FreeRTOS-Kernel/portable/ARMv8M/non_secure/port.c

/*
 * 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
 *
 */

/* 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"

/* MPU wrappers includes. */
#include "mpu_wrappers.h"

/* Portasm includes. */
#include "portasm.h"

#if ( configENABLE_TRUSTZONE == 1 )
    /* Secure components includes. */
    #include "secure_context.h"
    #include "secure_init.h"
#endif /* configENABLE_TRUSTZONE */

#undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE

/**
 * The FreeRTOS Cortex M33 port can be configured to run on the Secure Side only
 * i.e. the processor boots as secure and never jumps to the non-secure side.
 * The Trust Zone support in the port must be disabled in order to run FreeRTOS
 * on the secure side. The following are the valid configuration seetings:
 *
 * 1. Run FreeRTOS on the Secure Side:
 *    configRUN_FREERTOS_SECURE_ONLY = 1 and configENABLE_TRUSTZONE = 0
 *
 * 2. Run FreeRTOS on the Non-Secure Side with Secure Side function call support:
 *    configRUN_FREERTOS_SECURE_ONLY = 0 and configENABLE_TRUSTZONE = 1
 *
 * 3. Run FreeRTOS on the Non-Secure Side only i.e. no Secure Side function call support:
 *    configRUN_FREERTOS_SECURE_ONLY = 0 and configENABLE_TRUSTZONE = 0
 */
#if ( ( configRUN_FREERTOS_SECURE_ONLY == 1 ) && ( configENABLE_TRUSTZONE == 1 ) )
    #error TrustZone needs to be disabled in order to run FreeRTOS on the Secure Side.
#endif
/*-----------------------------------------------------------*/

/**
 * @brief Constants required to 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_SHPR3_REG                    ( *( ( volatile uint32_t * ) 0xe000ed20 ) )
#define portNVIC_SYSTICK_ENABLE_BIT           ( 1UL << 0UL )
#define portNVIC_SYSTICK_INT_BIT              ( 1UL << 1UL )
#define portNVIC_SYSTICK_CLK_BIT              ( 1UL << 2UL )
#define portNVIC_SYSTICK_COUNT_FLAG_BIT       ( 1UL << 16UL )
#define portNVIC_PEND_SYSTICK_CLEAR_BIT       ( 1UL << 25UL )
#define portNVIC_PEND_SYSTICK_SET_BIT         ( 1UL << 26UL )
#define portMIN_INTERRUPT_PRIORITY            ( 255UL )
#define portNVIC_PENDSV_PRI                   ( portMIN_INTERRUPT_PRIORITY << 16UL )
#define portNVIC_SYSTICK_PRI                  ( portMIN_INTERRUPT_PRIORITY << 24UL )
/*-----------------------------------------------------------*/

/**
 * @brief Constants required to manipulate the SCB.
 */
#define portSCB_SYS_HANDLER_CTRL_STATE_REG    ( *( volatile uint32_t * ) 0xe000ed24 )
#define portSCB_MEM_FAULT_ENABLE_BIT          ( 1UL << 16UL )
/*-----------------------------------------------------------*/

/**
 * @brief Constants required to manipulate the FPU.
 */
#define portCPACR               ( ( volatile uint32_t * ) 0xe000ed88 )              /* Coprocessor Access Control Register. */
#define portCPACR_CP10_VALUE    ( 3UL )
#define portCPACR_CP11_VALUE    portCPACR_CP10_VALUE
#define portCPACR_CP10_POS      ( 20UL )
#define portCPACR_CP11_POS      ( 22UL )

#define portFPCCR               ( ( volatile uint32_t * ) 0xe000ef34 )              /* Floating Point Context Control Register. */
#define portFPCCR_ASPEN_POS     ( 31UL )
#define portFPCCR_ASPEN_MASK    ( 1UL << portFPCCR_ASPEN_POS )
#define portFPCCR_LSPEN_POS     ( 30UL )
#define portFPCCR_LSPEN_MASK    ( 1UL << portFPCCR_LSPEN_POS )
/*-----------------------------------------------------------*/

/**
 * @brief Constants required to manipulate the MPU.
 */
#define portMPU_TYPE_REG                      ( *( ( volatile uint32_t * ) 0xe000ed90 ) )
#define portMPU_CTRL_REG                      ( *( ( volatile uint32_t * ) 0xe000ed94 ) )
#define portMPU_RNR_REG                       ( *( ( volatile uint32_t * ) 0xe000ed98 ) )

#define portMPU_RBAR_REG                      ( *( ( volatile uint32_t * ) 0xe000ed9c ) )
#define portMPU_RLAR_REG                      ( *( ( volatile uint32_t * ) 0xe000eda0 ) )

#define portMPU_RBAR_A1_REG                   ( *( ( volatile uint32_t * ) 0xe000eda4 ) )
#define portMPU_RLAR_A1_REG                   ( *( ( volatile uint32_t * ) 0xe000eda8 ) )

#define portMPU_RBAR_A2_REG                   ( *( ( volatile uint32_t * ) 0xe000edac ) )
#define portMPU_RLAR_A2_REG                   ( *( ( volatile uint32_t * ) 0xe000edb0 ) )

#define portMPU_RBAR_A3_REG                   ( *( ( volatile uint32_t * ) 0xe000edb4 ) )
#define portMPU_RLAR_A3_REG                   ( *( ( volatile uint32_t * ) 0xe000edb8 ) )

#define portMPU_MAIR0_REG                     ( *( ( volatile uint32_t * ) 0xe000edc0 ) )
#define portMPU_MAIR1_REG                     ( *( ( volatile uint32_t * ) 0xe000edc4 ) )

#define portMPU_RBAR_ADDRESS_MASK             ( 0xffffffe0 ) /* Must be 32-byte aligned. */
#define portMPU_RLAR_ADDRESS_MASK             ( 0xffffffe0 ) /* Must be 32-byte aligned. */

#define portMPU_MAIR_ATTR0_POS                ( 0UL )
#define portMPU_MAIR_ATTR0_MASK               ( 0x000000ff )

#define portMPU_MAIR_ATTR1_POS                ( 8UL )
#define portMPU_MAIR_ATTR1_MASK               ( 0x0000ff00 )

