RT-Linux: Ross Johnston Jonathan Blackburn Jason Siciliano

Introduction RT-Linux: Past and Present What is real-time, and how does RT-Linux handle it? How is RT-Linux different from other real-time systems? Scheduling Algorithms (FIFO)

The Basics of RT-Linux Victor Yodaiken and Michael Barabanov created RT-Linux at the Institute for Mining and Technology of New Mexico in 1997 RT-Linux is maintained by FSMLabs, Inc. Allows the Linux kernel to run off of the RT-Linux kernel, sharing the processor

What is a “Real-Time” System? “Real-Time” constitutes process scheduling meant to meet a deadline; little to no event latency allowed There are “hard” real-time systems (failure to meet deadlines results in serious consequences) and “soft” real-time systems (failure only results in quality degradation)

RT-Linux handling Real-Time Interrupts are handled based on RT-Linux options – either by enabling or disabling interrupts –When enabled, the main Linux kernel handles interrupts normally –When disabled, pending interrupts are held until interrupts are re-enabled This is known as Interrupt Emulation

RT-Linux: How is it different? RT-Linux functions basically with a “dual kernel”; it builds a small kernel over the processor, complete with its own scheduler –The Linux Kernel still functions, handling all non- RTLinux processes Most other real-time systems, instead, modify the kernel in order to guarantee predictability

RT-Linux & FIFO RT-Linux uses First In First Out (FIFO) queues for inter-process communication FIFO queues are similar in design to pipes in Unix RT-Linux processes view the FIFOs as simply integers, while Linux processes see them as character devices

Scheduling in RT-Linux Users can implement their own schedulers using loadable kernel modules Comes with two schedulers – Priority-based Preemptive & Earliest Deadline First