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    ***************************************************************************
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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.

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    ***************************************************************************
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*/

/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the ARM CM3 port.
 *----------------------------------------------------------*/

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

#ifndef configKERNEL_INTERRUPT_PRIORITY
	#define configKERNEL_INTERRUPT_PRIORITY 255
#endif

#if configMAX_SYSCALL_INTERRUPT_PRIORITY == 0
	#error configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to 0.  See http://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html
#endif

#ifndef configSYSTICK_CLOCK_HZ
	#define configSYSTICK_CLOCK_HZ configCPU_CLOCK_HZ
#endif

/* The __weak attribute does not work as you might expect with the Keil tools
so the configOVERRIDE_DEFAULT_TICK_CONFIGURATION constant must be set to 1 if
the application writer wants to provide their own implementation of
vPortSetupTimerInterrupt().  Ensure configOVERRIDE_DEFAULT_TICK_CONFIGURATION
is defined. */
#ifndef configOVERRIDE_DEFAULT_TICK_CONFIGURATION
	#define configOVERRIDE_DEFAULT_TICK_CONFIGURATION 0
#endif

/* Constants required to manipulate the core.  Registers first... */
#define portNVIC_SYSTICK_CTRL_REG			( * ( ( volatile unsigned long * ) 0xe000e010 ) )
#define portNVIC_SYSTICK_LOAD_REG			( * ( ( volatile unsigned long * ) 0xe000e014 ) )
#define portNVIC_SYSTICK_CURRENT_VALUE_REG	( * ( ( volatile unsigned long * ) 0xe000e018 ) )
#define portNVIC_SYSPRI2_REG				( * ( ( volatile unsigned long * ) 0xe000ed20 ) )
/* ...then bits in the registers. */
#define portNVIC_SYSTICK_CLK_BIT			( 1UL << 2UL )
#define portNVIC_SYSTICK_INT_BIT			( 1UL << 1UL )
#define portNVIC_SYSTICK_ENABLE_BIT			( 1UL << 0UL )
#define portNVIC_SYSTICK_COUNT_FLAG_BIT		( 1UL << 16UL )
#define portNVIC_PENDSVCLEAR_BIT 			( 1UL << 27UL )
#define portNVIC_PEND_SYSTICK_CLEAR_BIT		( 1UL << 25UL )

#define portNVIC_PENDSV_PRI					( ( ( unsigned long ) configKERNEL_INTERRUPT_PRIORITY ) << 16UL )
#define portNVIC_SYSTICK_PRI				( ( ( unsigned long ) configKERNEL_INTERRUPT_PRIORITY ) << 24UL )

/* Constants required to check the validity of an interrupt prority. */
#define portFIRST_USER_INTERRUPT_NUMBER		( 16 )
#define portNVIC_IP_REGISTERS_OFFSET_16 	( 0xE000E3F0 )
#define portAIRCR_REG						( * ( ( volatile unsigned long * ) 0xE000ED0C ) )
#define portPRIORITY_GROUP_MASK				( 0x07UL << 8UL )

/* Constants required to set up the initial stack. */
#define portINITIAL_XPSR			( 0x01000000 )

/* Constants used with memory barrier intrinsics. */
#define portSY_FULL_READ_WRITE		( 15 )

/* The systick is a 24-bit counter. */
#define portMAX_24_BIT_NUMBER				( 0xffffffUL )

/* A fiddle factor to estimate the number of SysTick counts that would have
occurred while the SysTick counter is stopped during tickless idle
calculations. */
#define portMISSED_COUNTS_FACTOR			( 45UL )

/* Each task maintains its own interrupt status in the critical nesting
variable. */
static unsigned portBASE_TYPE uxCriticalNesting = 0xaaaaaaaa;

/*
 * Setup the timer to generate the tick interrupts.  The implementation in this
 * file is weak to allow application writers to change the timer used to
 * generate the tick interrupt.
 */
void vPortSetupTimerInterrupt( void );

/*
 * Exception handlers.
 */
void xPortPendSVHandler( void );
void xPortSysTickHandler( void );
void vPortSVCHandler( void );

/*
 * Start first task is a separate function so it can be tested in isolation.
 */
static void prvStartFirstTask( void );