#define portMPU_MAIR_ATTR2_POS                ( 16UL )
#define portMPU_MAIR_ATTR2_MASK               ( 0x00ff0000 )

#define portMPU_MAIR_ATTR3_POS                ( 24UL )
#define portMPU_MAIR_ATTR3_MASK               ( 0xff000000 )

#define portMPU_MAIR_ATTR4_POS                ( 0UL )
#define portMPU_MAIR_ATTR4_MASK               ( 0x000000ff )

#define portMPU_MAIR_ATTR5_POS                ( 8UL )
#define portMPU_MAIR_ATTR5_MASK               ( 0x0000ff00 )

#define portMPU_MAIR_ATTR6_POS                ( 16UL )
#define portMPU_MAIR_ATTR6_MASK               ( 0x00ff0000 )

#define portMPU_MAIR_ATTR7_POS                ( 24UL )
#define portMPU_MAIR_ATTR7_MASK               ( 0xff000000 )

#define portMPU_RLAR_ATTR_INDEX0              ( 0UL << 1UL )
#define portMPU_RLAR_ATTR_INDEX1              ( 1UL << 1UL )
#define portMPU_RLAR_ATTR_INDEX2              ( 2UL << 1UL )
#define portMPU_RLAR_ATTR_INDEX3              ( 3UL << 1UL )
#define portMPU_RLAR_ATTR_INDEX4              ( 4UL << 1UL )
#define portMPU_RLAR_ATTR_INDEX5              ( 5UL << 1UL )
#define portMPU_RLAR_ATTR_INDEX6              ( 6UL << 1UL )
#define portMPU_RLAR_ATTR_INDEX7              ( 7UL << 1UL )

#define portMPU_RLAR_REGION_ENABLE            ( 1UL )

/* Enable privileged access to unmapped region. */
#define portMPU_PRIV_BACKGROUND_ENABLE_BIT    ( 1UL << 2UL )

/* Enable MPU. */
#define portMPU_ENABLE_BIT                    ( 1UL << 0UL )

/* Expected value of the portMPU_TYPE register. */
#define portEXPECTED_MPU_TYPE_VALUE           ( configTOTAL_MPU_REGIONS << 8UL )
/*-----------------------------------------------------------*/

/**
 * @brief The maximum 24-bit number.
 *
 * It is needed because the systick is a 24-bit counter.
 */
#define portMAX_24_BIT_NUMBER       ( 0xffffffUL )

/**
 * @brief 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    ( 94UL )
/*-----------------------------------------------------------*/

/**
 * @brief Constants required to set up the initial stack.
 */
#define portINITIAL_XPSR    ( 0x01000000 )

#if ( configRUN_FREERTOS_SECURE_ONLY == 1 )

/**
 * @brief Initial EXC_RETURN value.
 *
 *     FF         FF         FF         FD
 * 1111 1111  1111 1111  1111 1111  1111 1101
 *
 * Bit[6] - 1 --> The exception was taken from the Secure state.
 * Bit[5] - 1 --> Do not skip stacking of additional state context.
 * Bit[4] - 1 --> The PE did not allocate space on the stack for FP context.
 * Bit[3] - 1 --> Return to the Thread mode.
 * Bit[2] - 1 --> Restore registers from the process stack.
 * Bit[1] - 0 --> Reserved, 0.
 * Bit[0] - 1 --> The exception was taken to the Secure state.
 */
    #define portINITIAL_EXC_RETURN    ( 0xfffffffd )
#else

/**
 * @brief Initial EXC_RETURN value.
 *
 *     FF         FF         FF         BC
 * 1111 1111  1111 1111  1111 1111  1011 1100
 *
 * Bit[6] - 0 --> The exception was taken from the Non-Secure state.
 * Bit[5] - 1 --> Do not skip stacking of additional state context.
 * Bit[4] - 1 --> The PE did not allocate space on the stack for FP context.
 * Bit[3] - 1 --> Return to the Thread mode.
 * Bit[2] - 1 --> Restore registers from the process stack.
 * Bit[1] - 0 --> Reserved, 0.
 * Bit[0] - 0 --> The exception was taken to the Non-Secure state.
 */
    #define portINITIAL_EXC_RETURN    ( 0xffffffbc )
#endif /* configRUN_FREERTOS_SECURE_ONLY */

/**
 * @brief CONTROL register privileged bit mask.
 *
 * Bit[0] in CONTROL register tells the privilege:
 *  Bit[0] = 0 ==> The task is privileged.
 *  Bit[0] = 1 ==> The task is not privileged.
 */
#define portCONTROL_PRIVILEGED_MASK         ( 1UL << 0UL )

/**
 * @brief Initial CONTROL register values.
 */
#define portINITIAL_CONTROL_UNPRIVILEGED    ( 0x3 )
#define portINITIAL_CONTROL_PRIVILEGED      ( 0x2 )

/**
 * @brief Let the user override the default SysTick clock rate.  If defined by the
 * user, this symbol must equal the SysTick clock rate when the CLK bit is 0 in the
 * configuration register.
 */
#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_CONFIG    ( portNVIC_SYSTICK_CLK_BIT )
#else
    /* Select the option to clock SysTick not at the same frequency as the core. */
    #define portNVIC_SYSTICK_CLK_BIT_CONFIG    ( 0 )
#endif

/**
 * @brief Let the user override the pre-loading of the initial LR with the
 * address of prvTaskExitError() in case it messes up unwinding of the stack
 * in the debugger.
 */
#ifdef configTASK_RETURN_ADDRESS
    #define portTASK_RETURN_ADDRESS    configTASK_RETURN_ADDRESS
#else
    #define portTASK_RETURN_ADDRESS    prvTaskExitError
#endif

/**
 * @brief If portPRELOAD_REGISTERS then registers will be given an initial value
 * when a task is created. This helps in debugging at the cost of code size.
 */
#define portPRELOAD_REGISTERS    1

/**
 * @brief A task is created without a secure context, and must call
 * portALLOCATE_SECURE_CONTEXT() to give itself a secure context before it makes
 * any secure calls.
 */
#define portNO_SECURE_CONTEXT    0
/*-----------------------------------------------------------*/

/**
 * @brief Used to catch tasks that attempt to return from their implementing
 * function.
 */
static void prvTaskExitError( void );

