/*
 * FreeRTOS Kernel V10.3.1
 * Copyright (C) 2020 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * http://www.FreeRTOS.org
 * http://aws.amazon.com/freertos
 *
 * 1 tab == 4 spaces!
 */

/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the ARM CM3 port.
 *----------------------------------------------------------*/

/* Defining MPU_WRAPPERS_INCLUDED_FROM_API_FILE prevents task.h from redefining
 * all the API functions to use the MPU wrappers.  That should only be done when
 * task.h is included from an application file. */
#define MPU_WRAPPERS_INCLUDED_FROM_API_FILE

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

#undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE

#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	( 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	( 0 )
#endif

/* Constants required to access and manipulate the NVIC. */
#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 ) )
#define portNVIC_SYSPRI1_REG					( * ( ( volatile uint32_t * ) 0xe000ed1c ) )
#define portNVIC_SYS_CTRL_STATE_REG				( * ( ( volatile uint32_t * ) 0xe000ed24 ) )
#define portNVIC_MEM_FAULT_ENABLE				( 1UL << 16UL )

/* Constants required to access and manipulate the MPU. */
#define portMPU_TYPE_REG						( * ( ( volatile uint32_t * ) 0xe000ed90 ) )
#define portMPU_REGION_BASE_ADDRESS_REG			( * ( ( volatile uint32_t * ) 0xe000ed9C ) )
#define portMPU_REGION_ATTRIBUTE_REG			( * ( ( volatile uint32_t * ) 0xe000edA0 ) )
#define portMPU_CTRL_REG						( * ( ( volatile uint32_t * ) 0xe000ed94 ) )
#define portEXPECTED_MPU_TYPE_VALUE				( 8UL << 8UL ) /* 8 regions, unified. */
#define portMPU_ENABLE							( 0x01UL )
#define portMPU_BACKGROUND_ENABLE				( 1UL << 2UL )
#define portPRIVILEGED_EXECUTION_START_ADDRESS	( 0UL )
#define portMPU_REGION_VALID					( 0x10UL )
#define portMPU_REGION_ENABLE					( 0x01UL )
#define portPERIPHERALS_START_ADDRESS			0x40000000UL
#define portPERIPHERALS_END_ADDRESS				0x5FFFFFFFUL

/* Constants required to access and manipulate the SysTick. */
#define portNVIC_SYSTICK_INT					( 0x00000002UL )
#define portNVIC_SYSTICK_ENABLE					( 0x00000001UL )
#define portNVIC_PENDSV_PRI						( ( ( uint32_t ) configKERNEL_INTERRUPT_PRIORITY ) << 16UL )
#define portNVIC_SYSTICK_PRI					( ( ( uint32_t ) configKERNEL_INTERRUPT_PRIORITY ) << 24UL )
#define portNVIC_SVC_PRI						( ( ( uint32_t ) configMAX_SYSCALL_INTERRUPT_PRIORITY - 1UL ) << 24UL )

/* Constants required to set up the initial stack. */
#define portINITIAL_XPSR						( 0x01000000 )
#define portINITIAL_CONTROL_IF_UNPRIVILEGED		( 0x03 )
#define portINITIAL_CONTROL_IF_PRIVILEGED		( 0x02 )

/* 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 )

/* Offsets in the stack to the parameters when inside the SVC handler. */
#define portOFFSET_TO_PC						( 6 )

/* For strict compliance with the Cortex-M spec the task start address should
 * have bit-0 clear, as it is loaded into the PC on exit from an ISR. */
#define portSTART_ADDRESS_MASK					( ( StackType_t ) 0xfffffffeUL )
/*-----------------------------------------------------------*/

/*
 * Configure a number of standard MPU regions that are used by all tasks.
 */
static void prvSetupMPU( void ) PRIVILEGED_FUNCTION;

/*
 * Return the smallest MPU region size that a given number of bytes will fit
 * into.  The region size is returned as the value that should be programmed
 * into the region attribute register for that region.
 */
static uint32_t prvGetMPURegionSizeSetting( uint32_t ulActualSizeInBytes ) PRIVILEGED_FUNCTION;

/*
 * 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 );