/*-----------------------------------------------------------*/

/*
 * The number of SysTick increments that make up one tick period.
 */
#if configUSE_TICKLESS_IDLE == 1
	static unsigned long ulTimerCountsForOneTick = 0;
#endif /* configUSE_TICKLESS_IDLE */

/*
 * The maximum number of tick periods that can be suppressed is limited by the
 * 24 bit resolution of the SysTick timer.
 */
#if configUSE_TICKLESS_IDLE == 1
	static unsigned long xMaximumPossibleSuppressedTicks = 0;
#endif /* configUSE_TICKLESS_IDLE */

/*
 * Compensate for the CPU cycles that pass while the SysTick is stopped (low
 * power functionality only.
 */
#if configUSE_TICKLESS_IDLE == 1
	static unsigned long ulStoppedTimerCompensation = 0;
#endif /* configUSE_TICKLESS_IDLE */

/*
 * Used by the portASSERT_IF_INTERRUPT_PRIORITY_INVALID() macro to ensure 
 * FreeRTOS API functions are not called from interrupts that have been assigned
 * a priority above configMAX_SYSCALL_INTERRUPT_PRIORITY.
 */
#if ( configASSERT_DEFINED == 1 )
	 static unsigned char ucMaxSysCallPriority = 0;
	 static const volatile unsigned char * const pcInterruptPriorityRegisters = ( unsigned char * ) portNVIC_IP_REGISTERS_OFFSET_16;
#endif /* configASSERT_DEFINED */

/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
{
	/* Simulate the stack frame as it would be created by a context switch
	interrupt. */
	pxTopOfStack--; /* Offset added to account for the way the MCU uses the stack on entry/exit of interrupts. */
	*pxTopOfStack = portINITIAL_XPSR;	/* xPSR */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) pxCode;	/* PC */
	pxTopOfStack--;
	*pxTopOfStack = 0;	/* LR */
	pxTopOfStack -= 5;	/* R12, R3, R2 and R1. */
	*pxTopOfStack = ( portSTACK_TYPE ) pvParameters;	/* R0 */
	pxTopOfStack -= 8;	/* R11, R10, R9, R8, R7, R6, R5 and R4. */

	return pxTopOfStack;
}
/*-----------------------------------------------------------*/

__asm void vPortSVCHandler( void )
{
	PRESERVE8

	ldr	r3, =pxCurrentTCB	/* Restore the context. */
	ldr r1, [r3]			/* Use pxCurrentTCBConst to get the pxCurrentTCB address. */
	ldr r0, [r1]			/* The first item in pxCurrentTCB is the task top of stack. */
	ldmia r0!, {r4-r11}		/* Pop the registers that are not automatically saved on exception entry and the critical nesting count. */
	msr psp, r0				/* Restore the task stack pointer. */
	mov r0, #0
	msr	basepri, r0
	orr r14, #0xd
	bx r14
}
/*-----------------------------------------------------------*/

__asm void prvStartFirstTask( void )
{
	PRESERVE8

	/* Use the NVIC offset register to locate the stack. */
	ldr r0, =0xE000ED08
	ldr r0, [r0]
	ldr r0, [r0]
	/* Set the msp back to the start of the stack. */
	msr msp, r0
	/* Globally enable interrupts. */
	cpsie i
	/* Call SVC to start the first task. */
	svc 0
	nop
}
/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
portBASE_TYPE xPortStartScheduler( void )
{
	#if( configASSERT_DEFINED == 1 )
	{
		volatile unsigned long ulOriginalPriority;
		volatile char * const pcFirstUserPriorityRegister = ( char * ) ( portNVIC_IP_REGISTERS_OFFSET_16 + portFIRST_USER_INTERRUPT_NUMBER );

		/* Determine the maximum priority from which ISR safe FreeRTOS API
		functions can be called.  ISR safe functions are those that end in
		"FromISR".  FreeRTOS maintains separate thread and ISR API functions to
		ensure interrupt entry is as fast and simple as possible.

