/*
 * 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
 *
 */

/*-----------------------------------------------------------
* Implementation of functions defined in portable.h for the SH2A port.
*----------------------------------------------------------*/

/* Standard C includes. */
#include "limits.h"

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

/* Library includes. */
#include "string.h"

/* Hardware specifics. */
#include "iodefine.h"

/*-----------------------------------------------------------*/

/* Tasks should start with interrupts enabled and in Supervisor mode, therefore
 * PSW is set with U and I set, and PM and IPL clear. */
#define portINITIAL_PSW    ( ( StackType_t ) 0x00030000 )

/* The peripheral clock is divided by this value before being supplying the
 * CMT. */
#if ( configUSE_TICKLESS_IDLE == 0 )
    /* If tickless idle is not used then the divisor can be fixed. */
    #define portCLOCK_DIVISOR    8UL
#elif ( configPERIPHERAL_CLOCK_HZ >= 12000000 )
    #define portCLOCK_DIVISOR    512UL
#elif ( configPERIPHERAL_CLOCK_HZ >= 6000000 )
    #define portCLOCK_DIVISOR    128UL
#elif ( configPERIPHERAL_CLOCK_HZ >= 1000000 )
    #define portCLOCK_DIVISOR    32UL
#else
    #define portCLOCK_DIVISOR    8UL
#endif

/* These macros allow a critical section to be added around the call to
 * xTaskIncrementTick(), which is only ever called from interrupts at the kernel
 * priority - ie a known priority.  Therefore these local macros are a slight
 * optimisation compared to calling the global SET/CLEAR_INTERRUPT_MASK macros,
 * which would require the old IPL to be read first and stored in a local variable. */
#define portDISABLE_INTERRUPTS_FROM_KERNEL_ISR()    __asm volatile ( "MVTIPL	%0"::"i" ( configMAX_SYSCALL_INTERRUPT_PRIORITY ) )
#define portENABLE_INTERRUPTS_FROM_KERNEL_ISR()     __asm volatile ( "MVTIPL	%0"::"i" ( configKERNEL_INTERRUPT_PRIORITY ) )

/* Keys required to lock and unlock access to certain system registers
 * respectively. */
#define portUNLOCK_KEY    0xA50B
#define portLOCK_KEY      0xA500

/*-----------------------------------------------------------*/

/*
 * Function to start the first task executing - written in asm code as direct
 * access to registers is required.
 */
static void prvStartFirstTask( void ) __attribute__( ( naked ) );

/*
 * Software interrupt handler.  Performs the actual context switch (saving and
 * restoring of registers).  Written in asm code as direct register access is
 * required.
 */
void vPortSoftwareInterruptISR( void ) __attribute__( ( naked ) );

/*
 * The tick interrupt handler.
 */
void vPortTickISR( void ) __attribute__( ( interrupt ) );

/*
 * Sets up the periodic ISR used for the RTOS tick using the CMT.
 * The application writer can define configSETUP_TICK_INTERRUPT() (in
 * FreeRTOSConfig.h) such that their own tick interrupt configuration is used
 * in place of prvSetupTimerInterrupt().
 */
static void prvSetupTimerInterrupt( void );
#ifndef configSETUP_TICK_INTERRUPT

/* The user has not provided their own tick interrupt configuration so use
 * the definition in this file (which uses the interval timer). */
    #define configSETUP_TICK_INTERRUPT()    prvSetupTimerInterrupt()
#endif /* configSETUP_TICK_INTERRUPT */

/*
 * Called after the sleep mode registers have been configured, prvSleep()
 * executes the pre and post sleep macros, and actually calls the wait
 * instruction.
 */
#if configUSE_TICKLESS_IDLE == 1
    static void prvSleep( TickType_t xExpectedIdleTime );
#endif /* configUSE_TICKLESS_IDLE */

/*-----------------------------------------------------------*/

/* Used in the context save and restore code. */
extern void *         pxCurrentTCB;

