Enter the ARM Cortex A8

This past weekend Palm introduced its highly anticipated Pre. While I’m still working on my review of the Pre, I can say that it’s the closest thing to an iPhone since Apple first unveiled the product two summers ago. In many ways the Pre is lacking in areas that the iPhone has honestly perfected, but in others the Pre easily surpasses Apple’s best.

One such area is raw performance. While both the iPhone and iPhone 3G use the same old CPU/GPU, the Pre uses TI’s OMAP 3430 processor. The 3430, like the SoC Apple uses, has both a CPU and GPU on the same package. Instead of the ARM11 and the PowerVR MBX-Lite however, the OMAP 3430 uses an ARM Cortex A8 core and a PowerVR SGX GPU. Both are significant improvements over what was in the original iPhone.

Thankfully, Apple fans don’t have to be outclassed for long - the newly announced iPhone 3GS uses a comparable CPU/GPU pair.

Although unannounced, the iPhone 3GS uses (again) a Samsung SoC but this time instead of the ARM11 + MBX-Lite combo it’s got a Cortex A8 and PowerVR SGX; just like the Pre.

A derivative of this is what you'll find in the iPhone 3GS

If the ARM11 is like a modern day 486 with a very high clock speed, the Cortex A8 is like a modern day Pentium. The A8 lengthens the integer pipeline to 13 stages, enabling its 600MHz clock speed (what I’m hearing the 3GS runs at). The Cortex A8 also widens the processor; the chip is now a two-issue in-order core, capable of fetching, decoding and executing two RISC instructions in parallel.

The ARM11 processor in the iPhone/iPhone 3G has a basic vector floating point unit, but the A8 adds a much more advanced SIMD engine called NEON. The A8 also has twice as many double precision FP registers as the ARM11. The addition of NEON and the improved vector FPU in the A8 makes the processor much less like the original Pentium and much more like Intel’s Atom. Granted, Atom is significantly faster than the A8, but it also draws much more power.

Caches also get a significant improvement. I believe Apple will be using a derivative of Samsung’s S5PC100, which has a 32KB/32KB L1 cache (I/D, we may see a 16KB/16KB config instead) and a 256KB L2 cache. The L2 cache, as you’ll remember from the first section, is a new addition to the A8; the ARM11 core didn’t have an L2.

  iPhone 3G (ARM11) iPhone 3GS (ARM Cortex A8)
Manufacturing Process 90nm 65nm
Architecture In-Order In-Order
Issue Width 1-issue 2-issue
Pipeline Depth 8-stage 13-stage
Clock Speed 412MHz 600MHz
L1 Cache Size 16KB I-Cache + 16KB D-Cache 32KB I-Cache + 32KB D-Cache
L2 Cache Size N/A 256KB


The combination of higher clock speeds, more cache and a dual-issue front end results in a much faster processor. Apple claims the real world performance of the iPhone 3GS can be up to 2x faster than the iPhone 3G, and I believe that’s quite feasible.

The new SoC is built on a 65nm manufacturing process, down from 90nm in the original hardware. However, power consumption should still be higher for the new SoC compared to the old one. ARM’s own site lists ~0.25mW per MHz for the ARM11 core but < 0.59mW per MHz for the A8. That’s for a 650MHz low power A8 core and I’m expecting 600MHz for the 3GS, that’s at most 3x the power consumption of the CPU in the original iPhone. So how can Apple promise better battery life?

The thing about these comparisons is that they don’t show the full picture. With the same battery capacity, running at full speed, the new iPhone 3GS would run out of juice faster than the existing iPhone 3G. But that’s rarely how people use their phones. Chances are that you’ll perform a few tasks before putting the phone back to sleep, and what matters then is how quickly you can complete those tasks.

Just under nine years ago Intel talked about a technology called Quick Start. Let me quote from our IDF 2000 Day 2 coverage (wow, that was a while ago):

“"Intel has figured out that it is best to use full CPU power for a split second to finish a task and then put the CPU to idle as this conserves battery life the best. Although one may suspect that when running complex operations the CPU would not have time to go idle, this is not the case. To illustrate this point, Intel used an example of DVD playback. Very stressful on the system as a whole, Intel's quick start technology allows the CPU to "hurry up" and perform the DVD decoding operations and then go idle until the frame is displayed to screen and the next scene needs to be calculated. This saves battery life because, although the system may require 3 watts or so to "hurry up", the power consumption goes down near .25 watts when idle. By averaging these two numbers, one can quickly see how quick start can extend battery life."”

The A8’s power consumption has to be well under that 3x max I quoted above, and the iPhone 3GS needs to be more than just 2x faster at executing instructions, but if possible then it’s quite feasible for the faster A8 to draw more instantaneous power but draw less power on average than the ARM11 core in the original iPhone.

Index The iPhone Becomes a Gaming Platform: Enter the PowerVR SGX
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  • sxr7171 - Wednesday, June 10, 2009 - link

    A Dreamcast in the palm of your hand. Please port some Dreamcast titles to this phone. I would order mine this minute.
  • squngy - Wednesday, June 10, 2009 - link

    So how would these systems compare with the PSP or DS?

    If we're talking about games, then it would make sense to know where it stands compered to other popular gaming devices.
  • Anand Lal Shimpi - Wednesday, June 10, 2009 - link

    Compared to the DS, the iPhone 3G (and 3GS) are both way more powerful. That thing uses an ARM9E based processor and runs at no more than 133MHz I believe. The Cortex A8 should run circles around it. According to Wikipedia, the DS' "GPU" can reach a peak of 120K triangles per second...the first iPhone is capable of 1M per second. The iPhone is a superior hardware platform from a specs standpoint.

    The PSP is a bit more difficult of a comparison. It's got two MIPS cores plus a GPU. I haven't looked deeply into its architecture but I believe the 3GS should still be faster.