/*
 * Standard FreeRTOS exception handlers.
 */
void xPortPendSVHandler( void ) __attribute__ (( naked )) PRIVILEGED_FUNCTION;
void xPortSysTickHandler( void )  __attribute__ ((optimize("3"))) PRIVILEGED_FUNCTION;
void vPortSVCHandler( void ) __attribute__ (( naked )) PRIVILEGED_FUNCTION;

/*
 * Starts the scheduler by restoring the context of the first task to run.
 */
static void prvRestoreContextOfFirstTask( void ) __attribute__(( naked )) PRIVILEGED_FUNCTION;

/*
 * C portion of the SVC handler.  The SVC handler is split between an asm entry
 * and a C wrapper for simplicity of coding and maintenance.
 */
static void prvSVCHandler( uint32_t *pulRegisters ) __attribute__(( noinline )) PRIVILEGED_FUNCTION;

/**
 * @brief Checks whether or not the processor is privileged.
 *
 * @return 1 if the processor is already privileged, 0 otherwise.
 */
BaseType_t xIsPrivileged( void ) __attribute__ (( naked ));

/**
 * @brief Lowers the privilege level by setting the bit 0 of the CONTROL
 * register.
 *
 * Bit 0 of the CONTROL register defines the privilege level of Thread Mode.
 *  Bit[0] = 0 --> The processor is running privileged
 *  Bit[0] = 1 --> The processor is running unprivileged.
 */
void vResetPrivilege( void ) __attribute__ (( naked ));

/**
 * @brief Calls the port specific code to raise the privilege.
 *
 * @return pdFALSE if privilege was raised, pdTRUE otherwise.
 */
extern BaseType_t xPortRaisePrivilege( void );

/**
 * @brief If xRunningPrivileged is not pdTRUE, calls the port specific
 * code to reset the privilege, otherwise does nothing.
 */
extern void vPortResetPrivilege( BaseType_t xRunningPrivileged );
/*-----------------------------------------------------------*/

/* Each task maintains its own interrupt status in the critical nesting
 * variable.  Note this is not saved as part of the task context as context
 * switches can only occur when uxCriticalNesting is zero. */
static UBaseType_t uxCriticalNesting = 0xaaaaaaaa;

/*
 * 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, BaseType_t xRunPrivileged )
{
	/* 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 = ( ( StackType_t ) pxCode ) & portSTART_ADDRESS_MASK;	/* PC */
	pxTopOfStack--;
	*pxTopOfStack = 0;	/* LR */
	pxTopOfStack -= 5;	/* R12, R3, R2 and R1. */
	*pxTopOfStack = ( StackType_t ) pvParameters;	/* R0 */
	pxTopOfStack -= 9;	/* R11, R10, R9, R8, R7, R6, R5 and R4. */

	if( xRunPrivileged == pdTRUE )
	{
		*pxTopOfStack = portINITIAL_CONTROL_IF_PRIVILEGED;
	}
	else
	{
		*pxTopOfStack = portINITIAL_CONTROL_IF_UNPRIVILEGED;
	}

	return pxTopOfStack;
}
/*-----------------------------------------------------------*/

void vPortSVCHandler( void )
{
	/* Assumes psp was in use. */
	__asm volatile
	(
		#ifndef USE_PROCESS_STACK	/* Code should not be required if a main() is using the process stack. */
			"	tst lr, #4						\n"
			"	ite eq							\n"
			"	mrseq r0, msp					\n"
			"	mrsne r0, psp					\n"
		#else
			"	mrs r0, psp						\n"
		#endif
			"	b %0							\n"
			::"i"(prvSVCHandler):"r0", "memory"
	);
}
/*-----------------------------------------------------------*/

static void prvSVCHandler(	uint32_t *pulParam )
{
uint8_t ucSVCNumber;
uint32_t ulPC;
#if( configENFORCE_SYSTEM_CALLS_FROM_KERNEL_ONLY == 1 )
	#if defined( __ARMCC_VERSION )
		/* Declaration when these variable are defined in code instead of being
		 * exported from linker scripts. */
		extern uint32_t * __syscalls_flash_start__;
		extern uint32_t * __syscalls_flash_end__;
	#else
		/* Declaration when these variable are exported from linker scripts. */
		extern uint32_t __syscalls_flash_start__[];
		extern uint32_t __syscalls_flash_end__[];
	#endif /* #if defined( __ARMCC_VERSION ) */
#endif /* #if( configENFORCE_SYSTEM_CALLS_FROM_KERNEL_ONLY == 1 ) */