#if ( configENABLE_MPU == 1 )

/**
 * @brief Setup the Memory Protection Unit (MPU).
 */
    static void prvSetupMPU( void ) PRIVILEGED_FUNCTION;
#endif /* configENABLE_MPU */

#if ( configENABLE_FPU == 1 )

/**
 * @brief Setup the Floating Point Unit (FPU).
 */
    static void prvSetupFPU( void ) PRIVILEGED_FUNCTION;
#endif /* configENABLE_FPU */

/**
 * @brief 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 ) PRIVILEGED_FUNCTION;

/**
 * @brief Checks whether the current execution context is interrupt.
 *
 * @return pdTRUE if the current execution context is interrupt, pdFALSE
 * otherwise.
 */
BaseType_t xPortIsInsideInterrupt( void );

/**
 * @brief Yield the processor.
 */
void vPortYield( void ) PRIVILEGED_FUNCTION;

/**
 * @brief Enter critical section.
 */
void vPortEnterCritical( void ) PRIVILEGED_FUNCTION;

/**
 * @brief Exit from critical section.
 */
void vPortExitCritical( void ) PRIVILEGED_FUNCTION;

/**
 * @brief SysTick handler.
 */
void SysTick_Handler( void ) PRIVILEGED_FUNCTION;

/**
 * @brief C part of SVC handler.
 */
portDONT_DISCARD void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) PRIVILEGED_FUNCTION;
/*-----------------------------------------------------------*/

/**
 * @brief Each task maintains its own interrupt status in the critical nesting
 * variable.
 */
PRIVILEGED_DATA static volatile uint32_t ulCriticalNesting = 0xaaaaaaaaUL;

#if ( configENABLE_TRUSTZONE == 1 )

/**
 * @brief Saved as part of the task context to indicate which context the
 * task is using on the secure side.
 */
    PRIVILEGED_DATA portDONT_DISCARD volatile SecureContextHandle_t xSecureContext = portNO_SECURE_CONTEXT;
#endif /* configENABLE_TRUSTZONE */

#if ( configUSE_TICKLESS_IDLE == 1 )

/**
 * @brief The number of SysTick increments that make up one tick period.
 */
    PRIVILEGED_DATA static uint32_t ulTimerCountsForOneTick = 0;

/**
 * @brief The maximum number of tick periods that can be suppressed is
 * limited by the 24 bit resolution of the SysTick timer.
 */
    PRIVILEGED_DATA static uint32_t xMaximumPossibleSuppressedTicks = 0;

/**
 * @brief Compensate for the CPU cycles that pass while the SysTick is
 * stopped (low power functionality only).
 */
    PRIVILEGED_DATA static uint32_t ulStoppedTimerCompensation = 0;
#endif /* configUSE_TICKLESS_IDLE */
/*-----------------------------------------------------------*/

#if ( configUSE_TICKLESS_IDLE == 1 )
    __attribute__( ( weak ) ) void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
    {
        uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements, ulSysTickDecrementsLeft;
        TickType_t xModifiableIdleTime;

        /* Make sure the SysTick reload value does not overflow the counter. */
        if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
        {
            xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
        }

        /* Enter a critical section but don't use the taskENTER_CRITICAL()
         * method as that will mask interrupts that should exit sleep mode. */
        __asm volatile ( "cpsid i" ::: "memory" );
        __asm volatile ( "dsb" );
        __asm volatile ( "isb" );

        /* If a context switch is pending or a task is waiting for the scheduler
         * to be unsuspended then abandon the low power entry. */
        if( eTaskConfirmSleepModeStatus() == eAbortSleep )
        {
            /* Re-enable interrupts - see comments above the cpsid instruction
             * above. */
            __asm volatile ( "cpsie i" ::: "memory" );
        }
        else
        {
            /* Stop the SysTick momentarily.  The time the SysTick is stopped for
             * is accounted for as best it can be, but using the tickless mode will
             * inevitably result in some tiny drift of the time maintained by the
             * kernel with respect to calendar time. */
            portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT_CONFIG | portNVIC_SYSTICK_INT_BIT );

            /* Use the SysTick current-value register to determine the number of
             * SysTick decrements remaining until the next tick interrupt.  If the
             * current-value register is zero, then there are actually
             * ulTimerCountsForOneTick decrements remaining, not zero, because the
             * SysTick requests the interrupt when decrementing from 1 to 0. */
            ulSysTickDecrementsLeft = portNVIC_SYSTICK_CURRENT_VALUE_REG;

            if( ulSysTickDecrementsLeft == 0 )
            {
                ulSysTickDecrementsLeft = ulTimerCountsForOneTick;
            }

            /* Calculate the reload value required to wait xExpectedIdleTime
             * tick periods.  -1 is used because this code normally executes part
             * way through the first tick period.  But if the SysTick IRQ is now
             * pending, then clear the IRQ, suppressing the first tick, and correct
             * the reload value to reflect that the second tick period is already
             * underway.  The expected idle time is always at least two ticks. */
            ulReloadValue = ulSysTickDecrementsLeft + ( ulTimerCountsForOneTick * ( xExpectedIdleTime - 1UL ) );

            if( ( portNVIC_INT_CTRL_REG & portNVIC_PEND_SYSTICK_SET_BIT ) != 0 )
            {
                portNVIC_INT_CTRL_REG = portNVIC_PEND_SYSTICK_CLEAR_BIT;
                ulReloadValue -= ulTimerCountsForOneTick;
            }

            if( ulReloadValue > ulStoppedTimerCompensation )
            {
                ulReloadValue -= ulStoppedTimerCompensation;
            }

            /* Set the new reload value. */
            portNVIC_SYSTICK_LOAD_REG = ulReloadValue;

            /* Clear the SysTick count flag and set the count value back to
             * zero. */
            portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;

            /* Restart SysTick. */
            portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;

            /* Sleep until something happens.  configPRE_SLEEP_PROCESSING() can
             * set its parameter to 0 to indicate that its implementation contains
             * its own wait for interrupt or wait for event instruction, and so wfi
             * should not be executed again.  However, the original expected idle
             * time variable must remain unmodified, so a copy is taken. */
            xModifiableIdleTime = xExpectedIdleTime;
            configPRE_SLEEP_PROCESSING( xModifiableIdleTime );

            if( xModifiableIdleTime > 0 )
            {
                __asm volatile ( "dsb" ::: "memory" );
                __asm volatile ( "wfi" );
                __asm volatile ( "isb" );
            }

            configPOST_SLEEP_PROCESSING( xExpectedIdleTime );

