The GPU and its Performance

We’ve gone through, in great depth, the CPU in the new iPhone 3GS. But the GPU is arguably the more interesting upgrade. I’ve already covered the GPU pretty well so I present you with a blatant copy/paste of what I’d already written:

Now that we’re familiar with the 3GS’ CPU, it’s time to talk about the GPU: the PowerVR SGX.

Those familiar with graphics evolution in the PC space may remember Imagination Technologies and its PowerVR brand by their most popular desktop graphics card: STMicro’s Kyro and Kyro II. The Kyro series used the PowerVR3 chips and while STMicro ultimately failed to cement itself as a NVIDIA competitor in the desktop, the PowerVR technology lived on in ultra-mobile devices.

The SGX is on Imagination Technologies’ fifth generation of its PowerVR architecture, and just like the Kyro cards we loved, the SGX uses a tile based renderer. The idea behind a tile or deferred renderer is to render only what the camera sees, not wasting clocks and memory bandwidth on determining the color of pixels hidden by another object in the scene. Tile based renderers get their name from dividing the screen up into smaller blocks, or tiles, and working on each one independently. The smaller the tile, the easier it is to work on the tile on-chip without going to main memory. This approach is particularly important in the mobile space because there simply isn’t much available bandwidth or power. These chips consume milliwatts, efficiency is key.

The MBX-Lite used in the original iPhone was also a tile based architecture, the SGX is just better.

Also built on a 65nm process the PowerVR SGX is a fully programmable core, much like our desktop DX8/DX9 GPUs. While the MBX only supported OpenGL ES 1.0, you get 2.0 support from the SGX. The architecture also looks much more like a modern GPU:

Pixel, vertex and geometry instructions are executed by a programmable shader engine, which Imagination calls its Universal Scalable Shader Engine (USSE). The “coprocessor” hardware at the end of the pipeline is most likely fixed-function or scalar hardware that’s aids the engine.

The SGX ranges from the PowerVR SGX 520 which only has one USSE pipe to the high end SGX 543MP16 which has 64 USSE2 pipes (4 USSE2 pipes per core x 16 cores). The iPhone 3GS, I believe, uses the 520 - the lowest end of the new product offering. Update: Thanks to BlazingDragon and psonice for pointing out that the 3GS may in fact use a PowerVR SGX 535 based on drivers on the iPhone 3GS. It could still use a lower end SGX core and use the 535's driver, but there's at least the possibility that the 535 is under the hood of the 3GS.

A single USSE pipe can execute, in a single clock, a two-component vector operation or a 2 or 4-way SIMD operation for scalars. The USSE2 pipes are upgraded that handle single clock 3 or 4 component vector operations, have wider SIMD and can co-issue vector and scalar ops. The USSE2 pipes are definitely heavier and have some added benefits for OpenCL. For the 3GS, all we have to worry about is the single USSE configuration.

  iPhone 3G (PowerVR MBX-Lite) PowerVR SGX @ 100MHz PowerVR SGX @ 200MHz
Manufacturing Process 90nm 65nm 65nm
Clock Speed ~60MHz 100MHz 200MHz
Triangles/sec 1M 3.5M 7M
Pixels/sec 100M 125M 250M

 

In its lowest end configuration with only one USSE pipe running at 200MHz, the SGX can push through 7M triangles per second and render 250M pixels per second. That’s 7x the geometry throughput of the iPhone 3G and 2.5x the fill rate. Even if the SGX ran at half that speed, we’d still be at 3.5x the geometry performance of the iPhone 3G and a 25% increase in fill rate. Given the 65nm manufacturing process, I’d expect higher clock speeds than what was possible on the MBX-Lite. Also note that these fill rates take into account the efficiency of the SGX’s tile based rendering engine.

Obviously all games on the app store were designed for the PowerVR MBX-Lite and the SoC in the iPhone/iPhone 3G/iPod Touch. Some do run faster/smoother on the 3GS thanks to the faster CPU and GPU, but the new hardware should enable an entirely new class of game in the future.

Developers will have to deal with a segmented user base, since there are around 20 million PowerVR MBX-Lite based phones and a bit over 1 million SGX based 3GSes in the market.

The GPU Comparison

There are obvious limitations to the iPhone 3GS being used as a gaming platform. But there are also obvious limitations to the 3GS being used as a camera or a video player. The point isn’t that the 3GS could replace the Nintendo DS or the Sony PSP, it’s that the iPhone could get you maybe 80 - 90% of the way there.

There are serious control and battery life limitations, but the platform has the right combination of hardware, a software delivery system and ubiquity to at least be considered a viable gaming system. It has a much more powerful CPU/GPU combination than a Nintendo DS, now what it needs is the iPhone equivalent of Mario. Perhaps Apple should buy a game developer.

The obvious smartphone GPU comparison here is the Palm Pre. The TI OMAP 3430 used in the Pre (good job Palm on full disclosure there, just add clock speeds and you’ll get an A+) is a very similar SoC to the Samsung chip in the iPhone 3GS. As such, it also has a PowerVR SGX core.

