freertos.rar_2440FREERTOS_freertos_recursivesemaphore

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《FreeRTOS：嵌入式实时操作系统与递归信号量详解》 FreeRTOS 是一款高度可移植的、开源的实时操作系统（RTOS），专为微控制器和小型嵌入式系统设计。它以其高效、小巧且功能强大的特性，广泛应用于各种工业、消费电子以及物联网设备中。在“freertos.rar_2440 FREERTOS_freertos_recursive_semaphore_嵌入式”这个压缩包中，我们主要探讨的是FreeRTOS在2440平台上的应用以及递归信号量的概念和使用。 2440平台通常指的是Samsung公司的S3C2440微处理器，这是一款基于ARM920T内核的处理器，广泛用于嵌入式开发。在该平台上集成FreeRTOS，可以实现复杂的任务调度和实时响应，提高系统的整体性能。 FreeRTOS的核心是任务调度机制，它能有效地管理多个并发任务，并根据优先级进行调度。在FreeRTOS中，信号量是一种多任务间通信和同步的重要工具，用于保护共享资源或协调任务间的操作。递归信号量（recursive semaphore）是FreeRTOS提供的一种特殊类型的信号量，它允许一个任务在已经持有信号量的情况下再次请求同一信号量，而不被阻塞。这种机制在处理嵌套调用或者需要多次访问同一资源的情景下非常有用。在压缩包内的文件中，如"xSemaphoreTakeRecursive.html"和"xSemaphoreGiveRecursive.html"，详细介绍了如何获取和释放递归信号量。`xSemaphoreTakeRecursive()`函数用于尝试获取信号量，如果当前信号量未被占用或者由调用任务持有，那么函数会返回成功并增加信号量的计数值。而`xSemaphoreGiveRecursive()`函数则是用来释放信号量，它会检查任务是否是信号量的所有者，如果是，则递减计数值，直到计数值为零时，其他等待该信号量的任务才可能被唤醒。除此之外，其他文件如"crrecisr.html"和"crsendisr.html"可能涉及到中断上下文中的递归信号量操作。在中断服务例程（ISR）中，由于不能阻塞当前任务，因此使用递归信号量需要特别注意。FreeRTOS提供了在ISR中安全操作信号量的API，但需谨慎处理，避免死锁和优先级反转问题。此外，文件"a00117.html"中的"xQueueSendToBack()"函数展示了如何将数据发送到队列的末尾，这是另一种任务间通信的方式，可以用于实现异步操作和数据传递。文件"a00122.html"可能涉及递归信号量的释放，即`xSemaphoreGiveRecursive()`的使用场景和最佳实践。这个压缩包提供了关于FreeRTOS在2440平台上的实际应用以及递归信号量使用的一系列教程和参考。通过深入学习这些资料，开发者可以更好地理解和利用FreeRTOS的实时性和强大的并发能力，以构建高效的嵌入式系统。