            /* Re-enable interrupts to allow the interrupt that brought the MCU
             * out of sleep mode to execute immediately.  See comments above
             * the cpsid instruction above. */
            __asm volatile ( "cpsie i" ::: "memory" );
            __asm volatile ( "dsb" );
            __asm volatile ( "isb" );

            /* Disable interrupts again because the clock is about to be stopped
             * and interrupts that execute while the clock is stopped will increase
             * any slippage between the time maintained by the RTOS and calendar
             * time. */
            __asm volatile ( "cpsid i" ::: "memory" );
            __asm volatile ( "dsb" );
            __asm volatile ( "isb" );

            /* Disable the SysTick clock without reading the
             * portNVIC_SYSTICK_CTRL_REG register to ensure the
             * portNVIC_SYSTICK_COUNT_FLAG_BIT is not cleared if it is set.  Again,
             * the time the SysTick is stopped for is accounted for as best it can
             * be, but using the tickless mode will inevitably result in some tiny
             * drift of the time maintained by the kernel with respect to calendar
             * time*/
            portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT_CONFIG | portNVIC_SYSTICK_INT_BIT );

            /* Determine whether the SysTick has already counted to zero. */
            if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
            {
                uint32_t ulCalculatedLoadValue;

                /* The tick interrupt ended the sleep (or is now pending), and
                 * a new tick period has started.  Reset portNVIC_SYSTICK_LOAD_REG
                 * with whatever remains of the new tick period. */
                ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );

                /* Don't allow a tiny value, or values that have somehow
                 * underflowed because the post sleep hook did something
                 * that took too long or because the SysTick current-value register
                 * is zero. */
                if( ( ulCalculatedLoadValue <= ulStoppedTimerCompensation ) || ( ulCalculatedLoadValue > ulTimerCountsForOneTick ) )
                {
                    ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL );
                }

                portNVIC_SYSTICK_LOAD_REG = ulCalculatedLoadValue;

                /* As the pending tick will be processed as soon as this
                 * function exits, the tick value maintained by the tick is stepped
                 * forward by one less than the time spent waiting. */
                ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
            }
            else
            {
                /* Something other than the tick interrupt ended the sleep. */

                /* Use the SysTick current-value register to determine the
                 * number of SysTick decrements remaining until the expected idle
                 * time would have ended. */
                ulSysTickDecrementsLeft = portNVIC_SYSTICK_CURRENT_VALUE_REG;
                #if ( portNVIC_SYSTICK_CLK_BIT_CONFIG != portNVIC_SYSTICK_CLK_BIT )
                {
                    /* If the SysTick is not using the core clock, the current-
                     * value register might still be zero here.  In that case, the
                     * SysTick didn't load from the reload register, and there are
                     * ulReloadValue decrements remaining in the expected idle
                     * time, not zero. */
                    if( ulSysTickDecrementsLeft == 0 )
                    {
                        ulSysTickDecrementsLeft = ulReloadValue;
                    }
                }
                #endif /* portNVIC_SYSTICK_CLK_BIT_CONFIG */

                /* Work out how long the sleep lasted rounded to complete tick
                 * periods (not the ulReload value which accounted for part
                 * ticks). */
                ulCompletedSysTickDecrements = ( xExpectedIdleTime * ulTimerCountsForOneTick ) - ulSysTickDecrementsLeft;

                /* How many complete tick periods passed while the processor
                 * was waiting? */
                ulCompleteTickPeriods = ulCompletedSysTickDecrements / ulTimerCountsForOneTick;

                /* The reload value is set to whatever fraction of a single tick
                 * period remains. */
                portNVIC_SYSTICK_LOAD_REG = ( ( ulCompleteTickPeriods + 1UL ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
            }

            /* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG again,
             * then set portNVIC_SYSTICK_LOAD_REG back to its standard value.  If
             * the SysTick is not using the core clock, temporarily configure it to
             * use the core clock.  This configuration forces the SysTick to load
             * from portNVIC_SYSTICK_LOAD_REG immediately instead of at the next
             * cycle of the other clock.  Then portNVIC_SYSTICK_LOAD_REG is ready
             * to receive the standard value immediately. */
            portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
            portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;
            #if ( portNVIC_SYSTICK_CLK_BIT_CONFIG == portNVIC_SYSTICK_CLK_BIT )
            {
                portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
            }
            #else
            {
                /* The temporary usage of the core clock has served its purpose,
                 * as described above.  Resume usage of the other clock. */
                portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT;

                if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
                {
                    /* The partial tick period already ended.  Be sure the SysTick
                     * counts it only once. */
                    portNVIC_SYSTICK_CURRENT_VALUE_REG = 0;
                }

                portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
                portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT_CONFIG | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;
            }
            #endif /* portNVIC_SYSTICK_CLK_BIT_CONFIG */

            /* Step the tick to account for any tick periods that elapsed. */
            vTaskStepTick( ulCompleteTickPeriods );

            /* Exit with interrupts enabled. */
            __asm volatile ( "cpsie i" ::: "memory" );
        }
    }
#endif /* configUSE_TICKLESS_IDLE */
/*-----------------------------------------------------------*/

__attribute__( ( weak ) ) void vPortSetupTimerInterrupt( void ) /* PRIVILEGED_FUNCTION */
{
    /* Calculate the constants required to configure the tick interrupt. */
    #if ( configUSE_TICKLESS_IDLE == 1 )
    {
        ulTimerCountsForOneTick = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ );
        xMaximumPossibleSuppressedTicks = portMAX_24_BIT_NUMBER / ulTimerCountsForOneTick;
        ulStoppedTimerCompensation = portMISSED_COUNTS_FACTOR / ( configCPU_CLOCK_HZ / configSYSTICK_CLOCK_HZ );
    }
    #endif /* configUSE_TICKLESS_IDLE */

    /* Stop and reset 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_CONFIG | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;
}
/*-----------------------------------------------------------*/

static void prvTaskExitError( void )
{
    volatile uint32_t ulDummy = 0UL;