		Save the interrupt priority value that is about to be clobbered. */
		ulOriginalPriority = *pcFirstUserPriorityRegister;

		/* Write the configMAX_SYSCALL_INTERRUPT_PRIORITY value to an interrupt
		priority register. */
		*pcFirstUserPriorityRegister = configMAX_SYSCALL_INTERRUPT_PRIORITY;

		/* Read back the written priority to obtain its value as seen by the
		hardware, which will only implement a subset of the priority bits. */
		ucMaxSysCallPriority = *pcFirstUserPriorityRegister;

		/* Restore the clobbered interrupt priority register to its original
		value. */
		*pcFirstUserPriorityRegister = ulOriginalPriority;
	}
	#endif /* conifgASSERT_DEFINED */

	/* Make PendSV and SysTick the lowest priority interrupts. */
	portNVIC_SYSPRI2_REG |= portNVIC_PENDSV_PRI;
	portNVIC_SYSPRI2_REG |= portNVIC_SYSTICK_PRI;

	/* Start the timer that generates the tick ISR.  Interrupts are disabled
	here already. */
	vPortSetupTimerInterrupt();

	/* Initialise the critical nesting count ready for the first task. */
	uxCriticalNesting = 0;

	/* Start the first task. */
	prvStartFirstTask();

	/* Should not get here! */
	return 0;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
	/* It is unlikely that the CM3 port will require this function as there
	is nothing to return to.  */
}
/*-----------------------------------------------------------*/

void vPortYield( void )
{
	/* Set a PendSV to request a context switch. */
	portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;

	/* Barriers are normally not required but do ensure the code is completely
	within the specified behaviour for the architecture. */
	__dsb( portSY_FULL_READ_WRITE );
	__isb( portSY_FULL_READ_WRITE );
}
/*-----------------------------------------------------------*/

void vPortEnterCritical( void )
{
	portDISABLE_INTERRUPTS();
	uxCriticalNesting++;
	__dsb( portSY_FULL_READ_WRITE );
	__isb( portSY_FULL_READ_WRITE );
}
/*-----------------------------------------------------------*/

void vPortExitCritical( void )
{
	uxCriticalNesting--;
	if( uxCriticalNesting == 0 )
	{
		portENABLE_INTERRUPTS();
	}
}
/*-----------------------------------------------------------*/

__asm void xPortPendSVHandler( void )
{
	extern uxCriticalNesting;
	extern pxCurrentTCB;
	extern vTaskSwitchContext;

	PRESERVE8

	mrs r0, psp

	ldr	r3, =pxCurrentTCB		/* Get the location of the current TCB. */
	ldr	r2, [r3]

	stmdb r0!, {r4-r11}			/* Save the remaining registers. */
	str r0, [r2]				/* Save the new top of stack into the first member of the TCB. */

	stmdb sp!, {r3, r14}
	mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY
	msr basepri, r0
	bl vTaskSwitchContext
	mov r0, #0
	msr basepri, r0
	ldmia sp!, {r3, r14}

	ldr r1, [r3]
	ldr r0, [r1]				/* The first item in pxCurrentTCB is the task top of stack. */
	ldmia r0!, {r4-r11}			/* Pop the registers and the critical nesting count. */
	msr psp, r0
	bx r14
	nop
}
/*-----------------------------------------------------------*/

void xPortSysTickHandler( void )
{
	/* The SysTick runs at the lowest interrupt priority, so when this interrupt
	executes all interrupts must be unmasked.  There is therefore no need to
	save and then restore the interrupt mask value as its value is already
	known. */
	( void ) portSET_INTERRUPT_MASK_FROM_ISR();
	{
		/* Increment the RTOS tick. */
		if( xTaskIncrementTick() != pdFALSE )
		{
			/* A context switch is required.  Context switching is performed in
			the PendSV interrupt.  Pend the PendSV interrupt. */
			portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;
		}
	}
	portCLEAR_INTERRUPT_MASK_FROM_ISR( 0 );
}
/*-----------------------------------------------------------*/

#if configUSE_TICKLESS_IDLE == 1

	__weak void vPortSuppressTicksAndSleep( portTickType xExpectedIdleTime )
	{
	unsigned long ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements;
	portTickType xModifiableIdleTime;

		/* Make sure the SysTick reload value does not overflow the counter. */
		if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
		{
			xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
		}

