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http://www.mech.kuleuven.ac.be/~bruyninc/rthowto/ ----------------------------------------------------------------------------- Real Time and Embedded HOWTO Herman Bruyninckx, K.U.Leuven, Belgium Abstract This HOWTO is about the fundamentals of (i) real-time and embedded operating systems (focusing mostly on their differences with general purpose operating systems such as Linux), and (ii) real-time programming. Everything is illustrated with Open Source examples: RTLinux, RTAI, eCos, RT-EMS, uCLinux, ... (The discussion is somewhat biased towards the Linux derivatives.) This text also talks about design issues and Software Patterns for real-time applications. Table of Contents About this HOWTO....................................................................................................... i 1. Purpose/Scope of this HOWTO........................................................................... i 2. Feedback ............................................................................................................. ii 3. Copyrights, Licenses and Trademarks ................................................................ ii 4. Acknowledgments.............................................................................................. iii Part 1. Basics .................................................................................................................. i 1. Real-time and embedded operating systems........................................................1 1.1. OS responsibilities ....................................................................................1 1.1.1. Interrupt servicing..........................................................................1 1.1.2. Communication and synchronization ............................................2 1.1.3. Memory management ....................................................................2 1.1.4. Task management...........................................................................2 1.2. Trade-offs..................................................................................................3 1.3. Time ..........................................................................................................5 1.3.1. Real time ........................................................................................5 1.3.2. Latency...........................................................................................7 1.3.3. Timing constraints..........................................................................7 1.3.4. Data structures ...............................................................................8 1.4. Linux for real-time and embedded............................................................9 1.5. Operating system standards ....................................................................17 2. Task management and scheduling .......................................................................1 2.1. POSIX thread management.......................................................................2 2.2. Scheduling.................................................................................................3 2.3. Priority-based scheduling..........................................................................5 2.4. The Linux scheduler .................................................................................7 2.5. Real-time scheduling for Linux ................................................................8 3. Interrupts ............................................................................................................12 3.1. Introduction.............................................................................................12 3.2. Bottom halves (DSR) and top halves (ISR) ............................................15 4. IPC: synchronization and data exchange ...........................................................17 4.1. Introduction.............................................................................................17 4.2. Synchronization: events and locks..........................................................20 4.2.1. Race conditions............................................................................20 4.2.2. Events...........................................................................................24 4.2.3. Atomic operations........................................................................26 4.2.4. Locks............................................................................................27 4.2.4.1. Lock types.........................................................................30 4.2.4.2. The condition variable/mutex pattern for resource access33 4.2.4.3. Priority inversion...............................................................34 4.2.4.4. Priority inheritance and priority ceiling............................36 4.2.5. Lock-free synchronization ...........................................................37 4.3. Data exchange.........................................................................................39 4.3.1. Shared memory ............................................................................40 4.3.2. FIFOs ...........................................................................................41 4.3.3. Circular buffers ............................................................................41 4.3.4. Swinging buffers ..........................................................................42 4.3.5. Messages and mailboxes..............................................................43 4.3.6. Remote Procedure Calls...............................................................44 5. Memory management ........................................................................................45 5.1. Introduction.............................................................................................45 5.2. Shared memory in Linux ........................................................................47 5.2.1. Allocation at boot time.................................................................48 5.2.2. Allocation in kernel space............................................................50 5.2.3. Allocation in module....................................................................50 6. Real-time device drivers ....................................................................................51 6.1. Introduction.............................................................................................51 6.2. Comedi....................................................................................................52 6.3. Real-time serial line ................................................................................53 6.4. Real-time networking..............................................................................53 7. Linux variants for real-time and embedded .......................................................54 7.1. Real-Time Linux.....................................................................................54 7.1.1. The RTLinux patent .....................................................................55 7.2. RTAI........................................................................................................56 7.3. miniRTL..................................................................................................57 7.4. AtomicRTAI............................................................................................57 7.5. uCLinux ..................................................................................................57 7.6. Etlinux.....................................................................................................57 8. Non-Linux RTOSs .............................................................................................59 8.1. eCos.........................................................................................................59 8.2. RT-EMS ..................................................................................................59 8.3. CubeOS...................................................................................................59 8.4. FIASCO and DROPS..............................................................................59 8.5. Real-time micro-kernel ...........................................................................60 8.6. KISS Realtime Kernel.............................................................................60 9. Cross compilation & (remote) tracing and debugging.......................................61 Part 2. Design ...............................................................................................................62 10. Decoupling structure and functionality............................................................63 10.1. Components ..........................................................................................64 10.2. Architecture...........................................................................................66 10.3. Coupling................................................................................................66 11. Software Patterns .............................................................................................68 11.1. Component distribution and communication........................................68 11.2. Motion control ......................................................................................68 11.3. Device driver.........................................................................................69 11.4. Transaction and Rollback......................................................................69 12. Framework .......................................................................................................70 13. Hints.................................................................................................................71 13.1. Locks.....................................................................................................71 13.2. Patterns..................................................................................................73 Bibliography .................................................................................................................74 -------------------------------------------------------------------------------- armix -------------------------------------------------------------------------------- fabulous. long live,master. here's a link published much of in korean,but most of it is written in english. www.kernelkorea.org ---------- certainly, a site OS kernel relevant. -------------------------------- hode your hopes, devote your tries, everyday, a little step forward.