Super Simple Tasker

Super Simple Tasker Miro Samek and Robert Ward This README file describes the code accompanying the ESD article “Super Simple Tasker”. The SST code is fully portable ANSI-C. However, the SST example described in the article has been designed for a Windows PC. Installation ------------ The code is provides in a ZIP file, which you can decompress into a directory of your choice. Henceforth, this directory will be referred to as <sst>. Licensing ------------ The SST source code and examples are released under the terms of the GNU General Public License version 2 (GPL) as published by the Free Software Foundation and appearing in the file GPL.TXT included in the packaging of this file. Please note that GPL Section 2[b] requires that all works based on this software must also be made publicly available under the terms of the GPL ("Copyleft"). Files and Directories --------------------- After decompression, the <sst> directory contains the following subdirectories and files: <sst>\ | +-readme.txt - this file | +-gpl.txt - the GNU General Public License | +-example\ - subdirectory containing the SST example files | | | +-bin\ - contains .OBJ, .EXE, and .MAP files | +-bsp.c - Board Support Package for DOS/Turbo C++ 1.01 | +-bsp.h - BSP header file | +-kbd_task.c - The keyboard task function | +-main.c - The main function | +-sst_exa.h - The header file for the SST example application | +-sst_exa.prj - The Turbo C++ project file for building and | | debugging the SST example application from the | | Turbo C++ IDE | +-sst_port.h - SST port to DOS/Turbo C++ 1.01 | +-stdint.h - The C99 standard exact-width integer types | | for the Turbo C++ 1.01, which is a pre-standard | | compiler. You could copy this file to the | | Turbo C++ include directory. | +-tick_tsk.c - The two tick tasks (tickTaskA and tickTaskB) | +-include\ - subdirectory containing the SST public interface | +-sst.h - The platform-independent SST header file | +-source\ - subdirectory containing the SST implementation +-sst.c - platform-independent SST implementation Running the SST Example ----------------------- The executable file for the SST example is provided in <sst>\example\bin\sst_exa.exe. You can run this executable on any Windows-based PC in a DOS-console by simply double-clicking on the executable. However, the program takes one command-line argument, which is easiest to provide by launching the program from a command prompt. The command-line argument determines the number of iterations through a delay loop peppered throughout the application code. The purpose of this delay is to extend the run-to-completion processing (which is really short on the fast modern PCs), and thus increase the probability of asynchronous preemptions. We’ve been using a typical value of this delay around 10000 on a modern 2GHz PC, which corresponds to the following invocation of the SST example application: sst_exa.exe 10000 As described in the article, you should not go overboard with this parameter because you can eventually overload the machine, and the SST will start losing events (the queues will overflow and won’t accept new events). Once the application starts running, you can generate asynchronous preemptions by typing on the keyboard. The keyboard interrupt is asynchronous with respect to the periodic time-tick interrupt and consequently the keyboard interrupt can preempt the time tick tasks (that run just after the tick interrupt), and the time tick interrupt can preempt the keyboard task (that runs just after the keyboard interrupt). Moreover, the interrupts can also preempt each other. Please note, however, that the tick ISR has the highest priority, and consequently the Programmable Interrupt Controller (the 8259A chip) will not allow in hardware that the lower-priority keyboard ISR preempts the highest-priority tick ISR. The only allowed interrupt preemption is that tick ISR preempts the keyboard ISR. You should verify this by observing the “Preemptions” column of the application display. After typing for a while on the keyboard, you should see some cases of the asynchronous preemption in the “Preemptions” column. The synchronous preemptions are not displayed, but they occur every time a keyboard task posts an event to the higher-priority tickTaskB(). On the other hand, the synchronous preemption does not occur when the keyboard task posts an event to the lower-priority tickTaskA(). Borland Turbo C++ 1.01 ---------------------- In order to modify and recompile the example, you need to download and install the legacy Turbo C++ 1.01 compiler, which is available for a free download from the Borland Museum at http://bdn.borland.com/article/0,1410,21751,00.html. The legacy DOS platform has been chosen for demonstrating SST because it still allows programming with interrupts, directly manipulating CPU registers, and directly accessing I/O space of the processor (required for writing the EOI command to the 8259A interrupt controller). No other desktop 32-bit development environment for the commodity PC allows this much so easily. The ubiquitous PC running under DOS (or a DOS console within any variant of Windows) is capable of demonstrating most key embedded features of SST. To install Borland Turbo C++ 1.01, download the file TCPP101.ZIP from the Borland Museum and unzip it into a temporary directory. Run the INSTALL.EXE program and follow the installation instructions. Integrating SST with State Machines ----------------------------------- As described in the article, SST-type kernel is ideal for deterministic Run-To-Completion (RTC) execution of concurrent state machines. The website www.quantum-leaps.com provides an implementation of the RTC kernel, called Quantum Kernel (QK) that works exactly like SST and only differs in the way it is integrated with the state-machine event processor (QEP) and the state machine framework (QF). All these components are available under the GPL open source license. Miro Samek Email: miro@quantum-leaps.com Internet: www.quantum-leaps.com April 24, 2006