/*
 * FreeRTOS Kernel <DEVELOPMENT BRANCH>
 * Copyright (C) 2021 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * SPDX-License-Identifier: MIT
 *
 * 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.
 *
 * https://www.FreeRTOS.org
 * https://github.com/FreeRTOS
 *
 */

/*-----------------------------------------------------------
* Implementation of functions defined in portable.h for the ARM CM4F MPU port.
*----------------------------------------------------------*/

/* IAR includes. */
#include <intrinsics.h>

/* 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 __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

#ifndef configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS
    #warning "configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS is not defined. We recommend defining it to 0 in FreeRTOSConfig.h for better security."
    #define configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS    1
#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_SHPR3_REG                        ( *( ( volatile uint32_t * ) 0xe000ed20 ) )
#define portNVIC_SHPR2_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               ( configTOTAL_MPU_REGIONS << 8UL )
#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

/* ...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 )

/* Constants used to detect Cortex-M7 r0p0 and r0p1 cores, and ensure
 * that a work around is active for errata 837070. */
#define portCPUID                                 ( *( ( volatile uint32_t * ) 0xE000ed00 ) )
#define portCORTEX_M7_r0p1_ID                     ( 0x410FC271UL )
#define portCORTEX_M7_r0p0_ID                     ( 0x410FC270UL )

#define portMIN_INTERRUPT_PRIORITY                ( 255UL )
#define portNVIC_PENDSV_PRI                       ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 16UL )
#define portNVIC_SYSTICK_PRI                      ( ( ( uint32_t ) portMIN_INTERRUPT_PRIORITY ) << 24UL )
#define portNVIC_SVC_PRI                          ( ( ( uint32_t ) configMAX_SYSCALL_INTERRUPT_PRIORITY - 1UL ) << 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_EXC_RETURN                    ( 0xfffffffd )
#define portINITIAL_CONTROL_IF_UNPRIVILEGED       ( 0x03 )
#define portINITIAL_CONTROL_IF_PRIVILEGED         ( 0x02 )

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

/* 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 )

/* 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 );

/*
 * Exception handlers.
 */
void xPortSysTickHandler( void ) PRIVILEGED_FUNCTION;

/*
 * Start first task is a separate function so it can be tested in isolation.
 */
extern void vPortStartFirstTask( void ) PRIVILEGED_FUNCTION;

/*
 * Turn the VFP on.
 */
extern void vPortEnableVFP( void );

/*
 * The C portion of the SVC handler.
 */
void vPortSVCHandler_C( uint32_t * pulParam );

/*
 * Called from the SVC handler used to start the scheduler.
 */
extern void vPortRestoreContextOfFirstTask( void ) PRIVILEGED_FUNCTION;

/**
 * @brief Enter critical section.
 */
#if ( configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS == 1 )
    void vPortEnterCritical( void ) FREERTOS_SYSTEM_CALL;
#else
    void vPortEnterCritical( void ) PRIVILEGED_FUNCTION;
#endif

/**
 * @brief Exit from critical section.
 */
#if ( configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS == 1 )
    void vPortExitCritical( void ) FREERTOS_SYSTEM_CALL;
#else
    void vPortExitCritical( void ) PRIVILEGED_FUNCTION;
#endif
/*-----------------------------------------------------------*/

/* Each task maintains its own interrupt status in the critical nesting
 * variable. */
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. */

    /* 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 ) & portSTART_ADDRESS_MASK; /* PC */
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) 0;                                   /* 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_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_C( uint32_t * pulParam )
{
    uint8_t ucSVCNumber;
    uint32_t ulPC;

    #if ( configENFORCE_SYSTEM_CALLS_FROM_KERNEL_ONLY == 1 )
        extern uint32_t __syscalls_flash_start__[];
        extern uint32_t __syscalls_flash_end__[];
    #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_SHPR2_REG |= portNVIC_SVC_PRI;
            vPortRestoreContextOfFirstTask();
            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, r1, #1      \n" /* Set privilege bit. */
                            "   msr control, r1     \n" /* Write back new control value. */
                            ::: "r1", "memory"
                        );
                    }

                    break;
            #else /* if ( configENFORCE_SYSTEM_CALLS_FROM_KERNEL_ONLY == 1 ) */
                case portSVC_RAISE_PRIVILEGE:
                    __asm volatile
                    (
                        "   mrs r1, control     \n" /* Obtain current control value. */
                        "   bic r1, 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;
    }
}
/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
BaseType_t xPortStartScheduler( void )
{
    /* Errata 837070 workaround must only be enabled on Cortex-M7 r0p0
     * and r0p1 cores. */
    #if ( configENABLE_ERRATA_837070_WORKAROUND == 1 )
        configASSERT( ( portCPUID == portCORTEX_M7_r0p1_ID ) || ( portCPUID == portCORTEX_M7_r0p0_ID ) );
    #else

