Microprocessor Architecture Wars Come to Roost in the Embedded Market: Intel versus ARM

Microprocessor vendors have been waging war to win processor sockets since there were at least two microprocessors to compete. In the 1980s, it was RISC (reduced instruction set computers) versus CISC (complex instruction set computers), and RISC won. Today, nearly all processors are RISC on the inside whether or not they are based on an instruction set originally associated with a RISC or CISC architecture. During the 1990s, as PC shipments climbed to 100 million per year, the war switched from RISC verses CISC to Intel verses AMD. The “best” x86-processor title ping-ponged back and forth between the companies from one generation to the next as clock rates climbed to almost 4GHz until Intel decided to stop playing around and simply go after the competition with processors of mass destruction. In the 2000s, we have had the multi-core wars based on how many processor cores the processor vendors can get to dance on the head of a chip. Now, as we head into the 2010s, we have a new war erupting, and this time, it’s on the embedded front. Instead of Intel verses AMD, it’s Intel verses ARM.

ARM set the stage for this war nearly 10 years ago when it rolled out the ARM Thumb instruction set. Thumb instructions are a 16-bit subset of the original ARM 32-bit instructions. While Thumb instructions are a little less able than their 32-bit cousins are, Thumb-2 instructions are half as large, making them much better suited to the limited memory provisioning in many embedded systems designs. With the Thumb instruction set and subsequent and improved Thumb-2 instruction set, ARM clearly indicated its intention to invade the embedded space. And, ARM has been remarkably successful. ARM processor cores have been appearing in a wide variety of microcontrollers from a long list microcontroller vendors, including Analog Devices, Atmel, Cirrus, Energy Micro, Freescale, Nuvoton (formerly the logic IC business of Winbond), NXP, Sharp, STMicroelectronics, Texas Instruments, Toshiba, and Zilog.

The embedded niche seemed to be a safe bet for ARM – a haven from the Intel processor juggernaut in PC space. Intel’s Pentium and subsequent processors were scaling the GHz wall and needed tens of watts of electrical power, big heat sinks, and forced air or water-cooling. These high-powered processors sought PC sockets and were simply not suitable for most embedded designs. They embedded space seemed calm by comparison, although it was too populated by many hungry 8-, 16-, and 32-bit processor vendors.

Then, the “netbook” happened. Netbooks are lightweight, diminutive laptops with correspondingly small batteries and not much power to run a top-of-the-line PC processor. Their small size also made it difficult to ditch the waste heat of these high-powered processors. They needed a processor with good performance that sipped power. Intel coveted those sockets, and the Intel Atom processor was born.

Intel’s Atom processor took an entirely different approach to processor design. The Atom architecture team took a clean sheet approach to the design. They judged every feature and option from a performance/power perspective. The Atom design team only added the most power-efficient features. Everything else was eliminated. The Intel Atom design team also took a giant step backwards in time and discarded the deconstruction of x86 instructions into micro-ops, which has RISC-ified the Pentium architecture. Instead, the optimized the Atom processor’s pipeline to directly execute x86 instructions. The design team also added SMT (simultaneous multithreading), because it delivers a performance/power payback ration of 2x, which fits the selection criteria discussed above.

As a result, Intel’s Atom has a TDP (thermal design power) rating of 2W, and Intel has already introduced two Atom processor generations with multiple processors in each generation. Certainly, 2W is not the lowest power dissipation you can find in an embedded controller (and the Atom companion US15W chipset more than doubles that number). However, it is well within the power constraints of many embedded systems designs, and the Atom’s immense software compatibility with nearly any PC program and software development tool makes it a very attracted embedded processor architecture. Accordingly, a big portion of the embedded market is suddenly in a battle zone coveted by both ARM and Intel. The battle lines were not drawn. The initial skirmishes have commenced. The newest processor war is at hand, and embedded systems developers will benefit from the competition.