The CPU and its Performance Camera and Video Capture
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  • psonice - Tuesday, July 7, 2009 - link

    My understanding is that the iphone 3gs GPU is actually a 535, not a 520. At least, this is the current understanding among iphone developers, and there's an SGX535 driver on the phone to support that. The extra power might explain the hit on battery life when playing games.

    Real numbers are pretty hard to come by, but it seems the 535 is roughly 4x faster than the 520. If so, that's a massive upgrade rather than just a decent one. The 535 also supports HD video decoding where the 520 doesn't - not that apple seem to be supporting it if it does.

    I heard too that the palm pre has a 530 GPU, which is 2x faster than the 520. That puts the iphone a long way ahead for graphics instead of behind.

    One thing in the article I really disagree with btw: you say that the phone makers should provide detailed specs. I think they shouldn't, as it's not helpful at all for the average buyer. If you go into a shop without having much clue and ask for an iphone because it's the latest thing, and the shop assistant says "well this is like an iphone, but it runs 200mhz faster" you'll end up buying the "better" phone based on the spec sheet, even if it's running win mobile 5.

    I was in Japan a while back, and they tend to buy phones based on the spec sheets there. The phones all compete on having the most features. They're all really big and HORRIBLE to actually use. None of that please!

    I think apple actually get their commercials right with the iphone on the whole: show somebody actually using the phone to do stuff. If the other manufacturers did the same, that would be a perfect way to compare.
    Reply
  • christinme7890 - Thursday, July 9, 2009 - link

    I agree with you holistically. There are not many people in this world that even understand the specs. Not to mention when it comes to specs, and the person has no clue, they end up getting the one with the highest numbers. This is bad. I think you are right in saying that the way apple works their commercials is perfect for people. They show people all the great apps that they could use and they say that ALL of these apps can be on one phone.

    This is why I hate the Best buy MS commercials where the kid goes into the BB and buys a PC instead of a mac. The person always buys the computer with the best specs and care little about the OS, which is what they will be using. Windows, imo after using a Mac for a year, sucks in comparison to Mac. I rarely have a problem with a mac. I sit in class everyday and watch all the pc people have startup errors and os sleep or hibernation errors. I can close my mac and KNOW WITHOUT A DOUBT that it will wake up totally fine. Not to mention it wakes up seamlessly without load screens or anything. I will not compare the two but for business and usability the MAC gets my vote and I think if Apple does their commercials for the macs just as great. Sure most people are still using MS but that is because MS strong arms people into buying their stuff everytime you buy a Computer (not to mention Apple is very strict with their software and rightly so).
    Reply
  • Anand Lal Shimpi - Tuesday, July 7, 2009 - link

    Ooh, very interesting - do you have any links to discussions on the 535 being in the 3GS?

    I don't think end users need to be bombarded with specs, but I think there needs to be more information put out about these things. We shouldn't have to play guessing games about clocks and specs; don't market them, but don't hide them either - that's my thinking.

    Take care,
    Anand
    Reply
  • BlazingDragon - Tuesday, July 7, 2009 - link

    Anand, here it is:
    http://www.macrumors.com/2009/06/25/iphone-3gs-has...">http://www.macrumors.com/2009/06/25/iph...has-more...
    Reply
  • Anand Lal Shimpi - Tuesday, July 7, 2009 - link

    Very interesting - thanks guys, I've updated the article.

    Take care,
    Anand
    Reply
  • ltcommanderdata - Tuesday, July 7, 2009 - link

    It should probably also be noted that the MBX-Lite supports OpenGL ES 1.1 as implemented by Apple not just OpenGL ES 1.0. I believe it's Android's implementation that currently only supports OpenGL ES 1.0.

    It's also been reported that the iPhone OS 3.1 betas include improvements to the OpenGL stack that include additional OpenGL extensions. Whether these are focused on OpenGL ES 2.0 and the SGX or are also for OpenGL ES 1.1 and the MBX remains to be seen. Although on the issue of reducing market segmentation, it'd be great if Apple could implement the OpenGL ES 1.1 Extension Pack although I don't know if the MBX-Lite can actually support it in hardware.
    Reply
  • BlazingDragon - Tuesday, July 7, 2009 - link

    Anand, here's it is:
    iPhone 3GS Has More Powerful PowerVR SGX 535 GPU?
    Reply
  • kelmerp - Tuesday, July 7, 2009 - link

    I'm trying to decide between the MyTouch or a jailbroken iphone. Reply
  • sxr7171 - Wednesday, July 8, 2009 - link

    JB iPhone vs. MyTouch? They're not even in the same league. Pre vs. iPhone is a comparison. Reply
  • pennyfan87 - Tuesday, July 7, 2009 - link

    anand,

    i love you writing and tech analysis.

    but please, drop the fanboyism.
    3 articles on such a minor upgrade? please.

    more SSD stuff please.
    Reply

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