Socorro NM — (press release excerpt) — FSMLabs has announced a kernel patch which will make RTLinux (and other real-time Linux variants) work reliably on the recent Linux 2.4 kernels. According to Michael Barabanov, FSMLabs principal systems engineer, a little-noticed change in Linux low-level memory management can produce increased timing uncertainties and unpredictable system errors in any Linux-based… software that relies on the kernel mode memory properties found in previous versions of Linux. The change was intended to optimize average case performance of Linux in mainstream Linux applications, but introduces the possibility of memory faults into the operation of even the lowest level software.

“For realtime developers using the newest and latest Linux editions, this change has caused mysterious and confusing failures,” said Barabanov. Thanks to an active and technically savvy user communty, the bug was uncovered rapidly. While fixing the problem for RTLinux customers was the top priority, FSMLabs decided to make a general release of the patch available. The patch for Linux 2.4.2 is available for free download, here.

Barabanov noted that this problem illustrates the complex interaction between the need to optimize Linux for desktop and server tasks and the sometimes conflicting requirements of real-time and embedded Linux users. Because Linux is open source, and because the design of RTLinux separates real-time software from the Linux kernel itself, robust engineering solutions to these problems can be found, and the advantages of using the Linux kernel far outweigh the costs of tracking kernel development.

RTLinux is a low-overhead hard real-time operating system which provides a flexible standards-based threading environment. RTLinux runs the Linux OS as a task that is never permitted to delay or interfere with the actions of timing-critical software. RTLinux worst-case interrupt latency is hardware dependent — no more than 20 microseconds on standard PC hardware and no more than 5 microseconds on some embedded boards. RTLinux provides full access to the Linux development environment and applications. This encourages a robust style of software design with a rapid, low cost development cycle, one which makes use of the enormous range of existing software available under Linux.

 
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