	/* The stack contains: r0, r1, r2, r3, r12, LR, PC and xPSR.  The first
	 * argument (r0) is pulParam[ 0 ]. */
	ulPC = pulParam[ portOFFSET_TO_PC ];
	ucSVCNumber = ( ( uint8_t * ) ulPC )[ -2 ];

	switch( ucSVCNumber )
	{
		case portSVC_START_SCHEDULER	:	portNVIC_SYSPRI1_REG |= portNVIC_SVC_PRI;
											prvRestoreContextOfFirstTask();
											break;

		case portSVC_YIELD				:	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. */
											__asm volatile( "dsb" ::: "memory" );
											__asm volatile( "isb" );

											break;


	#if( configENFORCE_SYSTEM_CALLS_FROM_KERNEL_ONLY == 1 )
		case portSVC_RAISE_PRIVILEGE	:	/* Only raise the privilege, if the
											 * svc was raised from any of the
											 * system calls. */
											if( ulPC >= ( uint32_t ) __syscalls_flash_start__ &&
												ulPC <= ( uint32_t ) __syscalls_flash_end__ )
											{
												__asm volatile
												(
													"	mrs r1, control		\n" /* Obtain current control value. */
													"	bic r1, #1			\n" /* Set privilege bit. */
													"	msr control, r1		\n" /* Write back new control value. */
													::: "r1", "memory"
												);
											}
											break;
	#else
		case portSVC_RAISE_PRIVILEGE	:	__asm volatile
											(
												"	mrs r1, control		\n" /* Obtain current control value. */
												"	bic r1, #1			\n" /* Set privilege bit. */
												"	msr control, r1		\n" /* Write back new control value. */
												::: "r1", "memory"
											);
											break;
	#endif /* #if( configENFORCE_SYSTEM_CALLS_FROM_KERNEL_ONLY == 1 ) */

		default							:	/* Unknown SVC call. */
											break;
	}
}
/*-----------------------------------------------------------*/

static void prvRestoreContextOfFirstTask( void )
{
	__asm volatile
	(
		"	ldr r0, =0xE000ED08				\n" /* Use the NVIC offset register to locate the stack. */
		"	ldr r0, [r0]					\n"
		"	ldr r0, [r0]					\n"
		"	msr msp, r0						\n" /* Set the msp back to the start of the stack. */
		"	ldr	r3, pxCurrentTCBConst2		\n" /* Restore the context. */
		"	ldr r1, [r3]					\n"
		"	ldr r0, [r1]					\n" /* The first item in the TCB is the task top of stack. */
		"	add r1, r1, #4					\n" /* Move onto the second item in the TCB... */
		"									\n"
		"	dmb								\n" /* Complete outstanding transfers before disabling MPU. */
		"	ldr r2, =0xe000ed94				\n" /* MPU_CTRL register. */
		"	ldr r3, [r2]					\n" /* Read the value of MPU_CTRL. */
		"	bic r3, #1						\n" /* r3 = r3 & ~1 i.e. Clear the bit 0 in r3. */
		"	str r3, [r2]					\n" /* Disable MPU. */
		"									\n"
		"	ldr r2, =0xe000ed9c				\n" /* Region Base Address register. */
		"	ldmia r1!, {r4-r11}				\n" /* Read 4 sets of MPU registers. */
		"	stmia r2!, {r4-r11}				\n" /* Write 4 sets of MPU registers. */
		"									\n"
		"	ldr r2, =0xe000ed94				\n" /* MPU_CTRL register. */
		"	ldr r3, [r2]					\n" /* Read the value of MPU_CTRL. */
		"	orr r3, #1						\n" /* r3 = r3 | 1 i.e. Set the bit 0 in r3. */
		"	str r3, [r2]					\n" /* Enable MPU. */
		"	dsb								\n" /* Force memory writes before continuing. */
		"									\n"
		"	ldmia r0!, {r3, r4-r11}			\n" /* Pop the registers that are not automatically saved on exception entry. */
		"	msr control, r3					\n"
		"	msr psp, r0						\n" /* Restore the task stack pointer. */
		"	mov r0, #0						\n"
		"	msr	basepri, r0					\n"
		"	ldr r14, =0xfffffffd			\n" /* Load exec return code. */
		"	bx r14							\n"
		"									\n"
		"	.align 4						\n"
		"pxCurrentTCBConst2: .word pxCurrentTCB	\n"
	);
}
/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
BaseType_t xPortStartScheduler( void )
{
	/* configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to 0.  See
	 * http://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html */
	configASSERT( ( configMAX_SYSCALL_INTERRUPT_PRIORITY ) );

