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/*

    FreeRTOS V6.1.1 - Copyright (C) 2011 Real Time Engineers Ltd.

    ***************************************************************************

    *                                                                         *

    * If you are:                                                             *

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    *    + New to FreeRTOS,                                                   *

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    *                                                                         *

    * then take a look at the FreeRTOS books - available as PDF or paperback  *

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    *        "Using the FreeRTOS Real Time Kernel - a Practical Guide"        *

    *                  http://www.FreeRTOS.org/Documentation                  *

    *                                                                         *

    * A pdf reference manual is also available.  Both are usually delivered   *

    * to your inbox within 20 minutes to two hours when purchased between 8am *

    * and 8pm GMT (although please allow up to 24 hours in case of            *

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    ***************************************************************************

    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.

    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 and the FreeRTOS license exception along with FreeRTOS; if not it

    can be viewed here: http://www.freertos.org/a00114.html and also obtained

    by writing to Richard Barry, contact details for whom are available on the

    FreeRTOS WEB site.

    1 tab == 4 spaces!

    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.

*/

/* High speed timer test as described in main.c. */

/* Scheduler includes. */

#include "FreeRTOS.h"

/* Demo includes. */

#include "partest.h"

/* The number of interrupts to pass before we start looking at the jitter. */

#define timerSETTLE_TIME                        5

/* The maximum value the 16bit timer can contain. */

#define timerMAX_COUNT                          0xffff

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

/*

 * Measure the time between this interrupt and the previous interrupt to

 * calculate the timing jitter.  Remember the maximum value the jitter has

 * ever been calculated to be.

 */

static void prvCalculateAndStoreJitter( void );

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

/* The maximum time (in processor clocks) between two consecutive timer

interrupts so far. */

unsigned portSHORT usMaxJitter = 0;

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

void vSetupTimerTest( unsigned portSHORT usFrequencyHz )

{

        /* T2 is used to generate interrupts.  T4 is used to provide an accurate

        time measurement. */

        T2CON = 0;

        T4CON = 0;

        TMR2 = 0;

        TMR4 = 0;

        /* Timer 2 is going to interrupt at usFrequencyHz Hz. */

        PR2 = ( unsigned portSHORT ) ( configCPU_CLOCK_HZ / ( unsigned portLONG ) usFrequencyHz );

        /* Timer 4 is going to free run from minimum to maximum value. */

        PR4 = ( unsigned portSHORT ) timerMAX_COUNT;

        /* Setup timer 2 interrupt priority to be above the kernel priority so

        the timer jitter is not effected by the kernel activity. */

        IPC1bits.T2IP = configKERNEL_INTERRUPT_PRIORITY + 1;

        /* Clear the interrupt as a starting condition. */

        IFS0bits.T2IF = 0;

        /* Enable the interrupt. */

        IEC0bits.T2IE = 1;

        /* Start both timers. */

        T2CONbits.TON = 1;

        T4CONbits.TON = 1;

}

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

static void prvCalculateAndStoreJitter( void )

{

static unsigned portSHORT usLastCount = 0, usSettleCount = 0;

unsigned portSHORT usThisCount, usDifference;

        /* Capture the timer value as we enter the interrupt. */

        usThisCount = TMR4;

        if( usSettleCount >= timerSETTLE_TIME )

        {

                /* What is the difference between the timer value in this interrupt

                and the value from the last interrupt. */

                usDifference = usThisCount - usLastCount;

                /* Store the difference in the timer values if it is larger than the

                currently stored largest value.  The difference over and above the

                expected difference will give the 'jitter' in the processing of these

                interrupts. */

                if( usDifference > usMaxJitter )

                {

                        usMaxJitter = usDifference;

                }

        }

        else

        {

                /* Don't bother storing any values for the first couple of

                interrupts. */

                usSettleCount++;

        }

        /* Remember what the timer value was this time through, so we can calculate

        the difference the next time through. */

        usLastCount = usThisCount;

}

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

void __attribute__((__interrupt__, auto_psv)) _T2Interrupt( void )

{

        /* Work out the time between this and the previous interrupt. */

        prvCalculateAndStoreJitter();

        /* Clear the timer interrupt. */

        IFS0bits.T2IF = 0;

}