/* Calculate how many clock increments make up a single tick period. */
static const uint32_t ulMatchValueForOneTick                = ( ( configPERIPHERAL_CLOCK_HZ / portCLOCK_DIVISOR ) / configTICK_RATE_HZ );

#if configUSE_TICKLESS_IDLE == 1

/* Holds the maximum number of ticks that can be suppressed - which is
 * basically how far into the future an interrupt can be generated. Set
 * during initialisation.  This is the maximum possible value that the
 * compare match register can hold divided by ulMatchValueForOneTick. */
    static const TickType_t xMaximumPossibleSuppressedTicks = USHRT_MAX / ( ( configPERIPHERAL_CLOCK_HZ / portCLOCK_DIVISOR ) / configTICK_RATE_HZ );

/* Flag set from the tick interrupt to allow the sleep processing to know if
 * sleep mode was exited because of a tick interrupt, or an interrupt
 * generated by something else. */
    static volatile uint32_t ulTickFlag                     = pdFALSE;

/* The CMT counter is stopped temporarily each time it is re-programmed.
 * The following constant offsets the CMT counter match value by the number of
 * CMT	counts that would typically be missed while the counter was stopped to
 * compensate for the lost time.  The large difference between the divided CMT
 * clock and the CPU clock means it is likely ulStoppedTimerCompensation will
 * equal zero - and be optimised away. */
    static const uint32_t ulStoppedTimerCompensation        = 100UL / ( configCPU_CLOCK_HZ / ( configPERIPHERAL_CLOCK_HZ / portCLOCK_DIVISOR ) );

#endif /* if configUSE_TICKLESS_IDLE == 1 */

/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
                                     TaskFunction_t pxCode,
                                     void * pvParameters )
{
    /* Offset to end up on 8 byte boundary. */
    pxTopOfStack--;

    /* R0 is not included as it is the stack pointer. */
    *pxTopOfStack = 0x00;
    pxTopOfStack--;
    *pxTopOfStack = 0x00;
    pxTopOfStack--;
    *pxTopOfStack = portINITIAL_PSW;
    pxTopOfStack--;
    *pxTopOfStack = ( StackType_t ) pxCode;

    /* When debugging it can be useful if every register is set to a known
     * value.  Otherwise code space can be saved by just setting the registers
     * that need to be set. */
    #ifdef USE_FULL_REGISTER_INITIALISATION
        {
            pxTopOfStack--;
            *pxTopOfStack = 0x12345678; /* r15. */
            pxTopOfStack--;
            *pxTopOfStack = 0xaaaabbbb;
            pxTopOfStack--;
            *pxTopOfStack = 0xdddddddd;
            pxTopOfStack--;
            *pxTopOfStack = 0xcccccccc;
            pxTopOfStack--;
            *pxTopOfStack = 0xbbbbbbbb;
            pxTopOfStack--;
            *pxTopOfStack = 0xaaaaaaaa;
            pxTopOfStack--;
            *pxTopOfStack = 0x99999999;
            pxTopOfStack--;
            *pxTopOfStack = 0x88888888;
            pxTopOfStack--;
            *pxTopOfStack = 0x77777777;
            pxTopOfStack--;
            *pxTopOfStack = 0x66666666;
            pxTopOfStack--;
            *pxTopOfStack = 0x55555555;
            pxTopOfStack--;
            *pxTopOfStack = 0x44444444;
            pxTopOfStack--;
            *pxTopOfStack = 0x33333333;
            pxTopOfStack--;
            *pxTopOfStack = 0x22222222;
            pxTopOfStack--;
        }
    #else  /* ifdef USE_FULL_REGISTER_INITIALISATION */
        {
            /* Leave space for the registers that will get popped from the stack
             * when the task first starts executing. */
            pxTopOfStack -= 15;
        }
    #endif /* ifdef USE_FULL_REGISTER_INITIALISATION */