    /* A function that implements a task must not exit or attempt to return to
     * its caller as there is nothing to return to. If a task wants to exit it
     * should instead call vTaskDelete( NULL ). Artificially force an assert()
     * to be triggered if configASSERT() is defined, then stop here so
     * application writers can catch the error. */
    configASSERT( ulCriticalNesting == ~0UL );
    portDISABLE_INTERRUPTS();

    while( ulDummy == 0 )
    {
        /* This file calls prvTaskExitError() after the scheduler has been
         * started to remove a compiler warning about the function being
         * defined but never called.  ulDummy is used purely to quieten other
         * warnings about code appearing after this function is called - making
         * ulDummy volatile makes the compiler think the function could return
         * and therefore not output an 'unreachable code' warning for code that
         * appears after it. */
    }
}
/*-----------------------------------------------------------*/

#if ( configENABLE_MPU == 1 )
    static void prvSetupMPU( void ) /* PRIVILEGED_FUNCTION */
    {
        #if defined( __ARMCC_VERSION )

            /* Declaration when these variable are defined in code instead of being
             * exported from linker scripts. */
            extern uint32_t * __privileged_functions_start__;
            extern uint32_t * __privileged_functions_end__;
            extern uint32_t * __syscalls_flash_start__;
            extern uint32_t * __syscalls_flash_end__;
            extern uint32_t * __unprivileged_flash_start__;
            extern uint32_t * __unprivileged_flash_end__;
            extern uint32_t * __privileged_sram_start__;
            extern uint32_t * __privileged_sram_end__;
        #else /* if defined( __ARMCC_VERSION ) */
            /* Declaration when these variable are exported from linker scripts. */
            extern uint32_t __privileged_functions_start__[];
            extern uint32_t __privileged_functions_end__[];
            extern uint32_t __syscalls_flash_start__[];
            extern uint32_t __syscalls_flash_end__[];
            extern uint32_t __unprivileged_flash_start__[];
            extern uint32_t __unprivileged_flash_end__[];
            extern uint32_t __privileged_sram_start__[];
            extern uint32_t __privileged_sram_end__[];
        #endif /* defined( __ARMCC_VERSION ) */

        /* 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 that the MPU is present. */
        if( portMPU_TYPE_REG == portEXPECTED_MPU_TYPE_VALUE )
        {
            /* MAIR0 - Index 0. */
            portMPU_MAIR0_REG |= ( ( portMPU_NORMAL_MEMORY_BUFFERABLE_CACHEABLE << portMPU_MAIR_ATTR0_POS ) & portMPU_MAIR_ATTR0_MASK );
            /* MAIR0 - Index 1. */
            portMPU_MAIR0_REG |= ( ( portMPU_DEVICE_MEMORY_nGnRE << portMPU_MAIR_ATTR1_POS ) & portMPU_MAIR_ATTR1_MASK );

            /* Setup privileged flash as Read Only so that privileged tasks can
             * read it but not modify. */
            portMPU_RNR_REG = portPRIVILEGED_FLASH_REGION;
            portMPU_RBAR_REG = ( ( ( uint32_t ) __privileged_functions_start__ ) & portMPU_RBAR_ADDRESS_MASK ) |
                               ( portMPU_REGION_NON_SHAREABLE ) |
                               ( portMPU_REGION_PRIVILEGED_READ_ONLY );
            portMPU_RLAR_REG = ( ( ( uint32_t ) __privileged_functions_end__ ) & portMPU_RLAR_ADDRESS_MASK ) |
                               ( portMPU_RLAR_ATTR_INDEX0 ) |
                               ( portMPU_RLAR_REGION_ENABLE );

            /* Setup unprivileged flash as Read Only by both privileged and
             * unprivileged tasks. All tasks can read it but no-one can modify. */
            portMPU_RNR_REG = portUNPRIVILEGED_FLASH_REGION;
            portMPU_RBAR_REG = ( ( ( uint32_t ) __unprivileged_flash_start__ ) & portMPU_RBAR_ADDRESS_MASK ) |
                               ( portMPU_REGION_NON_SHAREABLE ) |
                               ( portMPU_REGION_READ_ONLY );
            portMPU_RLAR_REG = ( ( ( uint32_t ) __unprivileged_flash_end__ ) & portMPU_RLAR_ADDRESS_MASK ) |
                               ( portMPU_RLAR_ATTR_INDEX0 ) |
                               ( portMPU_RLAR_REGION_ENABLE );

            /* Setup unprivileged syscalls flash as Read Only by both privileged
             * and unprivileged tasks. All tasks can read it but no-one can modify. */
            portMPU_RNR_REG = portUNPRIVILEGED_SYSCALLS_REGION;
            portMPU_RBAR_REG = ( ( ( uint32_t ) __syscalls_flash_start__ ) & portMPU_RBAR_ADDRESS_MASK ) |
                               ( portMPU_REGION_NON_SHAREABLE ) |
                               ( portMPU_REGION_READ_ONLY );
            portMPU_RLAR_REG = ( ( ( uint32_t ) __syscalls_flash_end__ ) & portMPU_RLAR_ADDRESS_MASK ) |
                               ( portMPU_RLAR_ATTR_INDEX0 ) |
                               ( portMPU_RLAR_REGION_ENABLE );

            /* Setup RAM containing kernel data for privileged access only. */
            portMPU_RNR_REG = portPRIVILEGED_RAM_REGION;
            portMPU_RBAR_REG = ( ( ( uint32_t ) __privileged_sram_start__ ) & portMPU_RBAR_ADDRESS_MASK ) |
                               ( portMPU_REGION_NON_SHAREABLE ) |
                               ( portMPU_REGION_PRIVILEGED_READ_WRITE ) |
                               ( portMPU_REGION_EXECUTE_NEVER );
            portMPU_RLAR_REG = ( ( ( uint32_t ) __privileged_sram_end__ ) & portMPU_RLAR_ADDRESS_MASK ) |
                               ( portMPU_RLAR_ATTR_INDEX0 ) |
                               ( portMPU_RLAR_REGION_ENABLE );

            /* Enable mem fault. */
            portSCB_SYS_HANDLER_CTRL_STATE_REG |= portSCB_MEM_FAULT_ENABLE_BIT;