        /* When using this port on a Cortex-M7 r0p0 or r0p1 core, define
         * configENABLE_ERRATA_837070_WORKAROUND to 1 in your
         * FreeRTOSConfig.h. */
        configASSERT( portCPUID != portCORTEX_M7_r0p1_ID );
        configASSERT( portCPUID != portCORTEX_M7_r0p0_ID );
    #endif

    #if ( configASSERT_DEFINED == 1 )
    {
        volatile uint8_t ucOriginalPriority;
        volatile uint32_t ulImplementedPrioBits = 0;
        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. */
        ucOriginalPriority = *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;

        /* Check that the maximum system call priority is nonzero after
         * accounting for the number of priority bits supported by the
         * hardware. A priority of 0 is invalid because setting the BASEPRI
         * register to 0 unmasks all interrupts, and interrupts with priority 0
         * cannot be masked using BASEPRI.
         * See https://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html */
        configASSERT( ucMaxSysCallPriority );

        /* Check that the bits not implemented bits in hardware are zero in
         * configMAX_SYSCALL_INTERRUPT_PRIORITY. */
        configASSERT( ( configMAX_SYSCALL_INTERRUPT_PRIORITY & ( ~ucMaxPriorityValue ) ) == 0U );

        /* Calculate the maximum acceptable priority group value for the number
         * of bits read back. */

        while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
        {
            ulImplementedPrioBits++;
            ucMaxPriorityValue <<= ( uint8_t ) 0x01;
        }

        if( ulImplementedPrioBits == 8 )
        {
            /* When the hardware implements 8 priority bits, there is no way for
            * the software to configure PRIGROUP to not have sub-priorities. As
            * a result, the least significant bit is always used for sub-priority
            * and there are 128 preemption priorities and 2 sub-priorities.
            *
            * This may cause some confusion in some cases - for example, if
            * configMAX_SYSCALL_INTERRUPT_PRIORITY is set to 5, both 5 and 4
            * priority interrupts will be masked in Critical Sections as those
            * are at the same preemption priority. This may appear confusing as
            * 4 is higher (numerically lower) priority than
            * configMAX_SYSCALL_INTERRUPT_PRIORITY and therefore, should not
            * have been masked. Instead, if we set configMAX_SYSCALL_INTERRUPT_PRIORITY
            * to 4, this confusion does not happen and the behaviour remains the same.
            *
            * The following assert ensures that the sub-priority bit in the
            * configMAX_SYSCALL_INTERRUPT_PRIORITY is clear to avoid the above mentioned
            * confusion. */
            configASSERT( ( configMAX_SYSCALL_INTERRUPT_PRIORITY & 0x1U ) == 0U );
            ulMaxPRIGROUPValue = 0;
        }
        else
        {
            ulMaxPRIGROUPValue = portMAX_PRIGROUP_BITS - ulImplementedPrioBits;
        }

        /* 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 = ucOriginalPriority;
    }
    #endif /* configASSERT_DEFINED */

    /* Make PendSV and SysTick the lowest priority interrupts. */
    portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
    portNVIC_SHPR3_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. */
    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 )
{
    #if ( configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS == 1 )
        if( portIS_PRIVILEGED() == pdFALSE )
        {
            portRAISE_PRIVILEGE();
            portMEMORY_BARRIER();

            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 );
            }

            portMEMORY_BARRIER();

            portRESET_PRIVILEGE();
            portMEMORY_BARRIER();
        }
        else
        {
            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 );
            }
        }
    #else /* if ( configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS == 1 ) */
        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 );
        }
    #endif /* if ( configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS == 1 ) */
}
/*-----------------------------------------------------------*/

void vPortExitCritical( void )
{
    #if ( configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS == 1 )
        if( portIS_PRIVILEGED() == pdFALSE )
        {
            portRAISE_PRIVILEGE();
            portMEMORY_BARRIER();

            configASSERT( uxCriticalNesting );
            uxCriticalNesting--;

            if( uxCriticalNesting == 0 )
            {
                portENABLE_INTERRUPTS();
            }

            portMEMORY_BARRIER();

            portRESET_PRIVILEGE();
            portMEMORY_BARRIER();
        }
        else
        {
            configASSERT( uxCriticalNesting );
            uxCriticalNesting--;

            if( uxCriticalNesting == 0 )
            {
                portENABLE_INTERRUPTS();
            }
        }
    #else /* if ( configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS == 1 ) */
        configASSERT( uxCriticalNesting );
        uxCriticalNesting--;

        if( uxCriticalNesting == 0 )
        {
            portENABLE_INTERRUPTS();
        }
    #endif /* if ( configALLOW_UNPRIVILEGED_CRITICAL_SECTIONS == 1 ) */
}
/*-----------------------------------------------------------*/

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();
}
/*-----------------------------------------------------------*/

/*
 * Setup the systick timer to generate the tick interrupts at the required
 * frequency.
 */
__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_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );
}
/*-----------------------------------------------------------*/

static void prvSetupMPU( void )
{
    extern uint32_t __privileged_functions_start__[];
    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__[];

