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Real-time Linux kernel available for ARM9 CPUs

Jun 6, 2008 — by Eric Brown — from the LinuxDevices Archive — 11 views

Embedded Linux developer services provider Timesys is distributing a real-time Linux kernel for ARM9-based Atmel processors. The kernel includes Ingo Molnar and Thomas Gleixner's RT_PREEMPT patch, along with patches for high-resolution timers and other board-specific features for Atmel reference platforms.

The “RT Preempt” patch is the same used by Linux distributors Red Hat, Novell, and MontaVista, in the real-time versions of their commercial real-time Linux distributions. It is expected to reach the mainline kernel eventually, but has not been generally available pre-integrated into a full kernel offering. The patch provides guarantees for hard timing deadlines, required by many mission critical applications in industries like telecom, military, healthcare, or financial trading.

The new kernel and patches have been applied, configured, and tested to support real time features, says Timesys, although it did not say by whom. The kernel supports full kernel preemption, schedule-able interrupt handlers, high resolution timers, and mutexes with priority inheritance, says the company. The optimized kernel supports the Atmel ARM9-based reference platforms, including the AT91SAM9260, AT91SAM9261, AT91SAM9263, AT91SAM9RL, AT91CAP9, and the new 400MHz version with 32KB instruction and data caches, the AT91SAM9G20.

A TimeSys spokesperson listed features and capabilities of the optimized kernel and patches as follows:

  • Better POSIX compliancy — supporting real-time implementation of POSIX interfaces including signals and message queues
  • Fully preemptible Big Kernel Lock (BKL) — enabling low priority tasks to hold Big Kernel Lock without increasing latency
  • Full real-time preemption — reducing kernel latencies by minimizing non-preemptible kernel sections
  • Threaded Interrupt Service Routines (ISR) — improving response time for real-time tasks under heavy interrupt load
  • High-resolution timers — reducing delays for activities that must be triggered by timeouts that are “less than one jiffy”
  • Mutex priority inheritance support — eliminating unbounded priority inversion for system and user tasks on kernel and user-space mutexes
  • Debugging and tracing — enabling tracing of Linux kernel latencies during execution
  • Full configurability — user-controllable tradeoffs between kernel latency and throughput

The Atmel real-time kernel LinuxLink subscription includes a Linux reference distribution, integrated and tested for select Atmel reference platforms. The subscription is said to provide the toolchain, hundreds of pre-built binary package built with both glibc and uClibc, web-based support and documentation, and optional TimeStorm development tools.

Stated Greg Quiggle, VP of Sales and Marketing for Timesys, “The community has made great strides with respect to real time Linux performance.”


The Atmel real-time kernel LinuxLink subscription is available now, says Timesys. More information may be found here.

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