doc-intro.h

ucos2.8 移植到linux下的代码

/**
 *  \mainpage Introduction
 *  \author George Fankhauser
 *
 * This documentation describes the port of microC/OS-II to the Linux user
 * space target. As with real hardware, the porting abstraction layer has
 * been implemented using system and library calls.
 *
 * The basic functionality has been implemented to provide all microC/OS-II
 * services. As the RTOS (Real-Time Operating System) does not provide any
 * I/O abstractions (driver models etc.) additional funtionality and hardware
 * interfacing has to be provided by the programmer.
 *
 * For demonstration purposes, output functions for a terminal are implemented.
 * In addition, some of the timing functions found in the DOS/PC examples 
 * have been implemented on Linux to run the demos properly.
 *
 * The following screen shots show these examples. Program #1 has been changed 
 * in its appearance. Program #2 has an additional function that fills up one
 * tasks stack over time.
 *
 * \image latex "../doc/ex1.png" "Example #1 from the book running 7 Threads (colorised version)." width=0.75\columnwidth
 *
 * \image latex "../doc/book2.png" "Example #2 from the book. This example shows the stack checking feature and measures time for the checking. The example has been modified with a recursive function that fills the stack using random numbers as a parameter. Note Task 4 which runs dangerously low on stack memory." width=0.75\columnwidth
 *
 * \image latex "../doc/book3.png" "Example #3 from the book timing some tasks while exchanging messages." width=0.75\columnwidth
  *
 * \section details Linux Interaction
 *
 * The basic port has been mapped onto Linux signals and is implemented in
 * os_cpu_c.c; note that there is no assembly file in this port. Some of the 
 * functionality is inlined in os_cpu.h. In other words, there is only one
 * Linux process (also only one thread) and all the task creation and scheduling
 * is done by microC/OS-II. 
 *
 * Signals are delivered on the current tasks stack. OSTCBStkPtr is made
 * pointing to the ucontext_t structure on the stack for later use.
 *
 * - OS_TASK_SW(): The context switching on system calls is implemented using 
 *   the Linux kill() syscall which sends the signal SIGUSR1 to itself.
 * - OSCtxSw(): Switching tasks is done after an interrupt has occured and a 
 *   new task becomes ready to run, or, a task voluntarily gives up the CPU.
 *   This function is called by the signal handlers for SIGUSR1 and SIGALRM.
 *   Switching is done by setcontext().
 * - OSTickISR() is a standard implementation as described in the book. It
 *   is periodically called by the OSTimeTickSigHandler().
 * - OSInitHookBegin(): This hook is used to initialise Linux signals and
 *   handlers. It calls linuxInit()
 * - linuxInitInt() has to be called by the user in the first task. It starts
 *   the clock ticking.
 * - OSTaskIdleHook() is either empty, sleeps for some time or sleeps until
 *   the next signal is delivered issuing a select() system call.
 * - OSTaskStkInit() prepares a ucontext_t structure on the tasks stack and
 *   adjusts the TCBs fields. The SysV calls getcontext() and makecontext()
 *   help with this procedure.
 * - OSStartHighRdy() restores the proviously made context using setcontext().
 *   Since this function is used only once it should be replaced by a call
 *   to OSCtxSw in the future.
 * - OS_CPU_SR: This type is mapped to a sigset_t. It is used to mask and 
 *   unmask signals. Since the Linux port employs critical method #3 it is
 *   used throughout the system.
 * - OS_CRITICAL_METHOD := 3; The Linux port must remember the previous 
 *   state of the signal mask.
 * - OS_ENTER_CRITICAL() is a macro that blocks SIGALRM and SIGUSR1 using
 *   the Linux syscall sigprocmask().
 * - OS_EXIT_CRITICAL() restores the previous signal mask.
 * - OS_TASK_DEF_STK_SIZE: A reasonalbe size on Linux is 2000 words. This is 
 *   mainly due to taking signals on the stack.
 * 
 * 
 * \section ext Extensions using SIGIO
 * 
 * Adding new virtual devices to this port may be done using a signal handler
 * for IO related signals from real devices and syscalls.
 *
 * For multiple sources, a vectoring table should be implemented.
 *
 * 
 * \section lic License
 * 
 * This port of microC/OS-II may be freely used for personal and educational purposes.
 * For commercial development contact Sensaco GmbH, http://sensaco.com/en/contact.php,
 * to obtain a free license and/or support.
 *
 * For the basic microC/OS-II license, please contact Micrium Inc.
 */