    *pxTopOfStack = ( StackType_t ) pvParameters; /* R1 */
    pxTopOfStack--;
    *pxTopOfStack = 0x12345678;                   /* Accumulator. */
    pxTopOfStack--;
    *pxTopOfStack = 0x87654321;                   /* Accumulator. */

    return pxTopOfStack;
}
/*-----------------------------------------------------------*/

BaseType_t xPortStartScheduler( void )
{
    /* Use pxCurrentTCB just so it does not get optimised away. */
    if( pxCurrentTCB != NULL )
    {
        /* Call an application function to set up the timer that will generate
         * the tick interrupt.  This way the application can decide which
         * peripheral to use.  If tickless mode is used then the default
         * implementation defined in this file (which uses CMT0) should not be
         * overridden. */
        configSETUP_TICK_INTERRUPT();

        /* Enable the software interrupt. */
        _IEN( _ICU_SWINT ) = 1;

        /* Ensure the software interrupt is clear. */
        _IR( _ICU_SWINT )  = 0;

        /* Ensure the software interrupt is set to the kernel priority. */
        _IPR( _ICU_SWINT ) = configKERNEL_INTERRUPT_PRIORITY;

        /* Start the first task. */
        prvStartFirstTask();
    }

    /* Execution should not reach here as the tasks are now running!
     * prvSetupTimerInterrupt() is called here to prevent the compiler outputting
     * a warning about a statically declared function not being referenced in the
     * case that the application writer has provided their own tick interrupt
     * configuration routine (and defined configSETUP_TICK_INTERRUPT() such that
     * their own routine will be called in place of prvSetupTimerInterrupt()). */
    prvSetupTimerInterrupt();

    /* Should not get here. */
    return pdFAIL;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
    /* Not implemented in ports where there is nothing to return to.
     * Artificially force an assert. */
    configASSERT( pxCurrentTCB == NULL );
}
/*-----------------------------------------------------------*/

static void prvStartFirstTask( void )
{
    __asm volatile
    (

        /* When starting the scheduler there is nothing that needs moving to the
         * interrupt stack because the function is not called from an interrupt.
         * Just ensure the current stack is the user stack. */
        "SETPSW		U						\n"\


        /* Obtain the location of the stack associated with which ever task
         * pxCurrentTCB is currently pointing to. */
        "MOV.L		#_pxCurrentTCB, R15		\n"\
        "MOV.L		[R15], R15				\n"\
        "MOV.L		[R15], R0				\n"\


        /* Restore the registers from the stack of the task pointed to by
         * pxCurrentTCB. */
        "POP		R15						\n"\

        /* Accumulator low 32 bits. */
        "MVTACLO	R15 					\n"\
        "POP		R15						\n"\

        /* Accumulator high 32 bits. */
        "MVTACHI	R15 					\n"\

        /* R1 to R15 - R0 is not included as it is the SP. */
        "POPM		R1-R15 					\n"\

        /* This pops the remaining registers. */
        "RTE								\n"\
        "NOP								\n"\
        "NOP								\n"
    );
}
/*-----------------------------------------------------------*/

void vPortSoftwareInterruptISR( void )
{
    __asm volatile
    (
        /* Re-enable interrupts. */
        "SETPSW		I							\n"\


        /* Move the data that was automatically pushed onto the interrupt stack when
         * the interrupt occurred from the interrupt stack to the user stack.
         *
         * R15 is saved before it is clobbered. */
        "PUSH.L		R15							\n"\

        /* Read the user stack pointer. */
        "MVFC		USP, R15					\n"\

        /* Move the address down to the data being moved. */
        "SUB		#12, R15					\n"\
        "MVTC		R15, USP					\n"\

        /* Copy the data across, R15, then PC, then PSW. */
        "MOV.L		[ R0 ], [ R15 ]				\n"\
        "MOV.L 		4[ R0 ], 4[ R15 ]			\n"\
        "MOV.L		8[ R0 ], 8[ R15 ]			\n"\

        /* Move the interrupt stack pointer to its new correct position. */
        "ADD		#12, R0						\n"\