	#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;
		}

		#ifdef __NVIC_PRIO_BITS
		{
			/* Check the CMSIS configuration that defines the number of
			 * priority bits matches the number of priority bits actually queried
			 * from the hardware. */
			configASSERT( ( portMAX_PRIGROUP_BITS - ulMaxPRIGROUPValue ) == __NVIC_PRIO_BITS );
		}
		#endif

		#ifdef configPRIO_BITS
		{
			/* Check the FreeRTOS configuration that defines the number of
			 * priority bits matches the number of priority bits actually queried
			 * from the hardware. */
			configASSERT( ( portMAX_PRIGROUP_BITS - ulMaxPRIGROUPValue ) == configPRIO_BITS );
		}
		#endif

		/* 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 same priority as the kernel, and the SVC
	 * handler higher priority so it can be used to exit a critical section (where
	 * lower priorities are masked). */
	portNVIC_SYSPRI2_REG |= portNVIC_PENDSV_PRI;
	portNVIC_SYSPRI2_REG |= portNVIC_SYSTICK_PRI;

	/* Configure the regions in the MPU that are common to all tasks. */
	prvSetupMPU();

	/* 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. */
	__asm volatile(
					" ldr r0, =0xE000ED08 	\n" /* Use the NVIC offset register to locate the stack. */
					" ldr r0, [r0] 			\n"
					" ldr r0, [r0] 			\n"
					" msr msp, r0			\n" /* Set the msp back to the start of the stack. */
					" cpsie i				\n" /* Globally enable interrupts. */
					" cpsie f				\n"
					" dsb					\n"
					" isb					\n"
					" svc %0				\n" /* System call to start first task. */
					" nop					\n"
					:: "i" (portSVC_START_SCHEDULER) : "memory" );

	/* 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 )
{
BaseType_t xRunningPrivileged = xPortRaisePrivilege();

	portDISABLE_INTERRUPTS();
	uxCriticalNesting++;

	vPortResetPrivilege( xRunningPrivileged );
}
/*-----------------------------------------------------------*/

void vPortExitCritical( void )
{
BaseType_t xRunningPrivileged = xPortRaisePrivilege();

	configASSERT( uxCriticalNesting );
	uxCriticalNesting--;
	if( uxCriticalNesting == 0 )
	{
		portENABLE_INTERRUPTS();
	}
	vPortResetPrivilege( xRunningPrivileged );
}
/*-----------------------------------------------------------*/