    Memory size is a huge limiting factor. The PSP has 2MB of video memory, 32MB of application memory and 4MB of embedded DRAM? The DS is even worse, it only has 4MB of RAM and < 1MB of video memory!

    The original iPhone had, what, 128MB? Everyone is expecting 256MB from the next-generation model.

    It's only a matter of time before handheld consoles are replaced by something like the iPhone. Console makers have to subsidize the cost of their hardware across games, cellular providers already subsidize the hardware costs of smartphones. There's huge potential here.

    Take care,
  • Anand Lal Shimpi - Thursday, June 11, 2009 - link

    Update - digging more into the PSP specs it's quite possible that the PSP is a faster gaming platform. It's difficult comparing CPUs since we're talking about a cross-architecture comparison, but on the GPU side the PSP appears to have more raw power. How that translates into real world performance compared to the PowerVR SGX in the 3GS remains to be seen. The 3GS most definitely has an efficient core.

    The memory comparison is still valid, especially with the 3GS at 256MB of RAM things get even more interesting.

    Take care,
  • Jovec - Wednesday, June 10, 2009 - link

    Wireless companies don't subsidize anything - they simply have an absolutely huge markup that then can then discount you $50 or $100 with a contract.
  • ViRGE - Wednesday, June 10, 2009 - link

    Depending on whether we're talking about the DS or the DSi, the main CPU is 66mhz or 133mhz respectively (always operating at 66mhz in DS mode). Both come with the ARM7 co-processor, which runs at 33mhz. The RAM value for the DS is right, meanwhile the DSi has 16MB. RAM's a bit iffy of course, the DS isn't running an operating system in the background and Slot-1 affords some in-place use of assets (albeit not true in-place execution like the GBA that let it get away with virtually no RAM). At any rate, the DS is still less powerful than the iPhone 3GS obviously.

    You're correct about the PSP, it has 2 MIPS processors (one for CPU use, one as a graphics processor) that can run between 22mhz and 333mhz. Most games for it are at 222mhz, a small number of titles push it to 333mhz. In raw CPU performance the 3GS is likely ahead, in GPU performance however it's entirely possible the PSP is still in the lead. When properly optimized the PSP is capable of near-PS2 graphics, which looking at the SGX's specs may be just a bit more than it can do. But we'll have to see what's done with it.

    The more limiting factor however is power consumption. The DS Lite is a champ here - on the lower screen brightness settings it gets over 10 hours running at full tilt. That's Nintendo's tradeoff on performance and power. The PSP isn't nearly as good, but even when everything is cranked up it can do about 4-5 hours (I'm going to ignore the UMD here), more if it's a 222mhz game.

    Both of these are well in excess of what the iPhone 3G got on its most demanding games. Even though the 3GS is faster, games aren't going to offer it much of an opportunity to drop to a lower power state since they're tasks that never end. For a 3G game I'd expect better battery life (50%, so 3 hours maybe?), but for a 3GS game it's likely going to be even worse.

    As you note the 3GS can eat more power, so if devs try to max it out (and they will, there's 20 years of console history that says shiny sells) it's reasonable to expect that it'll crash harder than even the 3G. Unless the SBX eats significantly less power, the worst case battery life scenario for the 3GS is going to be far worse than any dedicated handheld on the market, and worse than the existing 3G and iPod Touch.

    To that end, unless Apple can reign in on developers and make them NOT max out the hardware, I don't see handhelds going away any time soon. You'll get some convergence (e.g. solitaire) but the battery/hardware balance for a phone and a handheld are completely different. A gaming platform that only gets a couple of hours is a Sega Game Gear (or a Nomad, for the sadistic), and at least that had removable batteries.
  • psychobriggsy - Wednesday, June 10, 2009 - link

    Confirmation of 600MHz and 256MB RAM: http://www.t-mobile.nl/iphone/specificaties.html?W...">http://www.t-mobile.nl/iphone/specificaties.html?W...
  • sxr7171 - Wednesday, June 10, 2009 - link

    I GS must be faster than the N95's 3D acceleration as well, I know the 3G was slower, but this looks much faster. I've seen 3D demos on the N95 and wow they were impressive. At that 320x240 resolution it probably performed better than the PSP.
  • fyleow - Wednesday, June 10, 2009 - link

    The greatest weakness of the iPhone is the controls. Developers can get pretty innovative with the touch screen and accelerometer but really they can only do so much. id did a great job with Wolfenstein on the iPhone but the controls are still not as precise as physical buttons, and the controls take up the already limited screen estate of the phone.

    Nintendo threw as many input methods as possible with the mic, touch screen, physical buttons, and now camera. They also put in dual screens. The result is that developers could get wildly creative and I think it has been key to the DS' success because it allowed for some pretty innovative games.

    I've yet to see many "serious" games for the iPhone; most appear to be catered to very casual gaming. There's a huge market for that as evidenced by the Wii, but it's not ready to displace the dedicated hand held consoles yet.

    Yeah we'll probably see convergence happen down the road, but not in this or the next generation.

  • mesiah - Wednesday, June 10, 2009 - link

    The average phone user doesn't care much about games and game controls, so I don't really see apple or palm incorporating these into their phones and cluttering up the interface. But all it would take is for a company to create a peripheral that, say, the iphone snaps into and docks with that has an analog stick, some buttons, and some hand grips. Could even make it so it folds up when not in use. Something like that could really open up possibilities for gaming on iphone or pre. Just thinking about it makes me a little giddy hehe. Nintendo hand helds have always been too cheesy for me, but I can't bring myself to spend big money on a psp. Now if I can justify it with "but, its a phone and so much more." maybe my conscience would say "hey, your right! Go ahead and buy it."

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