semtest.c

Show hou use semaphores in RTL-ARM

/* 
 ********************************************************************
 * Project:    GNU-Port FreeRTOS Port
 * File:    	semtest.c
 *
 * System:   	ARM7TDMI-S 32 Bit (LPC2378)
 * Compiler:  	GCC 4.0.3
 *
 * Date:      	2006-11-17
 * Author:    	Grohmann
 *
 * Rights:    	Hitex Development Tools GmbH
 *            	Greschbachstr. 12
 *            	D-76229 Karlsruhe
 ********************************************************************
 * Description:
 *
 * This file is part of the GNU FreeRTOS Port
 * The code is based on the FreeRTOS originated by Richard Barry
 * This is a small implementation preemtive and semaphore task. 
 * The application runs in ARM mode with high optimization level.
 *	
 ********************************************************************
 * History:
 *
 *  Revision 1.0    2006/11/17      Gn
 *     Initial revision 
 ********************************************************************
 * This is a preliminary version.
 *
 * WARRANTY:  HITEX warrants that the media on which the SOFTWARE is 
 * furnished is free from defects in materials and workmanship under 
 * normal use and service for a period of ninety (90) days. HITEX entire
 * liability and your exclusive remedy shall be the replacement of the 
 * SOFTWARE if the media is defective. This Warranty is void if failure
 * of the media resulted from unauthorized modification, accident, abuse,
 * or misapplication.
 *
 * DISCLAIMER:  OTHER THAN THE ABOVE WARRANTY, THE SOFTWARE IS FURNISHED
 * "AS IS" WITHOUT WARRANTY OF ANY KIND. HITEX DISCLAIMS ALL OTHER WARRANTIES,
 * EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 *
 * NEITHER HITEX NOR ITS AFFILIATES SHALL BE LIABLE FOR ANY DAMAGES ARISING
 * OUT OF THE USE OF OR INABILITY TO USE THE SOFTWARE, INCLUDING DAMAGES FOR
 * LOSS OF PROFITS, BUSINESS INTERRUPTION, OR ANY SPECIAL, INCIDENTAL, INDIRECT
 * OR CONSEQUENTIAL DAMAGES EVEN IF HITEX HAS BEEN ADVISED OF THE POSSIBILITY 
 * OF SUCH DAMAGES.
 ********************************************************************/

/**
 * 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.
 *
 * \page SemTestC semtest.c
 * \ingroup DemoFiles
 * <HR>
 */

#include <stdlib.h>

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

/* Demo app include files. */
#include "semtest.h"
#include "print.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 void prvSemaphoreTest( void *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;

/* Strings to print if USE_STDIO is defined. */
const portCHAR * const pcPollingSemaphoreTaskError = "Guarded shared variable in unexpected state.\r\n";
const portCHAR * const pcSemaphoreTaskStart = "Guarded shared variable task started.\r\n";

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

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, "PolSEM1", semtstSTACK_SIZE, ( void * ) pxFirstSemaphoreParameters, tskIDLE_PRIORITY, ( xTaskHandle * ) NULL );
			xTaskCreate( prvSemaphoreTest, "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, "BlkSEM1", semtstSTACK_SIZE, ( void * ) pxSecondSemaphoreParameters, uxPriority, ( xTaskHandle * ) NULL );
			xTaskCreate( prvSemaphoreTest, "BlkSEM2", semtstSTACK_SIZE, ( void * ) pxSecondSemaphoreParameters, uxPriority, ( xTaskHandle * ) NULL );
		}
	}
}
/*-----------------------------------------------------------*/

static void prvSemaphoreTest( void *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();

	/* Queue a message for printing to say the task has started. */
	vPrintDisplayMessage( &pcSemaphoreTaskStart );

	/* 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 )
			{
				vPrintDisplayMessage( &pcPollingSemaphoreTaskError );
				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 )
				{
					if( sError == pdFALSE )
					{
						vPrintDisplayMessage( &pcPollingSemaphoreTaskError );
					}
					sError = pdTRUE;
				}
			}

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