            /* Enable MPU with privileged background access i.e. unmapped
             * regions have privileged access. */
            portMPU_CTRL_REG |= ( portMPU_PRIV_BACKGROUND_ENABLE_BIT | portMPU_ENABLE_BIT );
        }
    }
#endif /* configENABLE_MPU */
/*-----------------------------------------------------------*/

#if ( configENABLE_FPU == 1 )
    static void prvSetupFPU( void ) /* PRIVILEGED_FUNCTION */
    {
        #if ( configENABLE_TRUSTZONE == 1 )
        {
            /* Enable non-secure access to the FPU. */
            SecureInit_EnableNSFPUAccess();
        }
        #endif /* configENABLE_TRUSTZONE */

        /* CP10 = 11 ==> Full access to FPU i.e. both privileged and
         * unprivileged code should be able to access FPU. CP11 should be
         * programmed to the same value as CP10. */
        *( portCPACR ) |= ( ( portCPACR_CP10_VALUE << portCPACR_CP10_POS ) |
                            ( portCPACR_CP11_VALUE << portCPACR_CP11_POS )
                            );

        /* ASPEN = 1 ==> Hardware should automatically preserve floating point
         * context on exception entry and restore on exception return.
         * LSPEN = 1 ==> Enable lazy context save of FP state. */
        *( portFPCCR ) |= ( portFPCCR_ASPEN_MASK | portFPCCR_LSPEN_MASK );
    }
#endif /* configENABLE_FPU */
/*-----------------------------------------------------------*/

void vPortYield( void ) /* PRIVILEGED_FUNCTION */
{
    /* Set a PendSV to request a context switch. */
    portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;

    /* Barriers are normally not required but do ensure the code is
     * completely within the specified behaviour for the architecture. */
    __asm volatile ( "dsb" ::: "memory" );
    __asm volatile ( "isb" );
}
/*-----------------------------------------------------------*/

void vPortEnterCritical( void ) /* PRIVILEGED_FUNCTION */
{
    portDISABLE_INTERRUPTS();
    ulCriticalNesting++;

    /* 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" );
}
/*-----------------------------------------------------------*/

void vPortExitCritical( void ) /* PRIVILEGED_FUNCTION */
{
    configASSERT( ulCriticalNesting );
    ulCriticalNesting--;

    if( ulCriticalNesting == 0 )
    {
        portENABLE_INTERRUPTS();
    }
}
/*-----------------------------------------------------------*/

void SysTick_Handler( void ) /* PRIVILEGED_FUNCTION */
{
    uint32_t ulPreviousMask;

    ulPreviousMask = 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( ulPreviousMask );
}
/*-----------------------------------------------------------*/

void vPortSVCHandler_C( uint32_t * pulCallerStackAddress ) /* PRIVILEGED_FUNCTION portDONT_DISCARD */
{
    #if ( configENABLE_MPU == 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 /* defined( __ARMCC_VERSION ) */
    #endif /* configENABLE_MPU */

    uint32_t ulPC;

    #if ( configENABLE_TRUSTZONE == 1 )
        uint32_t ulR0, ulR1;
        extern TaskHandle_t pxCurrentTCB;
        #if ( configENABLE_MPU == 1 )
            uint32_t ulControl, ulIsTaskPrivileged;
        #endif /* configENABLE_MPU */
    #endif /* configENABLE_TRUSTZONE */
    uint8_t ucSVCNumber;

    /* Register are stored on the stack in the following order - R0, R1, R2, R3,
     * R12, LR, PC, xPSR. */
    ulPC = pulCallerStackAddress[ 6 ];
    ucSVCNumber = ( ( uint8_t * ) ulPC )[ -2 ];

    switch( ucSVCNumber )
    {
        #if ( configENABLE_TRUSTZONE == 1 )
            case portSVC_ALLOCATE_SECURE_CONTEXT:

                /* R0 contains the stack size passed as parameter to the
                 * vPortAllocateSecureContext function. */
                ulR0 = pulCallerStackAddress[ 0 ];

                #if ( configENABLE_MPU == 1 )
                {
                    /* Read the CONTROL register value. */
                    __asm volatile ( "mrs %0, control"  : "=r" ( ulControl ) );

                    /* The task that raised the SVC is privileged if Bit[0]
                     * in the CONTROL register is 0. */
                    ulIsTaskPrivileged = ( ( ulControl & portCONTROL_PRIVILEGED_MASK ) == 0 );

                    /* Allocate and load a context for the secure task. */
                    xSecureContext = SecureContext_AllocateContext( ulR0, ulIsTaskPrivileged, pxCurrentTCB );
                }
                #else /* if ( configENABLE_MPU == 1 ) */
                {
                    /* Allocate and load a context for the secure task. */
                    xSecureContext = SecureContext_AllocateContext( ulR0, pxCurrentTCB );
                }
                #endif /* configENABLE_MPU */

                configASSERT( xSecureContext != securecontextINVALID_CONTEXT_ID );
                SecureContext_LoadContext( xSecureContext, pxCurrentTCB );
                break;

            case portSVC_FREE_SECURE_CONTEXT:

                /* R0 contains TCB being freed and R1 contains the secure
                 * context handle to be freed. */
                ulR0 = pulCallerStackAddress[ 0 ];
                ulR1 = pulCallerStackAddress[ 1 ];

                /* Free the secure context. */
                SecureContext_FreeContext( ( SecureContextHandle_t ) ulR1, ( void * ) ulR0 );
                break;
        #endif /* configENABLE_TRUSTZONE */

        case portSVC_START_SCHEDULER:
            #if ( configENABLE_TRUSTZONE == 1 )
            {
                /* De-prioritize the non-secure exceptions so that the
                 * non-secure pendSV runs at the lowest priority. */
                SecureInit_DePrioritizeNSExceptions();

                /* Initialize the secure context management system. */
                SecureContext_Init();
            }
            #endif /* configENABLE_TRUSTZONE */

            #if ( configENABLE_FPU == 1 )
            {
                /* Setup the Floating Point Unit (FPU). */
                prvSetupFPU();
            }
            #endif /* configENABLE_FPU */

            /* Setup the context of the first task so that the first task starts
             * executing. */
            vRestoreContextOfFirstTask();
            break;

