root/webserver/example/freeRTOSexample/Demo/Common/Minimal/semtest.c

/*
        FreeRTOS V5.4.1 - Copyright (C) 2009 Real Time Engineers Ltd.

        This file is part of the FreeRTOS distribution.

        FreeRTOS is free software; you can redistribute it and/or modify it     under 
        the terms of the GNU General Public License (version 2) as published by the 
        Free Software Foundation and modified by the FreeRTOS exception.
        **NOTE** The exception to the GPL is included to allow you to distribute a
        combined work that includes FreeRTOS without being obliged to provide the 
        source code for proprietary components outside of the FreeRTOS kernel.  
        Alternative commercial license and support terms are also available upon 
        request.  See the licensing section of http://www.FreeRTOS.org for full 
        license details.

        FreeRTOS is distributed in the hope that it will be useful,     but WITHOUT
        ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
        FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
        more details.

        You should have received a copy of the GNU General Public License along
        with FreeRTOS; if not, write to the Free Software Foundation, Inc., 59
        Temple Place, Suite 330, Boston, MA  02111-1307  USA.


        ***************************************************************************
        *                                                                         *
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        * See http://www.FreeRTOS.org/Documentation for details                   *
        *                                                                         *
        ***************************************************************************

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        Please ensure to read the configuration and relevant port sections of the
        online documentation.

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*/

/*
 * Creates two sets of two tasks.  The tasks within a set share a variable, access 
 * to which is guarded by a semaphore.
 * 
 * Each task starts by attempting to obtain the semaphore.  On obtaining a 
 * semaphore a task checks to ensure that the guarded variable has an expected 
 * value.  It then clears the variable to zero before counting it back up to the 
 * expected value in increments of 1.  After each increment the variable is checked 
 * to ensure it contains the value to which it was just set. When the starting 
 * value is again reached the task releases the semaphore giving the other task in 
 * the set a chance to do exactly the same thing.  The starting value is high 
 * enough to ensure that a tick is likely to occur during the incrementing loop.
 *
 * An error is flagged if at any time during the process a shared variable is 
 * found to have a value other than that expected.  Such an occurrence would 
 * suggest an error in the mutual exclusion mechanism by which access to the 
 * variable is restricted.
 *
 * The first set of two tasks poll their semaphore.  The second set use blocking 
 * calls.
 *
 */


#include <stdlib.h>

/* Scheduler include files. */
#include "FreeRTOS.h"
#include "task.h"
#include "semphr.h"

/* Demo app include files. */
#include "semtest.h"

/* The value to which the shared variables are counted. */
#define semtstBLOCKING_EXPECTED_VALUE           ( ( unsigned portLONG ) 0xfff )
#define semtstNON_BLOCKING_EXPECTED_VALUE       ( ( unsigned portLONG ) 0xff  )

#define semtstSTACK_SIZE                        configMINIMAL_STACK_SIZE

#define semtstNUM_TASKS                         ( 4 )

#define semtstDELAY_FACTOR                      ( ( portTickType ) 10 )

/* The task function as described at the top of the file. */
static portTASK_FUNCTION_PROTO( prvSemaphoreTest, pvParameters );

/* Structure used to pass parameters to each task. */
typedef struct SEMAPHORE_PARAMETERS
{
        xSemaphoreHandle xSemaphore;
        volatile unsigned portLONG *pulSharedVariable;
        portTickType xBlockTime;
} xSemaphoreParameters;

/* Variables used to check that all the tasks are still running without errors. */
static volatile portSHORT sCheckVariables[ semtstNUM_TASKS ] = { 0 };
static volatile portSHORT sNextCheckVariable = 0;

/*-----------------------------------------------------------*/

void vStartSemaphoreTasks( unsigned portBASE_TYPE uxPriority )
{
xSemaphoreParameters *pxFirstSemaphoreParameters, *pxSecondSemaphoreParameters;
const portTickType xBlockTime = ( portTickType ) 100;

