The iPhone Becomes a Gaming Platform: Enter the PowerVR SGX

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.

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.

Enter the ARM Cortex A8 Final Words: Preparing for 3GS
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  • Anand Lal Shimpi - Wednesday, June 10, 2009 - link

    In addition to the ARM11 core, I believe the GPU side of tegra does use too much power for something like the iPhone. I can't find detailed specs for NVIDIA's low end Tegra, but Wikipedia lists ~4W for the higher end model - that's simply too much. We need to see values in the mW range.

    Take care,
    Anand
    Reply
  • peccavi - Wednesday, June 10, 2009 - link

    From what I gathered, Apple is increasing support for iPhone peripherals. Could this allow for a controller / docking cradle for the iPhone? Imagine 4 buttons and a couple of directional pads on either end of the phone in landscape mode. Would make for a great little gaming unit. Reply
  • eburnette - Wednesday, June 10, 2009 - link

    One thing that wasn't clear from the article is how certain are you about the information? Is it just speculation at this point until somebody gets one and tears it down? Reply
  • Anand Lal Shimpi - Wednesday, June 10, 2009 - link

    I'm very certain. The info comes from sources very close to the licensees for both the CPU and GPU. Without hardware in hand it's impossible to be 100% sure, but what Apple has implied lines up well with what I've been told.

    The ~2x gains in app performance would only come from a faster processor. Apple's options there are to either use a much higher clocked ARM11 or move to the Cortex A8. You can't get 2x out of a 200MHz speed boost to an ARM11 core, so that leaves the A8.

    The graphics side I'm also very sure about, although I can't post why :)

    Take care,
    Anand
    Reply
  • psychobriggsy - Wednesday, June 10, 2009 - link

    Thanks for confirming the rumours.

    I think you should point out that the CPU and GPU are actually on the same die, indeed everything apart from the RAM will be on that die. Some parts of the article imply that the CPU and GPU simply share the package, but could be separate dies.

    A little sad that the GPU is the SGX520 - the lowest end, but it's still so much better than the MBX it doesn't matter. Shame you can't snaffle a die shot from Samsung ;) maybe the graphics are by comparison quite large, even considering the A8 with L2 cache.

    The crypto co-processor that's been added is certainly being used, as hardware crypto was mentioned in the keynote. That will aid iPhone SSL web browsing speed I'd hope.

    Also the A9 is out-of-order, so comparable to a Nano, as the A8 is comparable to Atom and the ARM11 is comparable to a very fast 486.
    Reply
  • Simon F - Wednesday, June 10, 2009 - link

    [quote]Paired with this CPU is a PowerVR MBX-Lite GPU core. This GPU, like the CPU, is built on a 90nm process and is quite simple. The GPU does support hardware transform and lighting but it’s fully fixed function, think of it as a DirectX 6/7 class GPU (Riva TNT2/GeForce 256).[/quote]

    This is not strictly correct. IIRC the MBX model in the iPhone has a programmable vertex shader that exceeds DX8. The pixel pipeline, though, is fixed function. Having said this, I'm not sure if the programmable aspects of the vertex shader are exposed in the iPhone interface.
    Reply
  • faxon - Wednesday, June 10, 2009 - link

    i have by and large stayed away from apple my entire life, but given their recent innovation on the consumer devices front and their virtual monopoly on the high capacity music players market with the ipod, i have been keeping them on my radar none the less. when a family member picked up an iphone3G when we switched to AT&T for our wireless service, i was actually rather impressed at simply how much better it was than the blackjack 2 i picked up, at just about everything. the only complaint i had was in its texting performance, but with a cloned SIM card i could get around that simply by pulling out my blackjack 2 instead. I have been looking at getting an iphone since i use my phone for mobile browsing excessively, and even using opera the blackjack 2 doesnt come close in ease of use compared to the old iphone on edge. with the new 3Gs also supporting picture texting (a requirement of my GF) i may just look into this if i get the promotion im gaming for by the end of the summer. Reply
  • sxr7171 - Wednesday, June 10, 2009 - link

    I avoided the iPhone for so long and I even bought one to jailbreak and play with, but it wasn't until OS 3.0 that it became my daily phone. The Exchange support on it beats most other smartphones. Reply
  • strikeback03 - Wednesday, June 10, 2009 - link

    I'd say high capacity music players are the only segment of mp3 players where the Ipods are not dominant. The only high capacity models are the classic/video ones, which don't seem to be that popular and don't appear to have been upgraded nearly as recently as the touch and nano. Reply
  • Dennis Travis - Wednesday, June 10, 2009 - link

    Anand, thanks so much for your preview. I can't wait for your review after you get a hold of the phone. I am really interested in battery life. During the keynote I thought they said something about a new battery and that was why more battery life. I guess we will soon know for sure.

    Thanks again!
    Reply

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