		/* Stop the SysTick momentarily.  The time the SysTick is stopped for
		is accounted for as best it can be, but using the tickless mode will
		inevitably result in some tiny drift of the time maintained by the
		kernel with respect to calendar time. */
		portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT;

		/* Calculate the reload value required to wait xExpectedIdleTime
		tick periods.  -1 is used because this code will execute part way
		through one of the tick periods. */
		ulReloadValue = portNVIC_SYSTICK_CURRENT_VALUE_REG + ( ulTimerCountsForOneTick * ( xExpectedIdleTime - 1UL ) );
		if( ulReloadValue > ulStoppedTimerCompensation )
		{
			ulReloadValue -= ulStoppedTimerCompensation;
		}

		/* Enter a critical section but don't use the taskENTER_CRITICAL()
		method as that will mask interrupts that should exit sleep mode. */
		__disable_irq();

		/* If a context switch is pending or a task is waiting for the scheduler
		to be unsuspended then abandon the low power entry. */
		if( eTaskConfirmSleepModeStatus() == eAbortSleep )
		{
			/* Restart SysTick. */
			portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;

			/* Re-enable interrupts - see comments above __disable_irq() call
			above. */
			__enable_irq();
		}
		else
		{
			/* Set the new reload value. */
			portNVIC_SYSTICK_LOAD_REG = ulReloadValue;

			/* Clear the SysTick count flag and set the count value back to
			zero. */
			portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;

			/* Restart SysTick. */
			portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;

			/* Sleep until something happens.  configPRE_SLEEP_PROCESSING() can
			set its parameter to 0 to indicate that its implementation contains
			its own wait for interrupt or wait for event instruction, and so wfi
			should not be executed again.  However, the original expected idle
			time variable must remain unmodified, so a copy is taken. */
			xModifiableIdleTime = xExpectedIdleTime;
			configPRE_SLEEP_PROCESSING( xModifiableIdleTime );
			if( xModifiableIdleTime > 0 )
			{
				__dsb( portSY_FULL_READ_WRITE );
				__wfi();
				__isb( portSY_FULL_READ_WRITE );
			}
			configPOST_SLEEP_PROCESSING( xExpectedIdleTime );

			/* Stop SysTick.  Again, the time the SysTick is stopped for is
			accounted for as best it can be, but using the tickless mode will
			inevitably result in some tiny drift of the time maintained by the
			kernel with respect to calendar time. */
			portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT;

			/* Re-enable interrupts - see comments above __disable_irq() call
			above. */
			__enable_irq();

			if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
			{
				/* The tick interrupt has already executed, and the SysTick
				count reloaded with ulReloadValue.  Reset the
				portNVIC_SYSTICK_LOAD_REG with whatever remains of this tick
				period. */
				portNVIC_SYSTICK_LOAD_REG = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );

				/* The tick interrupt handler will already have pended the tick
				processing in the kernel.  As the pending tick will be
				processed as soon as this function exits, the tick value
				maintained by the tick is stepped forward by one less than the
				time spent waiting. */
				ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
			}
			else
			{
				/* Something other than the tick interrupt ended the sleep.
				Work out how long the sleep lasted rounded to complete tick
				periods (not the ulReload value which accounted for part
				ticks). */
				ulCompletedSysTickDecrements = ( xExpectedIdleTime * ulTimerCountsForOneTick ) - portNVIC_SYSTICK_CURRENT_VALUE_REG;

				/* How many complete tick periods passed while the processor
				was waiting? */
				ulCompleteTickPeriods = ulCompletedSysTickDecrements / ulTimerCountsForOneTick;

				/* The reload value is set to whatever fraction of a single tick
				period remains. */
				portNVIC_SYSTICK_LOAD_REG = ( ( ulCompleteTickPeriods + 1 ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
			}

			/* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG
			again, then set portNVIC_SYSTICK_LOAD_REG back to its standard
			value. */
			portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
			portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;

			vTaskStepTick( ulCompleteTickPeriods );

			/* The counter must start by the time the reload value is reset. */
			configASSERT( portNVIC_SYSTICK_CURRENT_VALUE_REG );
			portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
		}
	}

