FSMLabs and Infineon Technologies claim to have achieved the world's first demonstration of a Linux mobile phone based on a single processor core: a working prototype based on a single ARM9 core running FSMLabs's RTLinux real-time Linux OS, along with a functional 2G/3G (WCDMA/EDGE/GPRS/GSM) stack from Infineon's wholly-owned subsidiary, Comneon.

FSMLabs CEO Victor Yodaiken notes, “It's nice to be able to talk about this now. We did all the engineering last year, and have had working systems for a while now.”

He adds, “FSMLabs has built its business on replacing dedicated hardware with microprocessors, and I predicted this would happen about seven years ago. Once you have a high-speed applications microprocessor in there, you can use it to replace other things. The idea is not limited just to handsets.”

Single-what mobile phones?

Current-generation mobile phones based on “complex OSes” such as Symbian, Linux, and Windows use two separate processors to run all of their embedded software. An applications processor runs the high-end OS, GUI, and user applications, while a “baseband” processor runs a low-level RTOS (real-time OS) that handles signal-plane functions such as managing the cellular radio and its communications protocols.

Because the use of two processing subsystems increases BOM (bill of materials) costs, space requirements, and power consumption, numerous parallel efforts appear to be underway to create single-core or single-chipset mobile phone designs that can bring the advantages of complex OSes to the high-volume, mid- to low-priced feature-phone market, which promises to dominate the cellphone market by 2010.

Specifically, over the past year, efforts to work towards single-core or single-chipset designs have been announced by a variety of embedded Linux and virtualization software vendors, including MontaVista, Jaluna, Mizi Research, Trango, and NICTA, an Australian think-tank whose virtualization technology was adopted commercially by Qualcomm, it says. Meanwhile, SoCs targeting single-chipset phone designs have been announced by Renesas, Qualcomm, Texas Instruments, and others.

FSMLabs notes that, in addition to the obvious benefits of lower material costs and reduced power consumption, single-chip/chipset designs also eliminate performance bottlenecks imposed by legacy serial line communication with the modem processor. Yodaiken explains, “Instead of two PCs networked by a slow serial line, you have everything in a central place. The control plane now actually has visibility into performance, what networks are available, and how congested they are, and there are obvious things it can do, such as adjusting compression or using WiFi instead of GSM, when it's available.”

The Infineon/FSMLabs demo

RTLinux comprises a tiny, hard-real-time kernel called “RTCore,” which has its own POSIX API and runs Linux as an idle task. The FSMLabs/Infineon demonstration involves Comneon's GSM/GPRS/EDGE stack running in the RTCore real-time domain, along with drivers for Infineon's 2.5G and 2.75G radios. Meanwhile, a Linux kernel, smart phone utilities, and graphical user interfaces run concurrently in the non-real-time domain.

According to Yodaiken, a requirement for Infineon was that the cellular networking stack run unmodified, which led to some work on FSMLabs's behalf. He said, “There was work on RTCore required to get the scheduling to operate properly, and to host the GSM/GPRS/EDGE stack. It was a threaded stack originally written for Nucleus.”

In order to support the Nucleus stack, FSMLabs ended up writing a Nucleus application binary interface, an accomplishment Yodaiken downplays. “Nucleus is mainly about threads. If you have threads already, you're 90 percent of the way there,” he explained.

Yodaiken says RTLinux-powered 2.5G and 3G mobile phones “may be in production soon, given market trends suggesting that fast real-time capability is one of the key barriers to a broad implementation of Linux in mobile devices.”

Hard real-time performance also suits media-rich mobile-phone communications “where task-level response requirements for 3G media rich applications such as video streaming and video telephony are in the tens to hundreds of microsecond ranges,” he adds.

Yodaiken emphasizes that his company's commercial RTLinux product offers a “common, vendor-neutral real-time approach” to enabling Linux to run in both control and signal planes. RTLinux supports normal Linux distributions and device drivers, and, unlike many Linux phone implementations available today, can run normal Linux applications, he says.

Another potential advantage is that the telephony stack runs under RTCore, rather than Linux, thereby avoiding potential GPL concerns.

Infineon does not have an exclusive license, Yodaiken confirms. He says he hopes other mobile phone chip companies will consider RTLinux for single-core mobilephone chipsets. He adds, “Infineon were the guys who saw the technical possibilities, and put the effort into [single-core Linux phones] well before everyone else. They did a thorough job of evaluating all available technologies, and they chose us. This is a great validation of our real-time Linux technology.”

 
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