void xPortPendSVHandler( void )
{
	/* This is a naked function. */

	__asm volatile
	(
		"	mrs r0, psp							\n"
		"										\n"
		"	ldr	r3, pxCurrentTCBConst			\n" /* Get the location of the current TCB. */
		"	ldr	r2, [r3]						\n"
		"										\n"
		"	mrs r1, control						\n"
		"	stmdb r0!, {r1, r4-r11}				\n" /* Save the remaining registers. */
		"	str r0, [r2]						\n" /* Save the new top of stack into the first member of the TCB. */
		"										\n"
		"	stmdb sp!, {r3, r14}				\n"
		"	mov r0, %0							\n"
		"	msr basepri, r0						\n"
		"	dsb									\n"
		"	isb									\n"
		"	bl vTaskSwitchContext				\n"
		"	mov r0, #0							\n"
		"	msr basepri, r0						\n"
		"	ldmia sp!, {r3, r14}				\n"
		"										\n"	/* Restore the context. */
		"	ldr r1, [r3]						\n"
		"	ldr r0, [r1]						\n" /* The first item in the TCB is the task top of stack. */
		"	add r1, r1, #4						\n" /* Move onto the second item in the TCB... */
		"										\n"
		"	dmb									\n" /* Complete outstanding transfers before disabling MPU. */
		"	ldr r2, =0xe000ed94					\n" /* MPU_CTRL register. */
		"	ldr r3, [r2]						\n" /* Read the value of MPU_CTRL. */
		"	bic r3, #1							\n" /* r3 = r3 & ~1 i.e. Clear the bit 0 in r3. */
		"	str r3, [r2]						\n" /* Disable MPU. */
		"										\n"
		"	ldr r2, =0xe000ed9c					\n" /* Region Base Address register. */
		"	ldmia r1!, {r4-r11}					\n" /* Read 4 sets of MPU registers. */
		"	stmia r2!, {r4-r11}					\n" /* Write 4 sets of MPU registers. */
		"										\n"
		"	ldr r2, =0xe000ed94					\n" /* MPU_CTRL register. */
		"	ldr r3, [r2]						\n" /* Read the value of MPU_CTRL. */
		"	orr r3, #1							\n" /* r3 = r3 | 1 i.e. Set the bit 0 in r3. */
		"	str r3, [r2]						\n" /* Enable MPU. */
		"	dsb									\n" /* Force memory writes before continuing. */
		"										\n"
		"	ldmia r0!, {r3, r4-r11}				\n" /* Pop the registers that are not automatically saved on exception entry. */
		"	msr control, r3						\n"
		"										\n"
		"	msr psp, r0							\n"
		"	bx r14								\n"
		"										\n"
		"	.align 4							\n"
		"pxCurrentTCBConst: .word pxCurrentTCB	\n"
		::"i"(configMAX_SYSCALL_INTERRUPT_PRIORITY)
	);
}
/*-----------------------------------------------------------*/

void xPortSysTickHandler( void )
{
uint32_t ulDummy;

	ulDummy = portSET_INTERRUPT_MASK_FROM_ISR();
	{
		/* Increment the RTOS tick. */
		if( xTaskIncrementTick() != pdFALSE )
		{
			/* Pend a context switch. */
			portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;
		}
	}
	portCLEAR_INTERRUPT_MASK_FROM_ISR( ulDummy );
}
/*-----------------------------------------------------------*/

/*
 * Setup the systick timer to generate the tick interrupts at the required
 * frequency.
 */
__attribute__(( weak )) void vPortSetupTimerInterrupt( void )
{
	/* Stop and clear the SysTick. */
	portNVIC_SYSTICK_CTRL_REG = 0UL;
	portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;

	/* 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 | portNVIC_SYSTICK_INT | portNVIC_SYSTICK_ENABLE );
}
/*-----------------------------------------------------------*/

static void prvSetupMPU( void )
{
extern uint32_t __privileged_functions_end__[];
extern uint32_t __FLASH_segment_start__[];
extern uint32_t __FLASH_segment_end__[];
extern uint32_t __privileged_data_start__[];
extern uint32_t __privileged_data_end__[];

	/* Check the expected MPU is present. */
	if( portMPU_TYPE_REG == portEXPECTED_MPU_TYPE_VALUE )
	{
		/* First setup the entire flash for unprivileged read only access. */
		portMPU_REGION_BASE_ADDRESS_REG =	( ( uint32_t ) __FLASH_segment_start__ ) | /* Base address. */
											( portMPU_REGION_VALID ) |
											( portUNPRIVILEGED_FLASH_REGION );

		portMPU_REGION_ATTRIBUTE_REG =	( portMPU_REGION_READ_ONLY ) |
										( portMPU_REGION_CACHEABLE_BUFFERABLE ) |
										( prvGetMPURegionSizeSetting( ( uint32_t ) __FLASH_segment_end__ - ( uint32_t ) __FLASH_segment_start__ ) ) |
										( portMPU_REGION_ENABLE );

		/* Setup the first 16K for privileged only access (even though less
		 * than 10K is actually being used).  This is where the kernel code is
		 * placed. */
		portMPU_REGION_BASE_ADDRESS_REG =	( ( uint32_t ) __FLASH_segment_start__ ) | /* Base address. */
											( portMPU_REGION_VALID ) |
											( portPRIVILEGED_FLASH_REGION );

		portMPU_REGION_ATTRIBUTE_REG =	( portMPU_REGION_PRIVILEGED_READ_ONLY ) |
										( portMPU_REGION_CACHEABLE_BUFFERABLE ) |
										( prvGetMPURegionSizeSetting( ( uint32_t ) __privileged_functions_end__ - ( uint32_t ) __FLASH_segment_start__ ) ) |
										( portMPU_REGION_ENABLE );

