text: /*
      FreeRTOS V9.0.0 - Copyright (C) 2016 Real Time Engineers Ltd.
      All rights reserved
  
      VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.
  
      This file is part of the FreeRTOS distribution.
  
      FreeRTOS is free software; you can redistribute it and/or modify it under
      the terms of the GNU General Public License (version 2) as published by the
      Free Software Foundation >>>> AND MODIFIED BY <<<< the FreeRTOS exception.
  
      ***************************************************************************
      >>!   NOTE: The modification to the GPL is included to allow you to     !<<
      >>!   distribute a combined work that includes FreeRTOS without being   !<<
      >>!   obliged to provide the source code for proprietary components     !<<
      >>!   outside of the FreeRTOS kernel.                                   !<<
      ***************************************************************************
  
      FreeRTOS is distributed in the hope that it will be useful, but WITHOUT ANY
      WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
      FOR A PARTICULAR PURPOSE.  Full license text is available on the following
      link: http://www.freertos.org/a00114.html
  
      ***************************************************************************
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      ***************************************************************************
  
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      1 tab == 4 spaces!
  */
  
  /*-----------------------------------------------------------
   * Implementation of functions defined in portable.h for the ARM CM3 port.
   *----------------------------------------------------------*/
  
  /* Scheduler includes. */
  #include "FreeRTOS.h"
  #include "task.h"
  
  #ifndef configKERNEL_INTERRUPT_PRIORITY
  	#define configKERNEL_INTERRUPT_PRIORITY 255
  #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
  
  /* The __weak attribute does not work as you might expect with the Keil tools
  so the configOVERRIDE_DEFAULT_TICK_CONFIGURATION constant must be set to 1 if
  the application writer wants to provide their own implementation of
  vPortSetupTimerInterrupt().  Ensure configOVERRIDE_DEFAULT_TICK_CONFIGURATION
  is defined. */
  #ifndef configOVERRIDE_DEFAULT_TICK_CONFIGURATION
  	#define configOVERRIDE_DEFAULT_TICK_CONFIGURATION 0
  #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_SYSPRI2_REG				( * ( ( volatile uint32_t * ) 0xe000ed20 ) )
  /* ...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 )
  
  /* Masks off all bits but the VECTACTIVE bits in the ICSR register. */
  #define portVECTACTIVE_MASK					( 0xFFUL )
  
  #define portNVIC_PENDSV_PRI					( ( ( uint32_t ) configKERNEL_INTERRUPT_PRIORITY ) << 16UL )
  #define portNVIC_SYSTICK_PRI				( ( ( uint32_t ) configKERNEL_INTERRUPT_PRIORITY ) << 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 )
  
  /* Constants required to set up the initial stack. */
  #define portINITIAL_XPSR			( 0x01000000 )
  
  /* 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 )
  
  /* Each task maintains its own interrupt status in the critical nesting
  variable. */
  static UBaseType_t uxCriticalNesting = 0xaaaaaaaa;
  
  /*
   * 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 xPortPendSVHandler( void );
  void xPortSysTickHandler( void );
  void vPortSVCHandler( void );
  
  /*
   * Start first task is a separate function so it can be tested in isolation.
   */
  static void prvStartFirstTask( void );
  
  /*
   * Used to catch tasks that attempt to return from their implementing function.
   */
  static void prvTaskExitError( void );
  
  /*-----------------------------------------------------------*/
  
  /*
   * The number of SysTick increments that make up one tick period.
   */
  #if configUSE_TICKLESS_IDLE == 1
  	static uint32_t ulTimerCountsForOneTick = 0;
  #endif /* configUSE_TICKLESS_IDLE */
  
  /*
   * The maximum number of tick periods that can be suppressed is limited by the
   * 24 bit resolution of the SysTick timer.
   */
  #if configUSE_TICKLESS_IDLE == 1
  	static uint32_t xMaximumPossibleSuppressedTicks = 0;
  #endif /* configUSE_TICKLESS_IDLE */
  
  /*
   * Compensate for the CPU cycles that pass while the SysTick is stopped (low
   * power functionality only.
   */
  #if configUSE_TICKLESS_IDLE == 1
  	static uint32_t ulStoppedTimerCompensation = 0;
  #endif /* configUSE_TICKLESS_IDLE */
  
  /*
   * 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 = ( uint8_t * ) portNVIC_IP_REGISTERS_OFFSET_16;
  #endif /* configASSERT_DEFINED */
  
