Real-Time Operating Systems and Middleware

The Course:

The course web page changed: find the old (2011) page here

Slides:

Theory:

• Introduction to the course
• Real-Time Scheduling
• Real-Time Scheduling Analysis
  • Exercizes
• Shared Resources
• Scheduling with dynamic priorities
• Some notes on implementing scheduling algorithms. For fixed priorities, check kernel/sched/rt.c in the Linux kernel (functions pick_next_rt_entity(), __enqueue_rt_entity and __dequeue_rt_entity).
• Removing some restrictive assumptions
  • A reservation-based scheduling algorithm
  • MultiProcessor real-time scheduling
  • The Sporadic Server
• EDF scheduling in Linux
  • Something more on Real-Time Scheduling algorithms
• Summary about OS kernels
• The Timer Resolution Latency
• The Non-Preemptable Section Latency
• The Real-Time OS Kernels
  • Some slides about Linux Kernel Locking (enforcing consistency in a modern multithreaded kernel).
  • A paper about Real-Time on Linux

Practice (in the lab):

• Real-Time API - Part I
• Real-Time API - Managing the Concurrency
• The PThreads API
  • Introduction to PThreads
  • PThreads Synchronization
  • Example about pthreads and mutexes
• Compiling for embedded systems:
  • Scripts for generating an embedded FS
  • A version of busybox that compiles without issues on the computers in the lab
  • Package containing a kernel for the generated FS
  • How do the script work:
    • Some notes on CrossCompilers
    • How to build a filesystem for embedded devices
    • Filesystems for embedded devices: a summary
• Tutorial on writing real-time applications with POSIX
• Source code for an example RT application
• The Some slides about the Linux Kernel

NOTE: slides are periodically updated... Be sure to have the latest version!

For comments, qestions, etc. send me an email.

Captain's log:

• stardate 4515.5 (2014/09/15): Introduction to the course.
• stardate 4517.4 (2014/09/17): Introduction to Real-Time Programming (up to slide 12).
• stardate 4522.5 (2014/09/22): Real-Time Scheduling - Part I (up to slide 14).
• stardate 4524.4 (2014/09/24): Periodic timers, again (slides 13 to 21).
• stardate 4529.5 (2014/09/29): Real-Time Scheduling - Part II (from slide 14 to end).
• stardate 4531.4 (2014/10/01): Exercises and Examples on periodic timers (slides 21, 22 and 23). The exercise is about implementing a cyclic executive.
  • Code for the job bodies
  • Possible solution
• stardate 4536.5 (2014/10/06): Real-Time Scheduling Analysis.
• stardate 4538.4 (2014/10/08): More exercises on the cyclic executive
  • Fix some warnings by introducing a proper header file (remember: it must be included in cyclic.c!)
  • Modularize cyclic.c by introducing periodic_tasks.c and its header file periodic_tasks.h. The main file becomes much simpler: cyclic-1.c. (BTW, have a look at the coding rules).
  • Use a table to store the schedule: cyclic-table.c.
  start talking about Real-Time API - Managing the Concurrency (up to slide 9).
• stardate 4543.5 (2014/10/13): Exercises on schedulability analysis and introduction to Resource Sharing in real-time systems (up to slide 14).
• stardate 4545.4 (2014/10/15): Multiprocessing in POSIX - slides from 9 to 21 and related example programs:
  • fork.c. Compare it with thread.c
  • exec.c
• stardate 4550.5 (2014/10/20): Resource Sharing (slides from 15 to end)
• stardate 4552.4 (2014/10/22): Multiprocessing in POSIX, again - slides from 21 to end, with related examples:
  • oscillator.c: shows how to use signals to synchronise 2 user processes, and how to cope with zombies
  • rtsig.c
• stardate 4557.5 (2014/10/27): EDF
• stardate 4559.4 (2014/10/29): Implementing periodic tasks with processes.
  • Again, use the job bodies from cyclic_test.c
  • Again, re-use the periodic timers code (remember to include the proper header file)
  • Here is a incomplete solution not setting real-time priorities
  • Here is a more complete solution that sets correct real-time priorities
  Introduction to pthreads (up to slide 7)
• stardate 4564.5 (2014/11/3): Implementing real-time schedulers, and real-time in the real world
• stardate 4566.4 (2014/11/5): pthreads and related exercises - from slide 7 to the end
  • Create a thread
  • Compare thread.c and fork.c
  • Implement 3 periodic tasks using threads... As usual, use cyclic_example.c for the job bodied
  • Possible incomplete solution that does not set the thread priorities
  • More complete solution that sets correct thread priorities
• stardate 4571.5 (2014/11/10): Multiprocessor real-time scheduling and EDF on Linux.
• stardate 4573.4 (2014/11/12): Pthreads again and pthreads synchronisation
  • pthreads slides, to the end
  • Example on mutexes
• stardate 4578.5 (2014/11/17): Real-Time OSs: executing real-time tasks in the real world.
• stardate 4580.4 (2014/11/19): Some notes on CrossCompilers.
• stardate 4585.5 (2014/11/24): The Timer Resolution Latency.
• stardate 4587.4 (2014/11/26): Building a filesystem for embedded devices.
• stardate 4592.5 (2014/12/01): The Non-Preemptable Setion Latency and how to reduce it (up to page 6).
• stardate 4594.4 (2014/12/03): Embedded filesystems, again. Based on the embedded filesystem built in previous lessons:
  • Install real-time applications on the filesystem
  • Automatically start the real-time applications at boot
  • Reduce the filesystem image size
• stardate 4604.5 (2014/12/15): Techniques for Real-Time kernels.

References:

• A good Operating System book (I suggest ``Operating Systems'' by William Stallings, but ``Operating Systems Design and Implementation'' by Andrew Tanenbaum, or similar books are OK too). As an example here is a list of the interesting chapters in ``Operating systems. Internals and design principles; 7th ed.'' by W. Stallings.
• For the Real-Time Scheduling part, interested students can consult ``HARD REAL-TIME COMPUTING SYSTEMS: Predictable Scheduling Algorithms and Applications'' by Giorgio Buttazzo (Springer, 2005) - There is an italian version of the book, too.
• For the Real-Time programming part, consult the Open Group site (in particular, have a look at the real-time extensions)
• Another good reference for people interested in Unix programming is ``Advanced Programming in the Unix Environment'' by W. Richard Stevens (Addison Wesley)

Funny Stories:

• About the Mars Pathfinder

Projects:

A preliminary list of possible projects for the exam is available. Email me if you have questions

Other Material:

• Some notes about C Coding
• Some notes about writing Makefiles
• For experiments on operating system kernels, the qemu emulator will be used. If you are impatient and you want to start playing with the emulator now, here you can find version 1.7 precompiled and ready to be used on a Linux system. Just download the tarball and uncompress it in /tmp. Have a look at the qemu site for instructions about how to use it.
• A cross-compiler for ARM
• A patched version of busybox that works on the computers in A104
• The package containing the ARM test kernel
• Some scripts for generating an initramfs
• The kernel headers for compiling test Linux modules (for ARM)
• How to use xenomai
• Example about Linux Kernel Modules, and some instructions for compiling and using kernel modules.

Some Practice at the Computer...

If you want to see how the theory studied in the course applies in simple programming exercizes, check this link.

The Exam

Are you ready?

The texts of some of the previous exams:

• January 18 2011
• February 15 2011
• June 7 2011
• July 19 2012
• September 14 2012
• January 15 2014

Remember to send me your projects some days in advance respect to the exam, so that I can evaluate them.