main.c

FreeRTOS source code as bundled with the book "Using FreeRTOS Real-Time Kernel - A Practical Approac

/*
	FreeRTOS.org V5.0.4 - Copyright (C) 2003-2008 Richard Barry.

	This file is part of the FreeRTOS.org distribution.

	FreeRTOS.org is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation; either version 2 of the License, or
	(at your option) any later version.

	FreeRTOS.org 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.org; if not, write to the Free Software
	Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

	A special exception to the GPL can be applied should you wish to distribute
	a combined work that includes FreeRTOS.org, without being obliged to provide
	the source code for any proprietary components.  See the licensing section 
	of http://www.FreeRTOS.org for full details of how and when the exception
	can be applied.

    ***************************************************************************
    ***************************************************************************
    *                                                                         *
    * SAVE TIME AND MONEY!  We can port FreeRTOS.org to your own hardware,    *
    * and even write all or part of your application on your behalf.          *
    * See http://www.OpenRTOS.com for details of the services we provide to   *
    * expedite your project.                                                  *
    *                                                                         *
    ***************************************************************************
    ***************************************************************************

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

	http://www.FreeRTOS.org - Documentation, latest information, license and 
	contact details.

	http://www.SafeRTOS.com - A version that is certified for use in safety 
	critical systems.

	http://www.OpenRTOS.com - Commercial support, development, porting, 
	licensing and training services.
*/

/* FreeRTOS.org includes. */
#include "FreeRTOS.h"
#include "task.h"
#include "semphr.h"
#include "portasm.h"

/* Demo includes. */
#include "basic_io.h"

/* Compiler includes. */
#include <dos.h>

/* The tasks to be created. */
static void vHandlerTask( void *pvParameters );
static void vPeriodicTask( void *pvParameters );

/* The service routine for the interrupt.  This is the interrupt that the task 
will be synchronized with. */
static void __interrupt __far vExampleInterruptHandler( void );

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

/* Declare a variable of type xSemaphoreHandle.  This is used to reference the
semaphore that is used to synchronize a task with an interrupt. */
xSemaphoreHandle xBinarySemaphore;


int main( void )
{
    /* Before a semaphore is used it must be explicitly created.  In this example
	a binary semaphore is created. */
    vSemaphoreCreateBinary( xBinarySemaphore );

	/* Install the interrupt handler. */
	_dos_setvect( 0x82, vExampleInterruptHandler );

	/* Check the semaphore was created successfully. */
	if( xBinarySemaphore != NULL )
	{
		/* Create the 'handler' task.  This is the task that will be synchronized
		with the interrupt.  The handler task is created with a high priority to
		ensure it runs immediately after the interrupt exits.  In this case a 
		priority of 3 is chosen. */
		xTaskCreate( vHandlerTask, "Handler", 1000, NULL, 3, NULL );

		/* Create the task that will periodically generate a software interrupt. 
		This is created with a priority below the handler task to ensure it will
		get preempted each time the handler task exist the Blocked state. */
		xTaskCreate( vPeriodicTask, "Periodic", 1000, NULL, 1, NULL );

		/* Start the scheduler so the created tasks start executing. */
		vTaskStartScheduler();
	}
		
    /* If all is well we will never reach here as the scheduler will now be
    running the tasks.  If we do reach here then it is likely that there was 
    insufficient heap memory available for a resource to be created. */
	for( ;; );
	return 0;
}
/*-----------------------------------------------------------*/

static void vHandlerTask( void *pvParameters )
{
	/* As per most tasks, this task is implemented within an infinite loop. */
	for( ;; )
	{
		/* Use the semaphore to wait for the event.  The semaphore was created
		before the scheduler was started so before this task ran for the first
		time.  The task blocks indefinitely meaning this function call will only
		return once the semaphore has been successfully obtained - so there is no
		need to check the returned value. */
		xSemaphoreTake( xBinarySemaphore, portMAX_DELAY );

		/* To get here the event must have occurred.  Process the event (in this
		case we just print out a message). */
		vPrintString( "Handler task - Processing event.\r\n" );
	}
}
/*-----------------------------------------------------------*/

static void vPeriodicTask( void *pvParameters )
{
	/* As per most tasks, this task is implemented within an infinite loop. */
	for( ;; )
	{
		/* This task is just used to 'simulate' an interrupt.  This is done by
		periodically generating a software interrupt. */
		vTaskDelay( 500 / portTICK_RATE_MS );

		/* Generate the interrupt, printing a message both before hand and 
		afterwards so the sequence of execution is evident from the output. */
		vPrintString( "Perodic task - About to generate an interrupt.\r\n" );
		__asm{ int 0x82 } 
		vPrintString( "Periodic task - Interrupt generated.\r\n\r\n\r\n" );
	}
}
/*-----------------------------------------------------------*/

static void __interrupt __far vExampleInterruptHandler( void )
{
static portBASE_TYPE xHigherPriorityTaskWoken;

	xHigherPriorityTaskWoken = pdFALSE;

	/* 'Give' the semaphore to unblock the task. */
	xSemaphoreGiveFromISR( xBinarySemaphore, &xHigherPriorityTaskWoken );

	if( xHigherPriorityTaskWoken == pdTRUE )
	{
		/* Giving the semaphore unblocked a task, and the priority of the
		unblocked task is higher than the currently running task - force
		a context switch to ensure that the interrupt returns directly to
		the unblocked (higher priority) task.

		NOTE: The syntax for forcing a context switch is different depending
		on the port being used.  Refer to the examples for the port you are
		using for the correct method to use! */
		portSWITCH_CONTEXT();
	}
}