FreeRTOS Tutorial - Revision history

Proj user22: /* Binary Semaphore */

2019-11-26T19:46:17Z

‎Binary Semaphore

2019-11-26T19:43:24Z

‎Mutex

2019-11-26T19:43:08Z

‎Semaphores

2016-08-15T04:58:55Z

‎Screencast

2016-08-15T04:40:22Z

2016-08-12T21:01:02Z

‎Screencast

2016-08-12T21:00:46Z

‎Screencast

2014-03-05T16:29:43Z

2014-03-05T16:28:48Z

2013-09-16T17:14:45Z

‎Introduction

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 ==== Binary Semaphore ====
-Binary semaphore can also be used like a mutex, but binary semaphore doesn't provide priority inversion mechanism.  Binary semaphores are better suited for helper tasks for interrupts.  For example, if you have an interrupt and you don't want to do a lot of processing inside the interrupt, you can use a helper task.  To accomplish this, you can perform a semaphore give operation inside the interrupt, and a dedicated ask will sleep or block on '''xSemaphoreGet()''' operation.
+Binary semaphore can also be used like a mutex, but binary semaphore doesn't provide priority inversion mechanism.  Binary semaphores are better suited for helper tasks for interrupts.  For example, if you have an interrupt and you don't want to do a lot of processing inside the interrupt, you can use a helper task.  To accomplish this, you can perform a semaphore give operation inside the interrupt, and a dedicated task will sleep or block on '''xSemaphoreTake()''' operation.
 <syntaxhighlight lang="c">

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 ==== Mutex ====
-One of the best example of a mutex is to guard a resource or a door with a key.  For instance, let's say you have an SPI BUS, and only one task should use it at a time.  Mutex provides mutual exclusion with [http://en.wikipedia.org/wiki/Priority_inversion priority inversion mechanism].  Mutex will only allow ONE task to get past '''xSemaphoreGet()''' operation and other tasks will be put to sleep if they reach this function at the same time.
+One of the best example of a mutex is to guard a resource or a door with a key.  For instance, let's say you have an SPI BUS, and only one task should use it at a time.  Mutex provides mutual exclusion with [http://en.wikipedia.org/wiki/Priority_inversion priority inversion mechanism].  Mutex will only allow ONE task to get past '''xSemaphoreTake()''' operation and other tasks will be put to sleep if they reach this function at the same time.
 <syntaxhighlight lang="c">

@@ Line 261: / Line 261: @@
+{
      while(1) {
-         if(xSemaphoreGet(spi_bus_lock, 1000)) {
+         if(xSemaphoreTake(spi_bus_lock, 1000)) {
              // Use Guarded Resource
@@ Line 272: / Line 272: @@
+{
      while(1) {
-         if(xSemaphoreGet(spi_bus_lock, 1000)) {
+         if(xSemaphoreTake(spi_bus_lock, 1000)) {
              // Use Guarded Resource
@@ Line 282: / Line 282: @@
 </syntaxhighlight>
-In the code above, only ONE task will enter its xSemaphoreGet() branch.  If both tasks execute the statement at the same time, one will get the mutex, the other task will sleep until the mutex is returned by the task that was able to obtain it in the first place.
+In the code above, only ONE task will enter its xSemaphoreTake() branch.  If both tasks execute the statement at the same time, one will get the mutex, the other task will sleep until the mutex is returned by the task that was able to obtain it in the first place.
 ==== Binary Semaphore ====
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 <br/>
 == FAQ ==
 *  '''I wrote my own version of Queue, I don't want to use FreeRTOS queue since it is not efficient'''

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 *: '''[https://www.youtube.com/watch?v=31g6_uJ4kdE FreeRTOS Event Groups]'''
 *:  '''[https://www.youtube.com/watch?v=Rf-yobhAFy0 FreeRTOS Queue Set]'''
-*:  '''[https://www.youtube.com/watch?v=g8XIeNdAUBQ FreeRTOS Trace Analyzer]'''
+*:  '''[https://www.youtube.com/watch?v=-FX2LBN1bhI FreeRTOS Trace Analyzer]'''
 <br/>

@@ Line 21: / Line 21: @@
 *: '''[https://www.youtube.com/watch?v=31g6_uJ4kdE FreeRTOS Event Groups]'''
 *:  '''[https://www.youtube.com/watch?v=Rf-yobhAFy0 FreeRTOS Queue Set]'''
+*:  '''[https://www.youtube.com/watch?v=g8XIeNdAUBQ FreeRTOS Trace Analyzer]'''
 <br/>

@@ Line 20: / Line 20: @@
 *  Other FreeRTOS Modules:
 *: '''[https://www.youtube.com/watch?v=31g6_uJ4kdE FreeRTOS Event Groups]'''
-*  '''[https://www.youtube.com/watch?v=Rf-yobhAFy0 FreeRTOS Queue Set]'''
+*:  '''[https://www.youtube.com/watch?v=Rf-yobhAFy0 FreeRTOS Queue Set]'''

@@ Line 18: / Line 18: @@
 *:  Use this tutorial after mastering the basic FreeRTOS concepts
 *:  The source code is included in '''SJSU_Dev''' development package.
 <br/>

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 <syntaxhighlight lang="c">
 // In main(), initialize your Mutex:
-xSemaphoreHandle spi_bus_lock = xSemaphoreCreateMutex();
+SemaphoreHandle_t spi_bus_lock = xSemaphoreCreateMutex();
 void task_one()
@@ Line 285: / Line 285: @@
 <syntaxhighlight lang="c">
 // Somewhere in main() :
-xSemaphoreHandle event_signal;
+SemaphoreHandle_t event_signal;
 vSemaphoreCreateBinary( event_signal ); // Create the semaphore
 xSemaphoreTake(event_signal, 0);        // Take semaphore after creating it.

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 // Global Queue Handle
-xQueueHandle qh = 0;
+QueueHandle_t qh = 0;
 void task_tx(void* p)

@@ Line 1: / Line 1: @@
 == Introduction ==
-This article is about learning FreeRTOS.  The FreeRTOS '''sample''' project running on SJ-One board is used as reference, but any FreeRTOS project on any controller can benefit from this article.
+This article is about learning FreeRTOS.  The FreeRTOS '''sample''' project running on '''[[SJ One Board]]''' is used as reference, but any FreeRTOS project on any controller can benefit from this article.
 Notes about the FreeRTOS Sample Project: