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    the terms of the GNU General Public License (version 2) as published by the
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    ***************************************************************************
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    ***************************************************************************

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    link: http://www.freertos.org/a00114.html

    ***************************************************************************
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*/

/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the ARM CM4F port.
 *----------------------------------------------------------*/

/* Compiler includes. */
#include <intrinsics.h>

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

#ifndef __ARMVFP__
	#error This port can only be used when the project options are configured to enable hardware floating point support.
#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
	/* Ensure the SysTick is clocked at the same frequency as the core. */
	#define portNVIC_SYSTICK_CLK_BIT	( 1UL << 2UL )
#else
	/* The way the SysTick is clocked is not modified in case it is not the same
	as the core. */
	#define portNVIC_SYSTICK_CLK_BIT	( 0 )
#endif

/* Constants required to manipulate the core.  Registers first... */
#define portNVIC_SYSTICK_CTRL_REG			( * ( ( volatile uint32_t * ) 0xe000e010 ) )
#define portNVIC_SYSTICK_LOAD_REG			( * ( ( volatile uint32_t * ) 0xe000e014 ) )
#define portNVIC_SYSTICK_CURRENT_VALUE_REG	( * ( ( volatile uint32_t * ) 0xe000e018 ) )
#define portNVIC_SYSPRI2_REG				( * ( ( volatile uint32_t * ) 0xe000ed20 ) )
/* ...then bits in the registers. */
#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					( ( ( uint32_t ) configKERNEL_INTERRUPT_PRIORITY ) << 16UL )
#define portNVIC_SYSTICK_PRI				( ( ( uint32_t ) configKERNEL_INTERRUPT_PRIORITY ) << 24UL )

/* Constants required to check the validity of an interrupt priority. */
#define portFIRST_USER_INTERRUPT_NUMBER		( 16 )
#define portNVIC_IP_REGISTERS_OFFSET_16 	( 0xE000E3F0 )
#define portAIRCR_REG						( * ( ( volatile uint32_t * ) 0xE000ED0C ) )
#define portMAX_8_BIT_VALUE					( ( uint8_t ) 0xff )
#define portTOP_BIT_OF_BYTE					( ( uint8_t ) 0x80 )
#define portMAX_PRIGROUP_BITS				( ( uint8_t ) 7 )
#define portPRIORITY_GROUP_MASK				( 0x07UL << 8UL )
#define portPRIGROUP_SHIFT					( 8UL )

/* Masks off all bits but the VECTACTIVE bits in the ICSR register. */
#define portVECTACTIVE_MASK					( 0xFFUL )

/* Constants required to manipulate the VFP. */
#define portFPCCR							( ( volatile uint32_t * ) 0xe000ef34 ) /* Floating point context control register. */
#define portASPEN_AND_LSPEN_BITS			( 0x3UL << 30UL )

/* Constants required to set up the initial stack. */
#define portINITIAL_XPSR					( 0x01000000 )
#define portINITIAL_EXEC_RETURN				( 0xfffffffd )

/* 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 UBaseType_t 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 xPortSysTickHandler( void );

/*
 * Start first task is a separate function so it can be tested in isolation.
 */
extern void vPortStartFirstTask( void );

/*
 * Turn the VFP on.
 */
extern void vPortEnableVFP( void );

/*
 * Used to catch tasks that attempt to return from their implementing function.
 */
static void prvTaskExitError( void );

/*-----------------------------------------------------------*/

/*
 * The number of SysTick increments that make up one tick period.
 */
#if configUSE_TICKLESS_IDLE == 1
	static uint32_t 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 uint32_t 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 uint32_t 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 uint8_t ucMaxSysCallPriority = 0;
	 static uint32_t ulMaxPRIGROUPValue = 0;
	 static const volatile uint8_t * const pcInterruptPriorityRegisters = ( const volatile uint8_t * const ) portNVIC_IP_REGISTERS_OFFSET_16;
#endif /* configASSERT_DEFINED */