        /* All the rest of the registers are saved directly to the user stack. */
        "SETPSW		U							\n"\

        /* Save the rest of the general registers (R15 has been saved already). */
        "PUSHM		R1-R14						\n"\

        /* Save the accumulator. */
        "MVFACHI 	R15							\n"\
        "PUSH.L		R15							\n"\

        /* Middle word. */
        "MVFACMI	R15							\n"\

        /* Shifted left as it is restored to the low order word. */
        "SHLL		#16, R15					\n"\
        "PUSH.L		R15							\n"\

        /* Save the stack pointer to the TCB. */
        "MOV.L		#_pxCurrentTCB, R15			\n"\
        "MOV.L		[ R15 ], R15				\n"\
        "MOV.L		R0, [ R15 ]					\n"\


        /* Ensure the interrupt mask is set to the syscall priority while the kernel
         * structures are being accessed. */
        "MVTIPL		%0 							\n"\

        /* Select the next task to run. */
        "BSR.A		_vTaskSwitchContext			\n"\

        /* Reset the interrupt mask as no more data structure access is required. */
        "MVTIPL		%1							\n"\


        /* Load the stack pointer of the task that is now selected as the Running
         * state task from its TCB. */
        "MOV.L		#_pxCurrentTCB,R15			\n"\
        "MOV.L		[ R15 ], R15				\n"\
        "MOV.L		[ R15 ], R0					\n"\


        /* Restore the context of the new task.  The PSW (Program Status Word) and
         * PC will be popped by the RTE instruction. */
        "POP		R15							\n"\
        "MVTACLO 	R15							\n"\
        "POP		R15							\n"\
        "MVTACHI 	R15							\n"\
        "POPM		R1-R15						\n"\
        "RTE									\n"\
        "NOP									\n"\
        "NOP									  "
        ::"i" ( configMAX_SYSCALL_INTERRUPT_PRIORITY ), "i" ( configKERNEL_INTERRUPT_PRIORITY )
    );
}
/*-----------------------------------------------------------*/

void vPortTickISR( void )
{
    /* Re-enabled interrupts. */
    __asm volatile ( "SETPSW	I");

    /* Increment the tick, and perform any processing the new tick value
     * necessitates.  Ensure IPL is at the max syscall value first. */
    portDISABLE_INTERRUPTS_FROM_KERNEL_ISR();
    {
        if( xTaskIncrementTick() != pdFALSE )
        {
            taskYIELD();
        }
    }
    portENABLE_INTERRUPTS_FROM_KERNEL_ISR();

    #if configUSE_TICKLESS_IDLE == 1
        {
            /* The CPU woke because of a tick. */
            ulTickFlag = pdTRUE;

            /* If this is the first tick since exiting tickless mode then the CMT
             * compare match value needs resetting. */
            CMT0.CMCOR = ( uint16_t ) ulMatchValueForOneTick;
        }
    #endif
}
/*-----------------------------------------------------------*/

uint32_t ulPortGetIPL( void )
{
    __asm volatile
    (
        "MVFC	PSW, R1			\n"\
        "SHLR	#24, R1			\n"\
        "RTS					  "
    );

    /* This will never get executed, but keeps the compiler from complaining. */
    return 0;
}
/*-----------------------------------------------------------*/

void vPortSetIPL( uint32_t ulNewIPL )
{
    __asm volatile
    (
        "PUSH	R5				\n"\
        "MVFC	PSW, R5			\n"\
        "SHLL	#24, R1			\n"\
        "AND	#-0F000001H, R5 \n"\
        "OR		R1, R5			\n"\
        "MVTC	R5, PSW			\n"\
        "POP	R5				\n"\
        "RTS					  "
    );
}
/*-----------------------------------------------------------*/

static void prvSetupTimerInterrupt( void )
{
    /* Unlock. */
    SYSTEM.PRCR.WORD    = portUNLOCK_KEY;

