/*
    FreeRTOS V6.1.1 - Copyright (C) 2011 Real Time Engineers Ltd.

    ***************************************************************************
    *                                                                         *
    * If you are:                                                             *
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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 *
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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.

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*/


/* Standard includes. */
#include <stdlib.h>

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

/* Constants required to setup the initial task context. */
#define portINITIAL_SPSR				( ( portSTACK_TYPE ) 0x1f ) /* System mode, ARM mode, interrupts enabled. */
#define portTHUMB_MODE_BIT				( ( portSTACK_TYPE ) 0x20 )
#define portINSTRUCTION_SIZE			( ( portSTACK_TYPE ) 4 )
#define portNO_CRITICAL_SECTION_NESTING	( ( portSTACK_TYPE ) 0 )

/* Constants required to setup the tick ISR. */
#define portENABLE_TIMER			( ( unsigned portCHAR ) 0x01 )
#define portPRESCALE_VALUE			0x00
#define portINTERRUPT_ON_MATCH		( ( unsigned portLONG ) 0x01 )
#define portRESET_COUNT_ON_MATCH	( ( unsigned portLONG ) 0x02 )

/* Constants required to setup the VIC for the tick ISR. */
#define portTIMER_VIC_CHANNEL		( ( unsigned portLONG ) 0x0004 )
#define portTIMER_VIC_CHANNEL_BIT	( ( unsigned portLONG ) 0x0010 )
#define portTIMER_VIC_ENABLE		( ( unsigned portLONG ) 0x0020 )

/* Constants required to handle interrupts. */
#define portTIMER_MATCH_ISR_BIT		( ( unsigned portCHAR ) 0x01 )
#define portCLEAR_VIC_INTERRUPT		( ( unsigned portLONG ) 0 )

/*-----------------------------------------------------------*/

/* The code generated by the Keil compiler does not maintain separate
stack and frame pointers. The portENTER_CRITICAL macro cannot therefore
use the stack as per other ports.  Instead a variable is used to keep
track of the critical section nesting.  This variable has to be stored
as part of the task context and must be initialised to a non zero value. */

#define portNO_CRITICAL_NESTING		( ( unsigned portLONG ) 0 )
volatile unsigned portLONG ulCriticalNesting = 9999UL;

/*-----------------------------------------------------------*/

/* Setup the timer to generate the tick interrupts. */
static void prvSetupTimerInterrupt( void );

/* 
 * The scheduler can only be started from ARM mode, so 
 * vPortStartFirstSTask() is defined in portISR.c. 
 */
extern __asm void vPortStartFirstTask( void );

/*-----------------------------------------------------------*/

/* 
 * See header file for description. 
 */
portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
{
portSTACK_TYPE *pxOriginalTOS;

	/* Setup the initial stack of the task.  The stack is set exactly as 
	expected by the portRESTORE_CONTEXT() macro.

	Remember where the top of the (simulated) stack is before we place 
	anything on it. */
	pxOriginalTOS = pxTopOfStack;

	/* First on the stack is the return address - which in this case is the
	start of the task.  The offset is added to make the return address appear
	as it would within an IRQ ISR. */
	*pxTopOfStack = ( portSTACK_TYPE ) pxCode + portINSTRUCTION_SIZE;		
	pxTopOfStack--;

	*pxTopOfStack = ( portSTACK_TYPE ) 0xaaaaaaaa;	/* R14 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) pxOriginalTOS; /* Stack used when task starts goes in R13. */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0x12121212;	/* R12 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x11111111;	/* R11 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x10101010;	/* R10 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x09090909;	/* R9 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x08080808;	/* R8 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x07070707;	/* R7 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x06060606;	/* R6 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x05050505;	/* R5 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x04040404;	/* R4 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x03030303;	/* R3 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x02020202;	/* R2 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x01010101;	/* R1 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) pvParameters; /* R0 */
	pxTopOfStack--;

	/* The last thing onto the stack is the status register, which is set for
	system mode, with interrupts enabled. */
	*pxTopOfStack = ( portSTACK_TYPE ) portINITIAL_SPSR;

	if( ( ( unsigned long ) pxCode & 0x01UL ) != 0x00UL )
	{
		/* We want the task to start in thumb mode. */
		*pxTopOfStack |= portTHUMB_MODE_BIT;
	}

	pxTopOfStack--;