/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )
{
	/* Simulate the stack frame as it would be created by a context switch
	interrupt. */

	/* Offset added to account for the way the MCU uses the stack on entry/exit
	of interrupts, and to ensure alignment. */
	pxTopOfStack--;

	*pxTopOfStack = portINITIAL_XPSR;	/* xPSR */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) pxCode;	/* PC */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) prvTaskExitError;	/* LR */

	/* Save code space by skipping register initialisation. */
	pxTopOfStack -= 5;	/* R12, R3, R2 and R1. */
	*pxTopOfStack = ( StackType_t ) pvParameters;	/* R0 */

	/* A save method is being used that requires each task to maintain its
	own exec return value. */
	pxTopOfStack--;
	*pxTopOfStack = portINITIAL_EXEC_RETURN;

	pxTopOfStack -= 8;	/* R11, R10, R9, R8, R7, R6, R5 and R4. */

	return pxTopOfStack;
}
/*-----------------------------------------------------------*/

static void prvTaskExitError( void )
{
	/* A function that implements a task must not exit or attempt to return to
	its caller as there is nothing to return to.  If a task wants to exit it
	should instead call vTaskDelete( NULL ).

	Artificially force an assert() to be triggered if configASSERT() is
	defined, then stop here so application writers can catch the error. */
	configASSERT( uxCriticalNesting == ~0UL );
	portDISABLE_INTERRUPTS();
	for( ;; );
}
/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
BaseType_t xPortStartScheduler( void )
{
	#if( configASSERT_DEFINED == 1 )
	{
		volatile uint32_t ulOriginalPriority;
		volatile uint8_t * const pucFirstUserPriorityRegister = ( volatile uint8_t * const ) ( portNVIC_IP_REGISTERS_OFFSET_16 + portFIRST_USER_INTERRUPT_NUMBER );
		volatile uint8_t ucMaxPriorityValue;

		/* 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 = *pucFirstUserPriorityRegister;

		/* Determine the number of priority bits available.  First write to all
		possible bits. */
		*pucFirstUserPriorityRegister = portMAX_8_BIT_VALUE;

		/* Read the value back to see how many bits stuck. */
		ucMaxPriorityValue = *pucFirstUserPriorityRegister;

		/* Use the same mask on the maximum system call priority. */
		ucMaxSysCallPriority = configMAX_SYSCALL_INTERRUPT_PRIORITY & ucMaxPriorityValue;

		/* Calculate the maximum acceptable priority group value for the number
		of bits read back. */
		ulMaxPRIGROUPValue = portMAX_PRIGROUP_BITS;
		while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
		{
			ulMaxPRIGROUPValue--;
			ucMaxPriorityValue <<= ( uint8_t ) 0x01;
		}

		/* Shift the priority group value back to its position within the AIRCR
		register. */
		ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
		ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;

		/* Restore the clobbered interrupt priority register to its original
		value. */
		*pucFirstUserPriorityRegister = 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;

	/* Ensure the VFP is enabled - it should be anyway. */
	vPortEnableVFP();

	/* Lazy save always. */
	*( portFPCCR ) |= portASPEN_AND_LSPEN_BITS;

	/* Start the first task. */
	vPortStartFirstTask();

	/* Should not get here! */
	return 0;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
	/* Not implemented in ports where there is nothing to return to.
	Artificially force an assert. */
	configASSERT( uxCriticalNesting == 1000UL );
}
/*-----------------------------------------------------------*/

void vPortEnterCritical( void )
{
	portDISABLE_INTERRUPTS();
	uxCriticalNesting++;