    /* Enable CMT0. */
    MSTP( CMT0 )        = 0;

    /* Lock again. */
    SYSTEM.PRCR.WORD    = portLOCK_KEY;

    /* Interrupt on compare match. */
    CMT0.CMCR.BIT.CMIE  = 1;

    /* Set the compare match value. */
    CMT0.CMCOR          = ( uint16_t ) ulMatchValueForOneTick;

    /* Divide the PCLK. */
    #if portCLOCK_DIVISOR == 512
        {
            CMT0.CMCR.BIT.CKS = 3;
        }
    #elif portCLOCK_DIVISOR == 128
        {
            CMT0.CMCR.BIT.CKS = 2;
        }
    #elif portCLOCK_DIVISOR == 32
        {
            CMT0.CMCR.BIT.CKS = 1;
        }
    #elif portCLOCK_DIVISOR == 8
        {
            CMT0.CMCR.BIT.CKS = 0;
        }
    #else  /* if portCLOCK_DIVISOR == 512 */
        {
            #error Invalid portCLOCK_DIVISOR setting
        }
    #endif /* if portCLOCK_DIVISOR == 512 */

    /* Enable the interrupt... */
    _IEN( _CMT0_CMI0 )  = 1;

    /* ...and set its priority to the application defined kernel priority. */
    _IPR( _CMT0_CMI0 )  = configKERNEL_INTERRUPT_PRIORITY;

    /* Start the timer. */
    CMT.CMSTR0.BIT.STR0 = 1;
}
/*-----------------------------------------------------------*/

#if configUSE_TICKLESS_IDLE == 1

    static void prvSleep( TickType_t xExpectedIdleTime )
    {
        /* Allow the application to define some pre-sleep processing. */
        configPRE_SLEEP_PROCESSING( xExpectedIdleTime );

        /* xExpectedIdleTime being set to 0 by configPRE_SLEEP_PROCESSING()
         * means the application defined code has already executed the WAIT
         * instruction. */
        if( xExpectedIdleTime > 0 )
        {
            __asm volatile ( "WAIT" );
        }

        /* Allow the application to define some post sleep processing. */
        configPOST_SLEEP_PROCESSING( xExpectedIdleTime );
    }

#endif /* configUSE_TICKLESS_IDLE */
/*-----------------------------------------------------------*/

#if configUSE_TICKLESS_IDLE == 1

    void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
    {
        uint32_t         ulMatchValue, ulCompleteTickPeriods, ulCurrentCount;
        eSleepModeStatus eSleepAction;

        /* THIS FUNCTION IS CALLED WITH THE SCHEDULER SUSPENDED. */

        /* Make sure the CMT reload value does not overflow the counter. */
        if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
        {
            xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
        }

        /* Calculate the reload value required to wait xExpectedIdleTime tick
         * periods. */
        ulMatchValue        = ulMatchValueForOneTick * xExpectedIdleTime;

        if( ulMatchValue > ulStoppedTimerCompensation )
        {
            /* Compensate for the fact that the CMT is going to be stopped
             * momentarily. */
            ulMatchValue -= ulStoppedTimerCompensation;
        }

        /* Stop the CMT momentarily.  The time the CMT 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. */
        CMT.CMSTR0.BIT.STR0 = 0;

        while( CMT.CMSTR0.BIT.STR0 == 1 )
        {
            /* Nothing to do here. */
        }

        /* Critical section using the global interrupt bit as the i bit is
         * automatically reset by the WAIT instruction. */
        __asm volatile ( "CLRPSW i" );

        /* The tick flag is set to false before sleeping.  If it is true when
         * sleep mode is exited then sleep mode was probably exited because the
         * tick was suppressed for the entire xExpectedIdleTime period. */
        ulTickFlag          = pdFALSE;