	/* The code generated by the Keil compiler does not maintain separate
	stack and frame pointers. The portENTER_CRITICAL macro cannot therefore
	use the stack as per other ports.  Instead a variable is used to keep
	track of the critical section nesting.  This variable has to be stored
	as part of the task context and is initially set to zero. */
	*pxTopOfStack = portNO_CRITICAL_SECTION_NESTING;

	return pxTopOfStack;
}
/*-----------------------------------------------------------*/

portBASE_TYPE xPortStartScheduler( void )
{
	/* Start the timer that generates the tick ISR. */
	prvSetupTimerInterrupt();

	/* Start the first task.  This is done from portISR.c as ARM mode must be
	used. */
	vPortStartFirstTask();

	/* Should not get here! */
	return 0;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
	/* It is unlikely that the ARM port will require this function as there
	is nothing to return to.  If this is required - stop the tick ISR then
	return back to main. */
}
/*-----------------------------------------------------------*/

#if configUSE_PREEMPTION == 0

	/* 
	 * The cooperative scheduler requires a normal IRQ service routine to 
	 * simply increment the system tick. 
	 */
	void vNonPreemptiveTick( void ) __irq;
	void vNonPreemptiveTick( void ) __irq
	{
		/* Increment the tick count - this may make a delaying task ready
		to run - but a context switch is not performed. */		
		vTaskIncrementTick();

		T0IR = portTIMER_MATCH_ISR_BIT;				/* Clear the timer event */
		VICVectAddr = portCLEAR_VIC_INTERRUPT;		/* Acknowledge the Interrupt */
	}

 #else

	/*
	 **************************************************************************
	 * The preemptive scheduler ISR is written in assembler and can be found   
	 * in the portASM.s file. This will only get used if portUSE_PREEMPTION
	 * is set to 1 in portmacro.h
	 ************************************************************************** 
	 */

	  void vPreemptiveTick( void );

#endif
/*-----------------------------------------------------------*/

static void prvSetupTimerInterrupt( void )
{
unsigned portLONG ulCompareMatch;

	/* A 1ms tick does not require the use of the timer prescale.  This is
	defaulted to zero but can be used if necessary. */
	T0PR = portPRESCALE_VALUE;

	/* Calculate the match value required for our wanted tick rate. */
	ulCompareMatch = configCPU_CLOCK_HZ / configTICK_RATE_HZ;

	/* Protect against divide by zero.  Using an if() statement still results
	in a warning - hence the #if. */
	#if portPRESCALE_VALUE != 0
	{
		ulCompareMatch /= ( portPRESCALE_VALUE + 1 );
	}
	#endif

	T0MR0 = ulCompareMatch;

	/* Generate tick with timer 0 compare match. */
	T0MCR = portRESET_COUNT_ON_MATCH | portINTERRUPT_ON_MATCH;

	/* Setup the VIC for the timer. */
	VICIntSelect &= ~( portTIMER_VIC_CHANNEL_BIT );
	VICIntEnable |= portTIMER_VIC_CHANNEL_BIT;
	
	/* The ISR installed depends on whether the preemptive or cooperative
	scheduler is being used. */
	#if configUSE_PREEMPTION == 1
	{	
		VICVectAddr0 = ( unsigned portLONG ) vPreemptiveTick;
	}
	#else
	{
		VICVectAddr0 = ( unsigned portLONG ) vNonPreemptiveTick;
	}
	#endif

	VICVectCntl0 = portTIMER_VIC_CHANNEL | portTIMER_VIC_ENABLE;

	/* Start the timer - interrupts are disabled when this function is called
	so it is okay to do this here. */
	T0TCR = portENABLE_TIMER;
}
/*-----------------------------------------------------------*/

void vPortEnterCritical( void )
{
	/* Disable interrupts as per portDISABLE_INTERRUPTS(); 							*/
	__disable_irq();

	/* Now interrupts are disabled ulCriticalNesting can be accessed 
	directly.  Increment ulCriticalNesting to keep a count of how many times
	portENTER_CRITICAL() has been called. */
	ulCriticalNesting++;
}
/*-----------------------------------------------------------*/

void vPortExitCritical( void )
{
	if( ulCriticalNesting > portNO_CRITICAL_NESTING )
	{
		/* Decrement the nesting count as we are leaving a critical section. */
		ulCriticalNesting--;

		/* If the nesting level has reached zero then interrupts should be
		re-enabled. */
		if( ulCriticalNesting == portNO_CRITICAL_NESTING )
		{
			/* Enable interrupts as per portEXIT_CRITICAL(). */
			__enable_irq();
		}
	}
}
/*-----------------------------------------------------------*/