clock, a 660 MHz Tegra 4i does more than 1.3 Gpix/s. A 1080p phone with just over two million pixels, refreshing at 60 Hz, needs fewer than 125 million pixels per second. Tegra 4i gives you enough fill horsepower for more than 10x overdraw, filling every pixel on the screen. Hence, Nvidia thinks it effectively balanced resources given the platform it’s targeting with Tegra 4i.

  • s3anister
    I'm always amazed with the progress made in strides in this ultra-competitive sector so it's nice to see nvidia finally hit 28mm with Tegra 4. I'm sure some of their performance gains can be attributed to this.
    Reply
  • levin70
    Charlie at semiaccurate is correct. The Tegra 4 is DOA. Almost no one will be using it. Everyone else is already ahead of where the T4 is today, and it hasn't even launched. How many design wins were noted? 1?

    Yeah, says it all.
    Reply
  • Memnarchon
    A Sunday article? :O
    Reply
  • deedee2die4
    Nvidia staying on top, the best of the best!
    Reply
  • blazorthon
    deedee2die4Nvidia staying on top, the best of the best!
    Uhh, no... T4 isn't supposed to be out for like six months, yet it's already not as fast as some of Qualcomm's latest. Nvidia is improving, but as usual, they're staying a little behind in technology.
    Reply
  • aicom
    levin70Charlie at semiaccurate is correct. The Tegra 4 is DOA. Almost no one will be using it. Everyone else is already ahead of where the T4 is today, and it hasn't even launched. How many design wins were noted? 1?Yeah, says it all.Nobody is ahead of Tegra's four Cortex A15 cores. Krait is at less performance than A15 (until the refresh at least). Samsung's got Exynos 5 Octa, but that's not out yet either and T4 will probably still top it in the GPU performance department. Speaking of which, Tegra 4 has the most powerful GPU in floating-point of anyone (including the iPad 4) with 74.8 TFLOPS @ 672 MHz. It only takes a 825 MHz Cortex A15 to match a 1.6 GHz A9, and Tegra 4 is supposed to ship at 1.9 GHz. Unfortunately, TDP does go up in the process.

    You also have to look at where these parts are targeted. Krait is really gunning for phone design wins and they have many. It's a very power efficient chip that found its way into some very nice phones. Tegra 4 is not aimed at that market; Tegra 4i is. Tegra 4 will have a much higher TDP than 4i (and Krait) and will get substantially higher performance as a result.
    Reply
  • tjosborne
    Hey guys, I am considering getting a Asus transformer prime tablet with the tegra 3. Would it be best to wait till this processor ends up in a tablet to get one?
    Reply
  • So at 1.3Gpix/s, Nvidia has just admitted to 10x overdraw...per second? So we're looking at 9~10 frames per second oh high res displays. Lag lives on.
    Reply
  • PreferLinux
    aicomNobody is ahead of Tegra's four Cortex A15 cores. Krait is at less performance than A15 (until the refresh at least). Samsung's got Exynos 5 Octa, but that's not out yet either and T4 will probably still top it in the GPU performance department. Speaking of which, Tegra 4 has the most powerful GPU in floating-point of anyone (including the iPad 4) with 74.8 TFLOPS @ 672 MHz. It only takes a 825 MHz Cortex A15 to match a 1.6 GHz A9, and Tegra 4 is supposed to ship at 1.9 GHz. Unfortunately, TDP does go up in the process.You also have to look at where these parts are targeted. Krait is really gunning for phone design wins and they have many. It's a very power efficient chip that found its way into some very nice phones. Tegra 4 is not aimed at that market; Tegra 4i is. Tegra 4 will have a much higher TDP than 4i (and Krait) and will get substantially higher performance as a result.You mean Gigaflops, not Teraflops.
    Reply
  • blazorthon
    aicomNobody is ahead of Tegra's four Cortex A15 cores. Krait is at less performance than A15 (until the refresh at least). Samsung's got Exynos 5 Octa, but that's not out yet either and T4 will probably still top it in the GPU performance department. Speaking of which, Tegra 4 has the most powerful GPU in floating-point of anyone (including the iPad 4) with 74.8 TFLOPS @ 672 MHz. It only takes a 825 MHz Cortex A15 to match a 1.6 GHz A9, and Tegra 4 is supposed to ship at 1.9 GHz. Unfortunately, TDP does go up in the process.You also have to look at where these parts are targeted. Krait is really gunning for phone design wins and they have many. It's a very power efficient chip that found its way into some very nice phones. Tegra 4 is not aimed at that market; Tegra 4i is. Tegra 4 will have a much higher TDP than 4i (and Krait) and will get substantially higher performance as a result.
    S4 Pro is a faster CPU IIRC. IDK about how the graphics compares and won't comment about it.

    Nvidia, like I said, is getting better, but they're still going to be a little behind. They're making up a lot of ground here, especially with how they're making Tegra 4 and Tegra 4i instead of a single SoC to take both places, but they seem like they'l still have a little room to make up, at least in CPU performance, to be the best. Like I said before (at least in other articles about it), they'll still be near the top either way.
    Reply