root/Examples_CP-JR_ARM7_LPC2368/FreeRTOS_Book/Source-Code-For-Examples/Examples/Example013/main.c

/*
        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.

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        Please ensure to read the configuration and relevant port sections of the
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*/

/* 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 xCountingSemaphore;

int main( void )
{
    /* Before a semaphore is used it must be explicitly created.  In this example
        a counting semaphore is created.  The semaphore is created to have a maximum
        count value of 10, and an initial count value of 0. */
    xCountingSemaphore = xSemaphoreCreateCounting( 10, 0 );

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

        /* Check the semaphore was created successfully. */
        if( xCountingSemaphore != 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( xCountingSemaphore, 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 multiple times.  The first will unblock the handler
        task, the following 'gives' are to demonstrate that the semaphore latches
        the events to allow the handler task to process them in turn without any 
        events getting lost.  This simulates multiple interrupts being taken by the
        processor, even though in this case the events are simulated within a single
        interrupt occurrence.*/
        xSemaphoreGiveFromISR( xCountingSemaphore, &xHigherPriorityTaskWoken );
        xSemaphoreGiveFromISR( xCountingSemaphore, &xHigherPriorityTaskWoken );
        xSemaphoreGiveFromISR( xCountingSemaphore, &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();
        }
}