        /* If a context switch is pending then abandon the low power entry as
         * the context switch might have been pended by an external interrupt that
         * requires processing. */
        eSleepAction        = eTaskConfirmSleepModeStatus();

        if( eSleepAction == eAbortSleep )
        {
            /* Restart tick. */
            CMT.CMSTR0.BIT.STR0 = 1;
            __asm volatile ( "SETPSW i" );
        }
        else if( eSleepAction == eNoTasksWaitingTimeout )
        {
            /* Protection off. */
            SYSTEM.PRCR.WORD      = portUNLOCK_KEY;

            /* Ready for software standby with all clocks stopped. */
            SYSTEM.SBYCR.BIT.SSBY = 1;

            /* Protection on. */
            SYSTEM.PRCR.WORD      = portLOCK_KEY;

            /* Sleep until something happens.  Calling prvSleep() will
             * automatically reset the i bit in the PSW. */
            prvSleep( xExpectedIdleTime );

            /* Restart the CMT. */
            CMT.CMSTR0.BIT.STR0   = 1;
        }
        else
        {
            /* Protection off. */
            SYSTEM.PRCR.WORD           = portUNLOCK_KEY;

            /* Ready for deep sleep mode. */
            SYSTEM.MSTPCRC.BIT.DSLPE   = 1;
            SYSTEM.MSTPCRA.BIT.MSTPA28 = 1;
            SYSTEM.SBYCR.BIT.SSBY      = 0;

            /* Protection on. */
            SYSTEM.PRCR.WORD           = portLOCK_KEY;

            /* Adjust the match value to take into account that the current
             * time slice is already partially complete. */
            ulMatchValue              -= ( uint32_t ) CMT0.CMCNT;
            CMT0.CMCOR                 = ( uint16_t ) ulMatchValue;

            /* Restart the CMT to count up to the new match value. */
            CMT0.CMCNT                 = 0;
            CMT.CMSTR0.BIT.STR0        = 1;

            /* Sleep until something happens.  Calling prvSleep() will
             * automatically reset the i bit in the PSW. */
            prvSleep( xExpectedIdleTime );

            /* Stop CMT.  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. */
            CMT.CMSTR0.BIT.STR0        = 0;

            while( CMT.CMSTR0.BIT.STR0 == 1 )
            {
                /* Nothing to do here. */
            }

            ulCurrentCount             = ( uint32_t ) CMT0.CMCNT;

            if( ulTickFlag != pdFALSE )
            {
                /* The tick interrupt has already executed, although because
                 * this function is called with the scheduler suspended the actual
                 * tick processing will not occur until after this function has
                 * exited.  Reset the match value with whatever remains of this
                 * tick period. */
                ulMatchValue          = ulMatchValueForOneTick - ulCurrentCount;
                CMT0.CMCOR            = ( uint16_t ) ulMatchValue;

                /* The tick interrupt handler will already have pended the tick
                 * processing in the kernel.  As the pending tick will be
                 * processed as soon as this function exits, the tick value
                 * maintained by the tick is stepped forward by one less than the
                 * time spent sleeping.  The actual stepping of the tick appears
                 * later in this function. */
                ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
            }
            else
            {
                /* Something other than the tick interrupt ended the sleep.
                 * How	many complete tick periods passed while the processor was
                 * sleeping? */
                ulCompleteTickPeriods = ulCurrentCount / ulMatchValueForOneTick;

                /* The match value is set to whatever fraction of a single tick
                 * period remains. */
                ulMatchValue          = ulCurrentCount - ( ulCompleteTickPeriods * ulMatchValueForOneTick );
                CMT0.CMCOR            = ( uint16_t ) ulMatchValue;
            }

            /* Restart the CMT so it runs up to the match value.  The match value
             * will get set to the value required to generate exactly one tick period
             * the next time the CMT interrupt executes. */
            CMT0.CMCNT                 = 0;
            CMT.CMSTR0.BIT.STR0        = 1;

            /* Wind the tick forward by the number of tick periods that the CPU
             * remained in a low power state. */
            vTaskStepTick( ulCompleteTickPeriods );
        }
    }

#endif /* configUSE_TICKLESS_IDLE */