portable/GCC/ARM_CM4_MPU/port.c

/*
 * 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"

#ifndef __VFP_FP__
	#error This port can only be used when the project options are configured to enable hardware floating point support.
#endif

#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 manipulate the VFP. */
#define portFPCCR								( ( volatile uint32_t * ) 0xe000ef34UL ) /* Floating point context control register. */
#define portASPEN_AND_LSPEN_BITS				( 0x3UL << 30UL )

/* Constants required to set up the initial stack. */
#define portINITIAL_XPSR						( 0x01000000UL )
#define portINITIAL_EXC_RETURN					( 0xfffffffdUL )
#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 ) 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;

/*
 * Function to enable the VFP.
 */
 static void vPortEnableVFP( void ) __attribute__ (( naked ));

/**
 * @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 */

	/* A save method is being used that requires each task to maintain its
	own exec return value. */
	pxTopOfStack--;
	*pxTopOfStack = portINITIAL_EXC_RETURN;

	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 from TCB. */
		"	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-r11, r14}		\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"
		"	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;

	/* Ensure the VFP is enabled - it should be anyway. */
	vPortEnableVFP();

	/* Lazy save always. */
	*( portFPCCR ) |= portASPEN_AND_LSPEN_BITS;

	/* Start the first task.  This also clears the bit that indicates the FPU is
	in use in case the FPU was used before the scheduler was started - which
	would otherwise result in the unnecessary leaving of space in the SVC stack
	for lazy saving of FPU registers. */
	__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. */
					" mov r0, #0			\n" /* Clear the bit that indicates the FPU is in use, see comment above. */
					" msr control, r0		\n"
					" 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"
		"	isb									\n"
		"										\n"
		"	ldr	r3, pxCurrentTCBConst			\n" /* Get the location of the current TCB. */
		"	ldr	r2, [r3]						\n"
		"										\n"
		"	tst r14, #0x10						\n" /* Is the task using the FPU context?  If so, push high vfp registers. */
		"	it eq								\n"
		"	vstmdbeq r0!, {s16-s31}				\n"
		"										\n"
		"	mrs r1, control						\n"
		"	stmdb r0!, {r1, r4-r11, r14}		\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!, {r0, r3}					\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!, {r0, r3}					\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 from TCB. */
		"	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-r11, r14}			\n" /* Pop the registers that are not automatically saved on exception entry. */
		"	msr control, r3						\n"
		"										\n"
		"	tst r14, #0x10						\n" /* Is the task using the FPU context?  If so, pop the high vfp registers too. */
		"	it eq								\n"
		"	vldmiaeq r0!, {s16-s31}				\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 );
}
/*-----------------------------------------------------------*/

/* This is a naked function. */
static void vPortEnableVFP( void )
{
	__asm volatile
	(
		"	ldr.w r0, =0xE000ED88		\n" /* The FPU enable bits are in the CPACR. */
		"	ldr r1, [r0]				\n"
		"								\n"
		"	orr r1, r1, #( 0xf << 20 )	\n" /* Enable CP10 and CP11 coprocessors, then save back. */
		"	str r1, [r0]				\n"
		"	bx r14						"
	);
}
/*-----------------------------------------------------------*/

static void prvSetupMPU( void )
{
#if defined( __ARMCC_VERSION )
	/* Declaration when these variable are defined in code instead of being
	 * exported from linker scripts. */
	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__;
#else
	/* Declaration when these variable are exported from linker scripts. */
	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__[];
#endif
	/* 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 nK 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 )
{
#if defined( __ARMCC_VERSION )
	/* Declaration when these variable are defined in code instead of being
	 * exported from linker scripts. */
	extern uint32_t * __SRAM_segment_start__;
	extern uint32_t * __SRAM_segment_end__;
	extern uint32_t * __privileged_data_start__;
	extern uint32_t * __privileged_data_end__;
#else
	/* Declaration when these variable are exported from linker scripts. */
	extern uint32_t __SRAM_segment_start__[];
	extern uint32_t __SRAM_segment_end__[];
	extern uint32_t __privileged_data_start__[];
	extern uint32_t __privileged_data_end__[];
#endif

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