	/* This is not the interrupt safe version of the enter critical function so
	assert() if it is being called from an interrupt context.  Only API
	functions that end in "FromISR" can be used in an interrupt.  Only assert if
	the critical nesting count is 1 to protect against recursive calls if the
	assert function also uses a critical section. */
	if( uxCriticalNesting == 1 )
	{
		configASSERT( ( portNVIC_INT_CTRL_REG & portVECTACTIVE_MASK ) == 0 );
	}
}
/*-----------------------------------------------------------*/

void vPortExitCritical( void )
{
	configASSERT( uxCriticalNesting );
	uxCriticalNesting--;
	if( uxCriticalNesting == 0 )
	{
		portENABLE_INTERRUPTS();
	}
}
/*-----------------------------------------------------------*/

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. */
	portDISABLE_INTERRUPTS();
	{
		/* 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;
		}
	}
	portENABLE_INTERRUPTS();
}
/*-----------------------------------------------------------*/

#if configUSE_TICKLESS_IDLE == 1

	__weak void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
	{
	uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements, ulSysTickCTRL;
	TickType_t 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_ENABLE_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_interrupt();

		/* 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 from whatever is left in the count register to complete
			this tick period. */
			portNVIC_SYSTICK_LOAD_REG = portNVIC_SYSTICK_CURRENT_VALUE_REG;

			/* Restart SysTick. */
			portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;

			/* Reset the reload register to the value required for normal tick
			periods. */
			portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;

			/* Re-enable interrupts - see comments above __disable_interrupt()
			call above. */
			__enable_interrupt();
		}
		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_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();
				__WFI();
				__ISB();
			}
			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. */
			ulSysTickCTRL = portNVIC_SYSTICK_CTRL_REG;
			portNVIC_SYSTICK_CTRL_REG = ( ulSysTickCTRL & ~portNVIC_SYSTICK_ENABLE_BIT );

			/* Re-enable interrupts - see comments above __disable_interrupt()
			call above. */
			__enable_interrupt();

			if( ( ulSysTickCTRL & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
			{
				uint32_t ulCalculatedLoadValue;

				/* 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. */
				ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );

				/* Don't allow a tiny value, or values that have somehow
				underflowed because the post sleep hook did something
				that took too long. */
				if( ( ulCalculatedLoadValue < ulStoppedTimerCompensation ) || ( ulCalculatedLoadValue > ulTimerCountsForOneTick ) )
				{
					ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL );
				}

				portNVIC_SYSTICK_LOAD_REG = ulCalculatedLoadValue;

				/* 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 + 1UL ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
			}

			/* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG
			again, then set portNVIC_SYSTICK_LOAD_REG back to its standard
			value.  The critical section is used to ensure the tick interrupt
			can only execute once in the case that the reload register is near
			zero. */
			portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
			portENTER_CRITICAL();
			{
				portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
				vTaskStepTick( ulCompleteTickPeriods );
				portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
			}
			portEXIT_CRITICAL();
		}
	}

#endif /* #if configUSE_TICKLESS_IDLE */
/*-----------------------------------------------------------*/

/*
 * Setup the systick timer to generate the tick interrupts at the required
 * frequency.
 */
__weak 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 );
}
/*-----------------------------------------------------------*/

#if( configASSERT_DEFINED == 1 )

	void vPortValidateInterruptPriority( void )
	{
	uint32_t ulCurrentInterrupt;
	uint8_t ucCurrentPriority;

		/* Obtain the number of the currently executing interrupt. */
		__asm volatile( "mrs %0, ipsr" : "=r"( ulCurrentInterrupt ) );

		/* 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 the application only uses CMSIS libraries for interrupt
		configuration then the correct setting can be achieved on all Cortex-M
		devices by calling NVIC_SetPriorityGrouping( 0 ); before starting the
		scheduler.  Note however that some vendor specific peripheral libraries
		assume a non-zero priority group setting, in which cases using a value
		of zero will result in unpredicable behaviour. */
		configASSERT( ( portAIRCR_REG & portPRIORITY_GROUP_MASK ) <= ulMaxPRIGROUPValue );
	}

#endif /* configASSERT_DEFINED */