Anand's Google Nexus One Review

Inside Snapdragon is a Scorpion

Several years ago Qualcomm assembled an architecture team in the Research Triangle Park in NC, coincidentally around 30 minutes from where I live. One of their tasks was to design a high performance CPU core around the ARMv7 instruction set. They called it Scorpion.

While the Scorpion core is normally referred to as a Cortex A8, Qualcomm views it as more of a Cortex A9 competitor. The truth, as always, lies somewhere in between. Like the Cortex A8, Scorpion is a dual-issue in-order microprocessor architecture. As I mentioned in my iPhone 3GS article, you can think of it as a modern day Pentium processor (but not an Atom).

Qualcomm claims the ability to do some things out of order, but by and large the pipeline is in order which ultimately keeps it out of the A9 classification.

Qualcomm hasn't shared much about the base architecture other than to say that it's definitely not based on the Cortex A8. It might have a deeper pipeline than the Cortex A8 to help it reach higher clock speeds. Unlike the ~600MHz target the A8 will hit at 65nm, Qualcomm's Scorpion will run at 1GHz at 65nm.

Scorpion also implements the NEON extensions to the ARMv7 ISA, although Qualcomm's implementation is a higher throughput version of what the Cortex A8 offers. It's my understanding that NEON isn't very widespread in usage today, so I'm not sure that Qualcomm's advantage here matters just yet.

Cache sizes are unknown but I'd expect that they're competitive with what we've seen from competing Cortex A8 implementations. Ultimately everyone is bound by die size and power consumption at 65nm.

Qualcomm integrates the Scorpion core in its Snapdragon SoC. The version of Snapdragon in the Nexus One is the QSD8250. This SoC includes a 1GHz Scorpion core and an integrated 3G modem. The QSD8650 will be used in the Verizon version with support for EVDO and CDMA 2000.

Qualcomm's integrated modem is a very different approach from what we've seen from companies like NVIDIA, Apple/Samsung and TI. Those companies rely on an external modem solution to reduce time to market. Qualcomm's response is to instead offer an SoC that integrates support for all major wireless standards. The QSD8250 used in AT&T's supports GSM, GPRS, EDGE and HPSA networks.  The QSD8650 supports CDMA2000 1X, 1xEV-DO Rel 0/A/B, GSM, GPRS, EDGE and HSPA wireless networks.

When I spoke with Qualcomm one message it stressed was how calculated the timing of Snapdragon was. It's not by accident that all of the major Android phones being announced today use Snapdragon, it's because of very careful timing and planning that Qualcom was able to hit this bulge in the market. Most SoC makers would cite time to market as a reason for not integrating a modem into an application processor, it's clear that Qualcomm faced that challenge and took timing very seriously with Snap Dragon.

The CPU side of the Snapdragon SoC is fast. Faster than what's in the iPhone 3GS, Palm Pre and Motrola Droid. Unfortunately there are other issues. Qualcomm scaled up processing speed but didn't increase memory bandwidth. The Snapdragon still has a 32-bit LPDDR1 interface, giving it the same memory bandwidth as its competitors despite boasting a much higher clock speed.

The even bigger problem with Snapdragon is its use of the Adreno 200, a dated and slow GPU Qualcomm acquired from ATI a couple of years ago. Luckily for Qualcomm, intensive 3D gaming hasn't really taken off on smartphones just yet but here Snapdragon is at a disadvantage to the Samsung and TI SoCs that use Imagination Tech's PowerVR SGX.

So the Nexus One has better CPU performance, identical memory bandwidth and worse GPU performance compared to the iPhone 3GS. Nothing is ever easy in this world.

Later this year Qualcomm will introduce its 45nm Snapdragon SoCs. These will range from being simple clock bumps of the 8650 in the Nexus One with LPDDR2 support, to full fledged dual-core versions with a much higher performance 3D core. Qualcomm also confirmed its intentions to move to an out-of-order architecture at some point in the future. I'd expect to hear more about that next year.