SAN MATEO, Calif. — As Linux has become trendy, so has the idea of adapting it to real-time environments. But Linux isn't inherently suited for real-time work, and that's led at least one company to pursue a different path to real-time.
Dubbed RTLinux, the OS doesn't try to change Linux into an RTOS, but instead provides a homemade RTOS kernel that incorporates Linux as a low-priority thread. Thus the RTOS stays as small and streamlined as possible — a principal goal of RTLinux's creators — while retaining Linux as the basis for common applications.
"We have a very clear model that we're trying to educate people on," said Victor Yodaiken, who led the development of RTLinux.
June 15 marked the pre-beta release of RTLinux version 3.0, which is compatible with the still-in-progress 2.4 version of the Linux kernel as well as the current 2.2 version. In addition to writing for the X86 platform, the RTLinux crew finished a PowerPC port in November, and more recently completed a port for the Alpha microprocessor.
Yodaiken's original work on RTLinux "was aimed at trying to solve what we saw — and I still see — as the biggest problem in real-time system design," he said. "Real-time systems are very simple and handmade. They were developed around very simple operating systems that didn't do much. Now, people want a real-time controller in every toaster, to present a Web interface or a GUI, and the question is, how do you [provide] that as a standard real-time operating system that works?"
To address that issue, Yodaiken and his students at the computer science department of the New Mexico Institute of Mining and Technology developed RTLinux with the goal of keeping the real-time kernel small and nimble. That way, the kernel delivers hard real-time performance to the functions that need it, while complicated, non-real-time functions such as a graphical user interface are passed on to Linux.
In addition, RTLinux is flexible with which Linux distribution it uses — any standard distribution will do.
Since January, Yodaiken has been on leave from the New Mexico Institute to work full-time on RTLinux, which started as a research project in the mid-'90s. As chief executive of Finite State Machine Labs Inc. (Soccoro, N.M.), he's been on the lecture circuit, giving talks at the bevy of Linux conferences that have sprouted during the past year.
In building FSM Labs' team, Yodaiken has taken advantage of e-mail and Web-based operations to build what he called a "mini-multinational," with a handful of staffers scattered in locations such as Russia, Vienna and Los Angeles.
With RTLinux on an X86 platform, interrupt handlers can spring into action within 15 microseconds of the detection of a hardware interrupt, compared with 600 microseconds for standard Linux. That time window is actually determined by hardware and will improve as processors get faster, Yodaiken said.
In addition to providing real-time performance, RTLinux's split nature saves time in application development, because familiar Linux software can be used for functions such as Web browsing.
"The key piece is, we don't require much of a modification to Linux," Yodaiken said. "We really believe we're going to profit from all the work going into embedded Linuxes, because all those embedded Linuxes can fit into our system."
For an application programming interface (API), FSM Labs chose late last year to stick to the Posix 1003.13 standard, which contains profiles for "hard" real-time systems, such as the RTLinux real-time core, as well as for multipurpose systems such as Linux.
FSM Labs focused on the Posix APIs before individual companies began touting their own APIs as a way to unify widespread embedded Linux efforts. FSM Labs has shunned those efforts in favor of sticking with pure Posix compliance, something Yodaiken says customers find comforting.
"Our belief is that that gives us a good combination," he said. "We have a standards-based API, access to Linux, and real-time performance."
As with many embedded-system projects, RTLinux has found its way into a range of novel applications, including NASA's "vomit comet" planes used to simulate freefalls, the manufacturing of chainsaw chains, and Muppet-controlling computer systems for The Jim Henson Co. (Hollywood, Calif.).
Key applications so far have been centered on instrumentation and industrial control. But also looming is the prospect of the telecom and datacom markets, areas FSM Labs is beginning to tackle.
"I don't think people have appreciated how fast Gigabit Ethernet is," Yodaiken said. "If you're trying to do something with low latency with Gigabit Ethernet, you have interrupts of less than two microseconds. We're going to be able to handle that."