        /* Create the structure used to pass parameters to the first two tasks. */
        pxFirstSemaphoreParameters = ( xSemaphoreParameters * ) pvPortMalloc( sizeof( xSemaphoreParameters ) );

        if( pxFirstSemaphoreParameters != NULL )
        {
                /* Create the semaphore used by the first two tasks. */
                vSemaphoreCreateBinary( pxFirstSemaphoreParameters->xSemaphore );

                if( pxFirstSemaphoreParameters->xSemaphore != NULL )
                {
                        /* Create the variable which is to be shared by the first two tasks. */
                        pxFirstSemaphoreParameters->pulSharedVariable = ( unsigned portLONG * ) pvPortMalloc( sizeof( unsigned portLONG ) );

                        /* Initialise the share variable to the value the tasks expect. */
                        *( pxFirstSemaphoreParameters->pulSharedVariable ) = semtstNON_BLOCKING_EXPECTED_VALUE;

                        /* The first two tasks do not block on semaphore calls. */
                        pxFirstSemaphoreParameters->xBlockTime = ( portTickType ) 0;

                        /* Spawn the first two tasks.  As they poll they operate at the idle priority. */
                        xTaskCreate( prvSemaphoreTest, ( signed portCHAR * ) "PolSEM1", semtstSTACK_SIZE, ( void * ) pxFirstSemaphoreParameters, tskIDLE_PRIORITY, ( xTaskHandle * ) NULL );
                        xTaskCreate( prvSemaphoreTest, ( signed portCHAR * ) "PolSEM2", semtstSTACK_SIZE, ( void * ) pxFirstSemaphoreParameters, tskIDLE_PRIORITY, ( xTaskHandle * ) NULL );
                }
        }

        /* Do exactly the same to create the second set of tasks, only this time 
        provide a block time for the semaphore calls. */
        pxSecondSemaphoreParameters = ( xSemaphoreParameters * ) pvPortMalloc( sizeof( xSemaphoreParameters ) );
        if( pxSecondSemaphoreParameters != NULL )
        {
                vSemaphoreCreateBinary( pxSecondSemaphoreParameters->xSemaphore );

                if( pxSecondSemaphoreParameters->xSemaphore != NULL )
                {
                        pxSecondSemaphoreParameters->pulSharedVariable = ( unsigned portLONG * ) pvPortMalloc( sizeof( unsigned portLONG ) );
                        *( pxSecondSemaphoreParameters->pulSharedVariable ) = semtstBLOCKING_EXPECTED_VALUE;
                        pxSecondSemaphoreParameters->xBlockTime = xBlockTime / portTICK_RATE_MS;

                        xTaskCreate( prvSemaphoreTest, ( signed portCHAR * ) "BlkSEM1", semtstSTACK_SIZE, ( void * ) pxSecondSemaphoreParameters, uxPriority, ( xTaskHandle * ) NULL );
                        xTaskCreate( prvSemaphoreTest, ( signed portCHAR * ) "BlkSEM2", semtstSTACK_SIZE, ( void * ) pxSecondSemaphoreParameters, uxPriority, ( xTaskHandle * ) NULL );
                }
        }

        /* vQueueAddToRegistry() adds the semaphore to the registry, if one is
        in use.  The registry is provided as a means for kernel aware 
        debuggers to locate semaphores and has no purpose if a kernel aware debugger
        is not being used.  The call to vQueueAddToRegistry() will be removed
        by the pre-processor if configQUEUE_REGISTRY_SIZE is not defined or is 
        defined to be less than 1. */
        vQueueAddToRegistry( ( xQueueHandle ) pxFirstSemaphoreParameters->xSemaphore, ( signed portCHAR * ) "Counting_Sem_1" );
        vQueueAddToRegistry( ( xQueueHandle ) pxSecondSemaphoreParameters->xSemaphore, ( signed portCHAR * ) "Counting_Sem_2" );
}
/*-----------------------------------------------------------*/

static portTASK_FUNCTION( prvSemaphoreTest, pvParameters )
{
xSemaphoreParameters *pxParameters;
volatile unsigned portLONG *pulSharedVariable, ulExpectedValue;
unsigned portLONG ulCounter;
portSHORT sError = pdFALSE, sCheckVariableToUse;