            #if ( configENABLE_MPU == 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__ ) )
                    {
                        vRaisePrivilege();
                    }
                    break;
            #endif /* configENABLE_MPU */

        default:
            /* Incorrect SVC call. */
            configASSERT( pdFALSE );
    }
}
/*-----------------------------------------------------------*/
/* *INDENT-OFF* */
#if ( configENABLE_MPU == 1 )
    StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
                                         StackType_t * pxEndOfStack,
                                         TaskFunction_t pxCode,
                                         void * pvParameters,
                                         BaseType_t xRunPrivileged ) /* PRIVILEGED_FUNCTION */
#else
    StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
                                         StackType_t * pxEndOfStack,
                                         TaskFunction_t pxCode,
                                         void * pvParameters ) /* PRIVILEGED_FUNCTION */
#endif /* configENABLE_MPU */
/* *INDENT-ON* */
{
    /* Simulate the stack frame as it would be created by a context switch
     * interrupt. */
    #if ( portPRELOAD_REGISTERS == 0 )
    {
        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;                  /* PC */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) portTASK_RETURN_ADDRESS; /* LR */
        pxTopOfStack -= 5;                                       /* R12, R3, R2 and R1. */
        *pxTopOfStack = ( StackType_t ) pvParameters;            /* R0 */
        pxTopOfStack -= 9;                                       /* R11..R4, EXC_RETURN. */
        *pxTopOfStack = portINITIAL_EXC_RETURN;

        #if ( configENABLE_MPU == 1 )
        {
            pxTopOfStack--;

            if( xRunPrivileged == pdTRUE )
            {
                *pxTopOfStack = portINITIAL_CONTROL_PRIVILEGED; /* Slot used to hold this task's CONTROL value. */
            }
            else
            {
                *pxTopOfStack = portINITIAL_CONTROL_UNPRIVILEGED; /* Slot used to hold this task's CONTROL value. */
            }
        }
        #endif /* configENABLE_MPU */

        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) pxEndOfStack; /* Slot used to hold this task's PSPLIM value. */

        #if ( configENABLE_TRUSTZONE == 1 )
        {
            pxTopOfStack--;
            *pxTopOfStack = portNO_SECURE_CONTEXT; /* Slot used to hold this task's xSecureContext value. */
        }
        #endif /* configENABLE_TRUSTZONE */
    }
    #else /* portPRELOAD_REGISTERS */
    {
        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;                  /* PC */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) portTASK_RETURN_ADDRESS; /* LR */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x12121212UL;            /* R12 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x03030303UL;            /* R3 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x02020202UL;            /* R2 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x01010101UL;            /* R1 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) pvParameters;            /* R0 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x11111111UL;            /* R11 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x10101010UL;            /* R10 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x09090909UL;            /* R09 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x08080808UL;            /* R08 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x07070707UL;            /* R07 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x06060606UL;            /* R06 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x05050505UL;            /* R05 */
        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) 0x04040404UL;            /* R04 */
        pxTopOfStack--;
        *pxTopOfStack = portINITIAL_EXC_RETURN;                  /* EXC_RETURN */

        #if ( configENABLE_MPU == 1 )
        {
            pxTopOfStack--;

            if( xRunPrivileged == pdTRUE )
            {
                *pxTopOfStack = portINITIAL_CONTROL_PRIVILEGED; /* Slot used to hold this task's CONTROL value. */
            }
            else
            {
                *pxTopOfStack = portINITIAL_CONTROL_UNPRIVILEGED; /* Slot used to hold this task's CONTROL value. */
            }
        }
        #endif /* configENABLE_MPU */

        pxTopOfStack--;
        *pxTopOfStack = ( StackType_t ) pxEndOfStack; /* Slot used to hold this task's PSPLIM value. */

        #if ( configENABLE_TRUSTZONE == 1 )
        {
            pxTopOfStack--;
            *pxTopOfStack = portNO_SECURE_CONTEXT; /* Slot used to hold this task's xSecureContext value. */
        }
        #endif /* configENABLE_TRUSTZONE */
    }
    #endif /* portPRELOAD_REGISTERS */

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

BaseType_t xPortStartScheduler( void ) /* PRIVILEGED_FUNCTION */
{
    /* Make PendSV, CallSV and SysTick the same priority as the kernel. */
    portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
    portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;

    #if ( configENABLE_MPU == 1 )
    {
        /* Setup the Memory Protection Unit (MPU). */
        prvSetupMPU();
    }
    #endif /* configENABLE_MPU */

    /* Start the timer that generates the tick ISR. Interrupts are disabled
     * here already. */
    vPortSetupTimerInterrupt();

    /* Initialize the critical nesting count ready for the first task. */
    ulCriticalNesting = 0;

    /* Start the first task. */
    vStartFirstTask();

    /* Should never get here as the tasks will now be executing. Call the task
     * exit error function to prevent compiler warnings about a static function
     * not being called in the case that the application writer overrides this
     * functionality by defining configTASK_RETURN_ADDRESS. Call
     * vTaskSwitchContext() so link time optimization does not remove the
     * symbol. */
    vTaskSwitchContext();
    prvTaskExitError();

    /* Should not get here. */
    return 0;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void ) /* PRIVILEGED_FUNCTION */
{
    /* Not implemented in ports where there is nothing to return to.
     * Artificially force an assert. */
    configASSERT( ulCriticalNesting == 1000UL );
}
/*-----------------------------------------------------------*/

#if ( configENABLE_MPU == 1 )
    void vPortStoreTaskMPUSettings( xMPU_SETTINGS * xMPUSettings,
                                    const struct xMEMORY_REGION * const xRegions,
                                    StackType_t * pxBottomOfStack,
                                    uint32_t ulStackDepth )
    {
        uint32_t ulRegionStartAddress, ulRegionEndAddress, ulRegionNumber;
        int32_t lIndex = 0;

        #if defined( __ARMCC_VERSION )

            /* Declaration when these variable are defined in code instead of being
             * exported from linker scripts. */
            extern uint32_t * __privileged_sram_start__;
            extern uint32_t * __privileged_sram_end__;
        #else
            /* Declaration when these variable are exported from linker scripts. */
            extern uint32_t __privileged_sram_start__[];
            extern uint32_t __privileged_sram_end__[];
        #endif /* defined( __ARMCC_VERSION ) */