		/* Setup the privileged data RAM region.  This is where the kernel data
		 * is placed. */
		portMPU_REGION_BASE_ADDRESS_REG =	( ( uint32_t ) __privileged_data_start__ ) | /* Base address. */
											( portMPU_REGION_VALID ) |
											( portPRIVILEGED_RAM_REGION );

		portMPU_REGION_ATTRIBUTE_REG =	( portMPU_REGION_PRIVILEGED_READ_WRITE ) |
										( portMPU_REGION_CACHEABLE_BUFFERABLE ) |
										prvGetMPURegionSizeSetting( ( uint32_t ) __privileged_data_end__ - ( uint32_t ) __privileged_data_start__ ) |
										( portMPU_REGION_ENABLE );

		/* By default allow everything to access the general peripherals.  The
		 * system peripherals and registers are protected. */
		portMPU_REGION_BASE_ADDRESS_REG =	( portPERIPHERALS_START_ADDRESS ) |
											( portMPU_REGION_VALID ) |
											( portGENERAL_PERIPHERALS_REGION );

		portMPU_REGION_ATTRIBUTE_REG =	( portMPU_REGION_READ_WRITE | portMPU_REGION_EXECUTE_NEVER ) |
										( prvGetMPURegionSizeSetting( portPERIPHERALS_END_ADDRESS - portPERIPHERALS_START_ADDRESS ) ) |
										( portMPU_REGION_ENABLE );

		/* Enable the memory fault exception. */
		portNVIC_SYS_CTRL_STATE_REG |= portNVIC_MEM_FAULT_ENABLE;

		/* Enable the MPU with the background region configured. */
		portMPU_CTRL_REG |= ( portMPU_ENABLE | portMPU_BACKGROUND_ENABLE );
	}
}
/*-----------------------------------------------------------*/

static uint32_t prvGetMPURegionSizeSetting( uint32_t ulActualSizeInBytes )
{
uint32_t ulRegionSize, ulReturnValue = 4;

	/* 32 is the smallest region size, 31 is the largest valid value for
	 * ulReturnValue. */
	for( ulRegionSize = 32UL; ulReturnValue < 31UL; ( ulRegionSize <<= 1UL ) )
	{
		if( ulActualSizeInBytes <= ulRegionSize )
		{
			break;
		}
		else
		{
			ulReturnValue++;
		}
	}

	/* Shift the code by one before returning so it can be written directly
	 * into the the correct bit position of the attribute register. */
	return ( ulReturnValue << 1UL );
}
/*-----------------------------------------------------------*/

BaseType_t xIsPrivileged( void ) /* __attribute__ (( naked )) */
{
	__asm volatile
	(
	"	mrs r0, control							\n" /* r0 = CONTROL. */
	"	tst r0, #1								\n" /* Perform r0 & 1 (bitwise AND) and update the conditions flag. */
	"	ite ne									\n"
	"	movne r0, #0							\n" /* CONTROL[0]!=0. Return false to indicate that the processor is not privileged. */
	"	moveq r0, #1							\n" /* CONTROL[0]==0. Return true to indicate that the processor is privileged. */
	"	bx lr									\n" /* Return. */
	"											\n"
	"	.align 4								\n"
	::: "r0", "memory"
	);
}
/*-----------------------------------------------------------*/

void vResetPrivilege( void ) /* __attribute__ (( naked )) */
{
	__asm volatile
	(
	"	mrs r0, control							\n" /* r0 = CONTROL. */
	"	orr r0, #1								\n" /* r0 = r0 | 1. */
	"	msr control, r0							\n" /* CONTROL = r0. */
	"	bx lr									\n" /* Return to the caller. */
	:::"r0", "memory"
	);
}
/*-----------------------------------------------------------*/

void vPortStoreTaskMPUSettings( xMPU_SETTINGS *xMPUSettings, const struct xMEMORY_REGION * const xRegions, StackType_t *pxBottomOfStack, uint32_t ulStackDepth )
{
extern uint32_t __SRAM_segment_start__[];
extern uint32_t __SRAM_segment_end__[];
extern uint32_t __privileged_data_start__[];
extern uint32_t __privileged_data_end__[];
int32_t lIndex;
uint32_t ul;