        /* See which check variable to use.  sNextCheckVariable is not semaphore 
        protected! */
        portENTER_CRITICAL();
                sCheckVariableToUse = sNextCheckVariable;
                sNextCheckVariable++;
        portEXIT_CRITICAL();

        /* A structure is passed in as the parameter.  This contains the shared 
        variable being guarded. */
        pxParameters = ( xSemaphoreParameters * ) pvParameters;
        pulSharedVariable = pxParameters->pulSharedVariable;

        /* If we are blocking we use a much higher count to ensure loads of context
        switches occur during the count. */
        if( pxParameters->xBlockTime > ( portTickType ) 0 )
        {
                ulExpectedValue = semtstBLOCKING_EXPECTED_VALUE;
        }
        else
        {
                ulExpectedValue = semtstNON_BLOCKING_EXPECTED_VALUE;
        }

        for( ;; )
        {
                /* Try to obtain the semaphore. */
                if( xSemaphoreTake( pxParameters->xSemaphore, pxParameters->xBlockTime ) == pdPASS )
                {
                        /* We have the semaphore and so expect any other tasks using the
                        shared variable to have left it in the state we expect to find
                        it. */
                        if( *pulSharedVariable != ulExpectedValue )
                        {
                                sError = pdTRUE;
                        }
                        
                        /* Clear the variable, then count it back up to the expected value
                        before releasing the semaphore.  Would expect a context switch or
                        two during this time. */
                        for( ulCounter = ( unsigned portLONG ) 0; ulCounter <= ulExpectedValue; ulCounter++ )
                        {
                                *pulSharedVariable = ulCounter;
                                if( *pulSharedVariable != ulCounter )
                                {
                                        sError = pdTRUE;
                                }
                        }

                        /* Release the semaphore, and if no errors have occurred increment the check
                        variable. */
                        if(     xSemaphoreGive( pxParameters->xSemaphore ) == pdFALSE )
                        {
                                sError = pdTRUE;
                        }

                        if( sError == pdFALSE )
                        {
                                if( sCheckVariableToUse < semtstNUM_TASKS )
                                {
                                        ( sCheckVariables[ sCheckVariableToUse ] )++;
                                }
                        }

                        /* If we have a block time then we are running at a priority higher
                        than the idle priority.  This task takes a long time to complete
                        a cycle (deliberately so to test the guarding) so will be starving
                        out lower priority tasks.  Block for some time to allow give lower
                        priority tasks some processor time. */
                        vTaskDelay( pxParameters->xBlockTime * semtstDELAY_FACTOR );
                }
                else
                {
                        if( pxParameters->xBlockTime == ( portTickType ) 0 )
                        {
                                /* We have not got the semaphore yet, so no point using the
                                processor.  We are not blocking when attempting to obtain the
                                semaphore. */
                                taskYIELD();
                        }
                }
        }
}
/*-----------------------------------------------------------*/

/* This is called to check that all the created tasks are still running. */
portBASE_TYPE xAreSemaphoreTasksStillRunning( void )
{
static portSHORT sLastCheckVariables[ semtstNUM_TASKS ] = { 0 };
portBASE_TYPE xTask, xReturn = pdTRUE;

        for( xTask = 0; xTask < semtstNUM_TASKS; xTask++ )
        {
                if( sLastCheckVariables[ xTask ] == sCheckVariables[ xTask ] )
                {
                        xReturn = pdFALSE;
                }

                sLastCheckVariables[ xTask ] = sCheckVariables[ xTask ];
        }

        return xReturn;
}