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freertos.rar （56个子文件）

CreateCounting.html 4KB

xQueuePeek.html 5KB

a00125.html 5KB

xSemaphoreTakeRecursive.html 6KB

a00123.html 4KB

crqueuerec.html 5KB

a00119.html 4KB

a00126.html 3KB

a00130.html 3KB

Stacks-and-stack-overflow-checking.html 5KB

CreateMutex.html 4KB

a00121.html 4KB

a00111.html 6KB

crrecisr.html 6KB

a00129.html 3KB

a00019.html 2KB

a00122.html 5KB

crsendisr.html 6KB

a00131.html 3KB

crdelay.html 3KB

xQueueSendToBack.html 5KB

a00110.html 15KB

taskresumefromisr.html 4KB

a00020.html 3KB

a00127.html 3KB

upgrading.html 4KB

a00117.html 5KB

xQueueSendToBackFromISR.html 4KB

a00106.html 2KB

a00118.html 5KB

croutineapi.html 1KB

a00134.html 4KB

Index.html 2KB

a00112.html 2KB

a00113.html 2KB

a00116.html 4KB

a00133.html 3KB

xSemaphoreGiveRecursive.html 5KB

xSemaphoreCreateRecursiveMutex.html 3KB

a00124.html 5KB

a00132.html 3KB

a00128.html 3KB

api.html 4KB

xTaskCallApplicationTaskHook.html 4KB

crschedule.html 2KB

vtaskdelayuntil.html 5KB

a00018.html 3KB

crqueuesend.html 5KB

a00135.html 4KB

a00109.html 1KB

a00021.html 6KB

crcreate.html 5KB

xQueueSendToFrontFromISR.html 4KB

vTaskSetApplicationTag.html 5KB

xQueueSendToFront.html 5KB

a00120.html 5KB

<head> <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1"> <META name="description" content="FreeRTOS is a portable, open source, mini Real Time kernel. A free RTOS for small embedded systems"> <META name="keywords" content="8051, 8052, Free RTOS, royalty free, RTOS, free, RTOS free, open source, real time, embedded, FreeRTOS, source code, AVR, GNU, PIC, PIC18, development tools"> <title>FreeRTOS - A FREE Open Source RTOS for small real time embedded systems</title><link rel="stylesheet" href="doxygen.css"><style type="text/css"></style> </head> <font face="Arial"> <body><div align="right"><font face="arial"><small><a href="http://www.freertos.org/" target="_top">Homepage</a></small>  </font></div> </BODY>  <h1>Customisation<br> <small> [<a class="el" href="a00109.html">Configuration</a>]</small></h1> A number of configurable parameters exist that allow the FreeRTOS kernel to be tailored to your particular application. These items are located in a file called FreeRTOSConfig.h. Each demo application included in the FreeRTOS source code download has its own FreeRTOSConfig.h file. Here is a typical example, followed by an explanation of each parameter: <p> <font face="courier"><pre> #ifndef FREERTOS_CONFIG_H #define FREERTOS_CONFIG_H /* Here is a good place to include header files that are required across your application. */ #include "something.h" #define configUSE_PREEMPTION 1 #define configUSE_IDLE_HOOK 0 #define configUSE_TICK_HOOK 0 #define configCPU_CLOCK_HZ 58982400 #define configTICK_RATE_HZ 250 #define configMAX_PRIORITIES 5 #define configMINIMAL_STACK_SIZE 128 #define configTOTAL_HEAP_SIZE 10240 #define configMAX_TASK_NAME_LEN 16 #define configUSE_TRACE_FACILITY 0 #define configUSE_16_BIT_TICKS 0 #define configIDLE_SHOULD_YIELD 1 #define configUSE_MUTEXES 0 #define configUSE_RECURSIVE_MUTEXES 0 #define configUSE_COUNTING_SEMAPHORES 0 #define configUSE_ALTERNATIVE_API 0 #define configCHECK_FOR_STACK_OVERFLOW 0 #define INCLUDE_vTaskPrioritySet 1 #define INCLUDE_uxTaskPriorityGet 1 #define INCLUDE_vTaskDelete 1 #define INCLUDE_vTaskCleanUpResources 0 #define INCLUDE_vTaskSuspend 1 #define INCLUDE_vResumeFromISR 1 #define INCLUDE_vTaskDelayUntil 1 #define INCLUDE_vTaskDelay 1 #define INCLUDE_xTaskGetSchedulerState 1 #define INCLUDE_xTaskGetCurrentTaskHandle 1 #define INCLUDE_uxTaskGetStackHighWaterMark 0 #define configUSE_CO_ROUTINES 0 #define configMAX_CO_ROUTINE_PRIORITIES 1 #define configKERNEL_INTERRUPT_PRIORITY [dependent of processor] #define configMAX_SYSCALL_INTERRUPT_PRIORITY [dependent on processor and application] #endif /* FREERTOS_CONFIG_H */ </pre></font> <p> <hr> <h2>'config' Parameters</h2> <h3>configUSE_PREEMPTION</h3> Set to 1 to use the preemptive kernel, or 0 to use the cooperative kernel. <p> <br> <h3>configUSE_IDLE_HOOK</h3> Set to 1 if you wish to use an <a href="http://www.freertos.org/a00015.html#IdleHook">idle hook</a>, or 0 to omit an idle hook. <p> <br> <h3>configUSE_TICK_HOOK</h3> Set to 1 if you wish to use an <a href="http://www.freertos.org/a00016.html#TickHook">tick hook</a>, or 0 to omit