	if( xRegions == NULL )
	{
		/* No MPU regions are specified so allow access to all RAM. */
		xMPUSettings->xRegion[ 0 ].ulRegionBaseAddress =
				( ( uint32_t ) __SRAM_segment_start__ ) | /* Base address. */
				( portMPU_REGION_VALID ) |
				( portSTACK_REGION );

		xMPUSettings->xRegion[ 0 ].ulRegionAttribute =
				( portMPU_REGION_READ_WRITE ) |
				( portMPU_REGION_CACHEABLE_BUFFERABLE ) |
				( prvGetMPURegionSizeSetting( ( uint32_t ) __SRAM_segment_end__ - ( uint32_t ) __SRAM_segment_start__ ) ) |
				( portMPU_REGION_ENABLE );

		/* Re-instate the privileged only RAM region as xRegion[ 0 ] will have
		 * just removed the privileged only parameters. */
		xMPUSettings->xRegion[ 1 ].ulRegionBaseAddress =
				( ( uint32_t ) __privileged_data_start__ ) | /* Base address. */
				( portMPU_REGION_VALID ) |
				( portSTACK_REGION + 1 );

		xMPUSettings->xRegion[ 1 ].ulRegionAttribute =
				( portMPU_REGION_PRIVILEGED_READ_WRITE ) |
				( portMPU_REGION_CACHEABLE_BUFFERABLE ) |
				prvGetMPURegionSizeSetting( ( uint32_t ) __privileged_data_end__ - ( uint32_t ) __privileged_data_start__ ) |
				( portMPU_REGION_ENABLE );

		/* Invalidate all other regions. */
		for( ul = 2; ul <= portNUM_CONFIGURABLE_REGIONS; ul++ )
		{
			xMPUSettings->xRegion[ ul ].ulRegionBaseAddress = ( portSTACK_REGION + ul ) | portMPU_REGION_VALID;
			xMPUSettings->xRegion[ ul ].ulRegionAttribute = 0UL;
		}
	}
	else
	{
		/* This function is called automatically when the task is created - in
		 * which case the stack region parameters will be valid.  At all other
		 * times the stack parameters will not be valid and it is assumed that the
		 * stack region has already been configured. */
		if( ulStackDepth > 0 )
		{
			/* Define the region that allows access to the stack. */
			xMPUSettings->xRegion[ 0 ].ulRegionBaseAddress =
					( ( uint32_t ) pxBottomOfStack ) |
					( portMPU_REGION_VALID ) |
					( portSTACK_REGION ); /* Region number. */

			xMPUSettings->xRegion[ 0 ].ulRegionAttribute =
					( portMPU_REGION_READ_WRITE ) | /* Read and write. */
					( prvGetMPURegionSizeSetting( ulStackDepth * ( uint32_t ) sizeof( StackType_t ) ) ) |
					( portMPU_REGION_CACHEABLE_BUFFERABLE ) |
					( portMPU_REGION_ENABLE );
		}

		lIndex = 0;

		for( ul = 1; ul <= portNUM_CONFIGURABLE_REGIONS; ul++ )
		{
			if( ( xRegions[ lIndex ] ).ulLengthInBytes > 0UL )
			{
				/* Translate the generic region definition contained in
				 * xRegions into the CM3 specific MPU settings that are then
				 * stored in xMPUSettings. */
				xMPUSettings->xRegion[ ul ].ulRegionBaseAddress =
						( ( uint32_t ) xRegions[ lIndex ].pvBaseAddress ) |
						( portMPU_REGION_VALID ) |
						( portSTACK_REGION + ul ); /* Region number. */

				xMPUSettings->xRegion[ ul ].ulRegionAttribute =
						( prvGetMPURegionSizeSetting( xRegions[ lIndex ].ulLengthInBytes ) ) |
						( xRegions[ lIndex ].ulParameters ) |
						( portMPU_REGION_ENABLE );
			}
			else
			{
				/* Invalidate the region. */
				xMPUSettings->xRegion[ ul ].ulRegionBaseAddress = ( portSTACK_REGION + ul ) | portMPU_REGION_VALID;
				xMPUSettings->xRegion[ ul ].ulRegionAttribute = 0UL;
			}

			lIndex++;
		}
	}
}
/*-----------------------------------------------------------*/

#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 ) :: "memory" );

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