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 "queue.h"
#include "portasm.h"

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

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

/* The tasks to be created. */
static void vIntegerGenerator( void *pvParameters );
static void vStringPrinter( 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 );


unsigned long ulNext = 0;
unsigned long ulCount;
unsigned long ul[ 100 ];

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

/* Declare two variables of type xQueueHandle.  One queue will be read from
within an ISR, the other will be written to from within an ISR. */
xQueueHandle xIntegerQueue, xStringQueue;

int main( void )
{
    /* Before a queue can be used it must first be created.  Create both queues
	used by this example.  One queue can hold variables of type unsigned long, 
	the other queue can hold variables of type char*.  Both queues can hold a 
	maximum of 10 items.  A real application should check the return values to 
	ensure the queues have been successfully created. */
    xIntegerQueue = xQueueCreate( 10, sizeof( unsigned long ) );
	xStringQueue = xQueueCreate( 10, sizeof( char * ) );

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

	/* Create the task that uses a queue to pass integers to the interrupt service
	routine.  The task is created at priority 1. */
	xTaskCreate( vIntegerGenerator, "IntGen", 1000, NULL, 1, NULL );

	/* Create the task that prints out the strings sent to it from the interrupt
	service routine.  This task is created at the higher priority of 2. */
	xTaskCreate( vStringPrinter, "String", 1000, NULL, 2, 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 vIntegerGenerator( void *pvParameters )
{
portTickType xLastExecutionTime;
unsigned portLONG ulValueToSend = 0;
int i;

	/* Initialize the variable used by the call to vTaskDelayUntil(). */
	xLastExecutionTime = xTaskGetTickCount();

	for( ;; )
	{
		/* This is a periodic task.  Block until it is time to run again.
		The task will execute every 200ms. */
		vTaskDelayUntil( &xLastExecutionTime, 200 / portTICK_RATE_MS );

		/* Send an incrementing number to the queue five times.  These will be 
		read from the queue by the interrupt service routine.  A block time is 
		not specified. */
		for( i = 0; i < 5; i++ )
		{
			xQueueSendToBack( xIntegerQueue, &ulValueToSend, 0 );
			ulValueToSend++;
		}

		/* Force an interrupt so the interrupt service routine can read the
		values from the queue. */
		vPrintString( "Generator task - About to generate an interrupt.\r\n" );
		__asm{ int 0x82 } 
		vPrintString( "Generator task - Interrupt generated.\r\n\r\n\r\n" );
	}
}
/*-----------------------------------------------------------*/

static void vStringPrinter( void *pvParameters )
{
char *pcString;

	for( ;; )
	{
		/* Block on the queue to wait for data to arrive. */
		xQueueReceive( xStringQueue, &pcString, portMAX_DELAY );

		/* Print out the string received. */
		vPrintString( pcString );
	}
}
/*-----------------------------------------------------------*/

static void __interrupt __far vExampleInterruptHandler( void )
{
static portBASE_TYPE xHigherPriorityTaskWoken;
static unsigned long ulReceivedNumber;

/* The strings are declared static const to ensure they are not allocated to the
interrupt service routine stack, and exist even when the interrupt service routine
is not executing. */
static const char *pcStrings[] =
{
	"String 0\r\n",
	"String 1\r\n",
	"String 2\r\n",
	"String 3\r\n"
};

	xHigherPriorityTaskWoken = pdFALSE;

	/* Loop until the queeu is empty. */
	while( xQueueReceiveFromISR( xIntegerQueue, &ulReceivedNumber, &xHigherPriorityTaskWoken ) != errQUEUE_EMPTY )
	{
		/* Truncate the received value to the last two bits (values 0 to 3 inc.), then
		send the string	that corresponds to the truncated value to the other
		queue. */
		ulReceivedNumber &= 0x03;
		xQueueSendToBackFromISR( xStringQueue, &pcStrings[ ulReceivedNumber ], &xHigherPriorityTaskWoken );
	}

	/* Did receiving on a queue or sending on a queue unblock a task that has a
	priority higher than the currently executing task?  If so, force a context
	switch here. */
	if( xHigherPriorityTaskWoken == pdTRUE )
	{
		/* 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();
	}
}