        /* Setup MAIR0. */
        xMPUSettings->ulMAIR0 = ( ( portMPU_NORMAL_MEMORY_BUFFERABLE_CACHEABLE << portMPU_MAIR_ATTR0_POS ) & portMPU_MAIR_ATTR0_MASK );
        xMPUSettings->ulMAIR0 |= ( ( portMPU_DEVICE_MEMORY_nGnRE << portMPU_MAIR_ATTR1_POS ) & portMPU_MAIR_ATTR1_MASK );

        /* 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 )
        {
            ulRegionStartAddress = ( uint32_t ) pxBottomOfStack;
            ulRegionEndAddress = ( uint32_t ) pxBottomOfStack + ( ulStackDepth * ( uint32_t ) sizeof( StackType_t ) ) - 1;

            /* If the stack is within the privileged SRAM, do not protect it
             * using a separate MPU region. This is needed because privileged
             * SRAM is already protected using an MPU region and ARMv8-M does
             * not allow overlapping MPU regions. */
            if( ( ulRegionStartAddress >= ( uint32_t ) __privileged_sram_start__ ) &&
                ( ulRegionEndAddress <= ( uint32_t ) __privileged_sram_end__ ) )
            {
                xMPUSettings->xRegionsSettings[ 0 ].ulRBAR = 0;
                xMPUSettings->xRegionsSettings[ 0 ].ulRLAR = 0;
            }
            else
            {
                /* Define the region that allows access to the stack. */
                ulRegionStartAddress &= portMPU_RBAR_ADDRESS_MASK;
                ulRegionEndAddress &= portMPU_RLAR_ADDRESS_MASK;

                xMPUSettings->xRegionsSettings[ 0 ].ulRBAR = ( ulRegionStartAddress ) |
                                                             ( portMPU_REGION_NON_SHAREABLE ) |
                                                             ( portMPU_REGION_READ_WRITE ) |
                                                             ( portMPU_REGION_EXECUTE_NEVER );

                xMPUSettings->xRegionsSettings[ 0 ].ulRLAR = ( ulRegionEndAddress ) |
                                                             ( portMPU_RLAR_ATTR_INDEX0 ) |
                                                             ( portMPU_RLAR_REGION_ENABLE );
            }
        }

        /* User supplied configurable regions. */
        for( ulRegionNumber = 1; ulRegionNumber <= portNUM_CONFIGURABLE_REGIONS; ulRegionNumber++ )
        {
            /* If xRegions is NULL i.e. the task has not specified any MPU
             * region, the else part ensures that all the configurable MPU
             * regions are invalidated. */
            if( ( xRegions != NULL ) && ( xRegions[ lIndex ].ulLengthInBytes > 0UL ) )
            {
                /* Translate the generic region definition contained in xRegions
                 * into the ARMv8 specific MPU settings that are then stored in
                 * xMPUSettings. */
                ulRegionStartAddress = ( ( uint32_t ) xRegions[ lIndex ].pvBaseAddress ) & portMPU_RBAR_ADDRESS_MASK;
                ulRegionEndAddress = ( uint32_t ) xRegions[ lIndex ].pvBaseAddress + xRegions[ lIndex ].ulLengthInBytes - 1;
                ulRegionEndAddress &= portMPU_RLAR_ADDRESS_MASK;

                /* Start address. */
                xMPUSettings->xRegionsSettings[ ulRegionNumber ].ulRBAR = ( ulRegionStartAddress ) |
                                                                          ( portMPU_REGION_NON_SHAREABLE );

                /* RO/RW. */
                if( ( xRegions[ lIndex ].ulParameters & tskMPU_REGION_READ_ONLY ) != 0 )
                {
                    xMPUSettings->xRegionsSettings[ ulRegionNumber ].ulRBAR |= ( portMPU_REGION_READ_ONLY );
                }
                else
                {
                    xMPUSettings->xRegionsSettings[ ulRegionNumber ].ulRBAR |= ( portMPU_REGION_READ_WRITE );
                }

                /* XN. */
                if( ( xRegions[ lIndex ].ulParameters & tskMPU_REGION_EXECUTE_NEVER ) != 0 )
                {
                    xMPUSettings->xRegionsSettings[ ulRegionNumber ].ulRBAR |= ( portMPU_REGION_EXECUTE_NEVER );
                }

                /* End Address. */
                xMPUSettings->xRegionsSettings[ ulRegionNumber ].ulRLAR = ( ulRegionEndAddress ) |
                                                                          ( portMPU_RLAR_REGION_ENABLE );

                /* Normal memory/ Device memory. */
                if( ( xRegions[ lIndex ].ulParameters & tskMPU_REGION_DEVICE_MEMORY ) != 0 )
                {
                    /* Attr1 in MAIR0 is configured as device memory. */
                    xMPUSettings->xRegionsSettings[ ulRegionNumber ].ulRLAR |= portMPU_RLAR_ATTR_INDEX1;
                }
                else
                {
                    /* Attr0 in MAIR0 is configured as normal memory. */
                    xMPUSettings->xRegionsSettings[ ulRegionNumber ].ulRLAR |= portMPU_RLAR_ATTR_INDEX0;
                }
            }
            else
            {
                /* Invalidate the region. */
                xMPUSettings->xRegionsSettings[ ulRegionNumber ].ulRBAR = 0UL;
                xMPUSettings->xRegionsSettings[ ulRegionNumber ].ulRLAR = 0UL;
            }

            lIndex++;
        }
    }
#endif /* configENABLE_MPU */
/*-----------------------------------------------------------*/

BaseType_t xPortIsInsideInterrupt( void )
{
    uint32_t ulCurrentInterrupt;
    BaseType_t xReturn;

    /* Obtain the number of the currently executing interrupt. Interrupt Program
     * Status Register (IPSR) holds the exception number of the currently-executing
     * exception or zero for Thread mode.*/
    __asm volatile ( "mrs %0, ipsr" : "=r" ( ulCurrentInterrupt )::"memory" );

    if( ulCurrentInterrupt == 0 )
    {
        xReturn = pdFALSE;
    }
    else
    {
        xReturn = pdTRUE;
    }

    return xReturn;
}
/*-----------------------------------------------------------*/