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