an tick hook. <p> <br> <h3>configCPU_CLOCK_HZ</h3> Enter the frequency in Hz at which the <i>internal</i> processor core will be executing. This value is required in order to correctly configure timer peripherals. <p> <br> <h3>configTICK_RATE_HZ</h3> The frequency of the RTOS tick interrupt. <p> The tick interrupt is used to measure time. Therefore a higher tick frequency means time can be measured to a higher resolution. However, a high tick frequency also means that the kernel will use more CPU time so be less efficient. The RTOS demo applications all use a tick rate of 1000Hz. This is used to test the kernel and is higher than would normally be required. <p> More than one task can share the same priority. The kernel will share processor time between tasks of the same priority by switching between the tasks during each RTOS tick. A high tick rate frequency will therefore also have the effect of reducing the 'time slice' given to each task. <p> <br> <h3>configMAX_PRIORITIES</h3> The number of <a href="http://www.freertos.org/a00015.html#Prior">priorities</a> available to the application tasks. Any number of tasks can share the same priority. Co-routines are prioritised separately - see configMAX_CO_ROUTINE_PRIORITIES. <p> Each available priority consumes RAM within the kernel so this value should not be set any higher than actually required by your application. <p> <br> <h3>configMINIMAL_STACK_SIZE</h3> The size of the stack used by the idle task. Generally this should not be reduced from the value set in the FreeRTOSConfig.h file provided with the demo application for the port you are using. <p> <br> <h3>configTOTAL_HEAP_SIZE</h3> The total amount of RAM available to the kernel. <p> This value will only be used if your application makes use of one of the sample memory allocation schemes provided in the FreeRTOS source code download. See the <a href="http://www.freertos.org/a00111.html">memory configuration</a> section for further details. <p> <br> <h3>configMAX_TASK_NAME_LEN</h3> The maximum permissible length of the descriptive name given to a task when the task is created. The length is specified in the number of characters <i>including</i> the NULL termination byte. <p> <br> <h3>configUSE_TRACE_FACILITY</h3> Set to 1 if you wish the trace visualisation functionality to be available, or 0 if the trace functionality is not going to be used. If you use the trace functionality a trace buffer must also be provided. <p> <br> <h3>configUSE_16_BIT_TICKS</h3> Time is measured in 'ticks' - which is the number of times the tick interrupt has executed since the kernel was started. The tick count is held in a variable of type portTickType. <p> Defining configUSE_16_BIT_TICKS as 1 causes portTickType to be defined (typedef'ed) as an unsigned 16bit type. Defining configUSE_16_BIT_TICKS as 0 causes portTickType to be defined (typedef'ed) as an unsigned 32bit type. <p> Using a 16 bit type will greatly improve performance on 8 and 16 bit architectures, but limits the maximum specifiable time period to 65535 'ticks'. Therefore, assuming a tick frequency of 250Hz, the maximum time a task can delay or block when a 16bit counter is used is 262 seconds, compared to 17179869 seconds when using a 32bit counter. <p> <br> <h3>configIDLE_SHOULD_YIELD</h3> This parameter controls the behaviour of tasks at the idle priority. It only has an effect if: <ol> <li>The preemptive scheduler is being used.</li> <li>The users application creates tasks that run at the idle priority.</li> </ol> Tasks that share the same priority will time slice. Assuming none of the tasks get preempted, it might be assumed that each task of at a given priority will be allocated an equal amount of processing time - and if the shared priority is above the idle priority then this is indeed the case. <p> When tasks share the idle priority the behaviour can be slightly different. When configIDLE_SHOULD_YIELD is set to 1 the idle task will yield immediately should any other task at the idle priority be ready to run. This ensures the minimum amount of time is spent in the idle task when application tasks are available for scheduling. This behaviour can however have undesirable effects (depending on the needs of your application) as depicted below: <div align="center"><img src="idl

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