    /* The only permitted number of regions are 8 or 16. */
    configASSERT( ( configTOTAL_MPU_REGIONS == 8 ) || ( configTOTAL_MPU_REGIONS == 16 ) );

    /* Ensure that the configTOTAL_MPU_REGIONS is configured correctly. */
    configASSERT( portMPU_TYPE_REG == portEXPECTED_MPU_TYPE_VALUE );

    /* Check the expected MPU is present. */
    if( portMPU_TYPE_REG == portEXPECTED_MPU_TYPE_VALUE )
    {
        /* First setup the unprivileged 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 ) |
                                       ( ( configTEX_S_C_B_FLASH & portMPU_RASR_TEX_S_C_B_MASK ) << portMPU_RASR_TEX_S_C_B_LOCATION ) |
                                       ( prvGetMPURegionSizeSetting( ( uint32_t ) __FLASH_segment_end__ - ( uint32_t ) __FLASH_segment_start__ ) ) |
                                       ( portMPU_REGION_ENABLE );

        /* Setup the privileged flash for privileged only access.  This is where
         * the kernel code is placed. */
        portMPU_REGION_BASE_ADDRESS_REG = ( ( uint32_t ) __privileged_functions_start__ ) | /* Base address. */
                                          ( portMPU_REGION_VALID ) |
                                          ( portPRIVILEGED_FLASH_REGION );

        portMPU_REGION_ATTRIBUTE_REG = ( portMPU_REGION_PRIVILEGED_READ_ONLY ) |
                                       ( ( configTEX_S_C_B_FLASH & portMPU_RASR_TEX_S_C_B_MASK ) << portMPU_RASR_TEX_S_C_B_LOCATION ) |
                                       ( prvGetMPURegionSizeSetting( ( uint32_t ) __privileged_functions_end__ - ( uint32_t ) __privileged_functions_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_EXECUTE_NEVER ) |
                                       ( ( configTEX_S_C_B_SRAM & portMPU_RASR_TEX_S_C_B_MASK ) << portMPU_RASR_TEX_S_C_B_LOCATION ) |
                                       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 );
}
/*-----------------------------------------------------------*/

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 );                     /* Region number. */

        xMPUSettings->xRegion[ 0 ].ulRegionAttribute =
            ( portMPU_REGION_READ_WRITE ) |
            ( portMPU_REGION_EXECUTE_NEVER ) |
            ( ( configTEX_S_C_B_SRAM & portMPU_RASR_TEX_S_C_B_MASK ) << portMPU_RASR_TEX_S_C_B_LOCATION ) |
            ( prvGetMPURegionSizeSetting( ( uint32_t ) __SRAM_segment_end__ - ( uint32_t ) __SRAM_segment_start__ ) ) |
            ( portMPU_REGION_ENABLE );

        /* Invalidate user configurable regions. */
        for( ul = 1UL; ul <= portNUM_CONFIGURABLE_REGIONS; ul++ )
        {
            xMPUSettings->xRegion[ ul ].ulRegionBaseAddress = ( ( ul - 1UL ) | 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 ) |
                ( portMPU_REGION_EXECUTE_NEVER ) |
                ( prvGetMPURegionSizeSetting( ulStackDepth * ( uint32_t ) sizeof( StackType_t ) ) ) |
                ( ( configTEX_S_C_B_SRAM & portMPU_RASR_TEX_S_C_B_MASK ) << portMPU_RASR_TEX_S_C_B_LOCATION ) |
                ( portMPU_REGION_ENABLE );
        }

        lIndex = 0;

        for( ul = 1UL; ul <= portNUM_CONFIGURABLE_REGIONS; ul++ )
        {
            if( ( xRegions[ lIndex ] ).ulLengthInBytes > 0UL )
            {
                /* Translate the generic region definition contained in
                 * xRegions into the CM4 specific MPU settings that are then
                 * stored in xMPUSettings. */
                xMPUSettings->xRegion[ ul ].ulRegionBaseAddress =
                    ( ( uint32_t ) xRegions[ lIndex ].pvBaseAddress ) |
                    ( portMPU_REGION_VALID ) |
                    ( ul - 1UL ); /* Region number. */

                xMPUSettings->xRegion[ ul ].ulRegionAttribute =
                    ( prvGetMPURegionSizeSetting( xRegions[ lIndex ].ulLengthInBytes ) ) |
                    ( xRegions[ lIndex ].ulParameters ) |
                    ( portMPU_REGION_ENABLE );
            }
            else
            {
                /* Invalidate the region. */
                xMPUSettings->xRegion[ ul ].ulRegionBaseAddress = ( ( ul - 1UL ) | 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:
             * https://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html
             * https://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 unpredictable behaviour. */
        configASSERT( ( portAIRCR_REG & portPRIORITY_GROUP_MASK ) <= ulMaxPRIGROUPValue );
    }

#endif /* configASSERT_DEFINED */
/*-----------------------------------------------------------*/