#endif /* #if configUSE_TICKLESS_IDLE */

/*-----------------------------------------------------------*/

/*
 * Setup the SysTick timer to generate the tick interrupts at the required
 * frequency.
 */
#if configOVERRIDE_DEFAULT_TICK_CONFIGURATION == 0

	void vPortSetupTimerInterrupt( void )
	{
		/* Calculate the constants required to configure the tick interrupt. */
		#if configUSE_TICKLESS_IDLE == 1
		{
			ulTimerCountsForOneTick = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ );
			xMaximumPossibleSuppressedTicks = portMAX_24_BIT_NUMBER / ulTimerCountsForOneTick;
			ulStoppedTimerCompensation = portMISSED_COUNTS_FACTOR / ( configCPU_CLOCK_HZ / configSYSTICK_CLOCK_HZ );
		}
		#endif /* configUSE_TICKLESS_IDLE */

		/* Configure SysTick to interrupt at the requested rate. */
		portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;;
		portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;
	}

#endif /* configOVERRIDE_DEFAULT_TICK_CONFIGURATION */
/*-----------------------------------------------------------*/

__asm unsigned long ulPortSetInterruptMask( void )
{
	PRESERVE8

	mrs r0, basepri
	mov r1, #configMAX_SYSCALL_INTERRUPT_PRIORITY
	msr basepri, r1
	bx r14
}
/*-----------------------------------------------------------*/

__asm void vPortClearInterruptMask( unsigned long ulNewMask )
{
	PRESERVE8

	msr basepri, r0
	bx r14
}
/*-----------------------------------------------------------*/

__asm unsigned long vPortGetIPSR( void )
{
	PRESERVE8
	
	mrs r0, ipsr
	bx r14
}
/*-----------------------------------------------------------*/

#if( configASSERT_DEFINED == 1 )

	void vPortValidateInterruptPriority( void )
	{
	unsigned long ulCurrentInterrupt;
	unsigned char ucCurrentPriority;

		/* Obtain the number of the currently executing interrupt. */
		ulCurrentInterrupt = vPortGetIPSR();

		/* Is the interrupt number a user defined interrupt? */
		if( ulCurrentInterrupt >= portFIRST_USER_INTERRUPT_NUMBER )
		{
			/* Look up the interrupt's priority. */
			ucCurrentPriority = pcInterruptPriorityRegisters[ ulCurrentInterrupt ];

			/* The following assertion will fail if a service routine (ISR) for 
			an interrupt that has been assigned a priority above
			configMAX_SYSCALL_INTERRUPT_PRIORITY calls an ISR safe FreeRTOS API
			function.  ISR safe FreeRTOS API functions must *only* be called 
			from interrupts that have been assigned a priority at or below
			configMAX_SYSCALL_INTERRUPT_PRIORITY.
			
			Numerically low interrupt priority numbers represent logically high
			interrupt priorities, therefore the priority of the interrupt must 
			be set to a value equal to or numerically *higher* than 
			configMAX_SYSCALL_INTERRUPT_PRIORITY.
			
			Interrupts that	use the FreeRTOS API must not be left at their
			default priority of	zero as that is the highest possible priority,
			which is guaranteed to be above configMAX_SYSCALL_INTERRUPT_PRIORITY, 
			and	therefore also guaranteed to be invalid.  
			
			FreeRTOS maintains separate thread and ISR API functions to ensure 
			interrupt entry is as fast and simple as possible.
			
			The following links provide detailed information:
			http://www.freertos.org/RTOS-Cortex-M3-M4.html
			http://www.freertos.org/FAQHelp.html */
			configASSERT( ucCurrentPriority >= ucMaxSysCallPriority );
		}

		/* Priority grouping:  The interrupt controller (NVIC) allows the bits 
		that define each interrupt's priority to be split between bits that 
		define the interrupt's pre-emption priority bits and bits that define
		the interrupt's sub-priority.  For simplicity all bits must be defined 
		to be pre-emption priority bits.  The following assertion will fail if
		this is not the case (if some bits represent a sub-priority).  
		
		If CMSIS libraries are being used then the correct setting can be 
		achieved by calling	NVIC_SetPriorityGrouping( 0 ); before starting the 
		scheduler. */
		configASSERT( ( portAIRCR_REG & portPRIORITY_GROUP_MASK ) == 0 );
	}

#endif /* configASSERT_DEFINED */