  /*-----------------------------------------------------------*/
  
  /*
   * See header file for description.
   */
  StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )
  {
  	/* Simulate the stack frame as it would be created by a context switch
  	interrupt. */
  	pxTopOfStack--; /* Offset added to account for the way the MCU uses the stack on entry/exit of interrupts. */
  	*pxTopOfStack = portINITIAL_XPSR;	/* xPSR */
  	pxTopOfStack--;
  	*pxTopOfStack = ( ( StackType_t ) pxCode ) & portSTART_ADDRESS_MASK;	/* PC */
  	pxTopOfStack--;
  	*pxTopOfStack = ( StackType_t ) prvTaskExitError;	/* LR */
  
  	pxTopOfStack -= 5;	/* R12, R3, R2 and R1. */
  	*pxTopOfStack = ( StackType_t ) pvParameters;	/* R0 */
  	pxTopOfStack -= 8;	/* R11, R10, R9, R8, R7, R6, R5 and R4. */
  
  	return pxTopOfStack;
  }
  /*-----------------------------------------------------------*/
  
  static void prvTaskExitError( void )
  {
  	/* 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( uxCriticalNesting == ~0UL );
  	portDISABLE_INTERRUPTS();
  	for( ;; );
  }
  /*-----------------------------------------------------------*/
  
  __asm void vPortSVCHandler( void )
  {
  	PRESERVE8
  
  	ldr	r3, =pxCurrentTCB	/* Restore the context. */
  	ldr r1, [r3]			/* Use pxCurrentTCBConst to get the pxCurrentTCB address. */
  	ldr r0, [r1]			/* The first item in pxCurrentTCB is the task top of stack. */
  	ldmia r0!, {r4-r11}		/* Pop the registers that are not automatically saved on exception entry and the critical nesting count. */
  	msr psp, r0				/* Restore the task stack pointer. */
  	isb
  	mov r0, #0
  	msr	basepri, r0
  	orr r14, #0xd
  	bx r14
  }
  /*-----------------------------------------------------------*/
  
  __asm void prvStartFirstTask( void )
  {
  	PRESERVE8
  
  	/* Use the NVIC offset register to locate the stack. */
  	ldr r0, =0xE000ED08
  	ldr r0, [r0]
  	ldr r0, [r0]
  
  	/* Set the msp back to the start of the stack. */
  	msr msp, r0
  	/* Globally enable interrupts. */
  	cpsie i
  	cpsie f
  	dsb
  	isb
  	/* Call SVC to start the first task. */
  	svc 0
  	nop
  	nop
  }
  /*-----------------------------------------------------------*/
  
  /*
   * See header file for description.
   */
  BaseType_t xPortStartScheduler( void )
  {
  	#if( configASSERT_DEFINED == 1 )
  	{
  		volatile uint32_t ulOriginalPriority;
  		volatile uint8_t * const pucFirstUserPriorityRegister = ( uint8_t * ) ( portNVIC_IP_REGISTERS_OFFSET_16 + portFIRST_USER_INTERRUPT_NUMBER );
  		volatile uint8_t ucMaxPriorityValue;
  
  		/* Determine the maximum priority from which ISR safe FreeRTOS API
  		functions can be called.  ISR safe functions are those that end in
  		"FromISR".  FreeRTOS maintains separate thread and ISR API functions to
  		ensure interrupt entry is as fast and simple as possible.
  
  		Save the interrupt priority value that is about to be clobbered. */
  		ulOriginalPriority = *pucFirstUserPriorityRegister;
  
  		/* Determine the number of priority bits available.  First write to all
  		possible bits. */
  		*pucFirstUserPriorityRegister = portMAX_8_BIT_VALUE;
  
  		/* Read the value back to see how many bits stuck. */
  		ucMaxPriorityValue = *pucFirstUserPriorityRegister;
  
  		/* Use the same mask on the maximum system call priority. */
  		ucMaxSysCallPriority = configMAX_SYSCALL_INTERRUPT_PRIORITY & ucMaxPriorityValue;
  
  		/* Calculate the maximum acceptable priority group value for the number
  		of bits read back. */
  		ulMaxPRIGROUPValue = portMAX_PRIGROUP_BITS;
  		while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
  		{
  			ulMaxPRIGROUPValue--;
  			ucMaxPriorityValue <<= ( uint8_t ) 0x01;
  		}
  
  		/* Shift the priority group value back to its position within the AIRCR
  		register. */
  		ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
  		ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
  
  		/* Restore the clobbered interrupt priority register to its original
  		value. */
  		*pucFirstUserPriorityRegister = ulOriginalPriority;
  	}
  	#endif /* conifgASSERT_DEFINED */
  
  	/* Make PendSV and SysTick the lowest priority interrupts. */
  	portNVIC_SYSPRI2_REG |= portNVIC_PENDSV_PRI;
  	portNVIC_SYSPRI2_REG |= portNVIC_SYSTICK_PRI;
  
  	/* Start the timer that generates the tick ISR.  Interrupts are disabled
  	here already. */
  	vPortSetupTimerInterrupt();
  
  	/* Initialise the critical nesting count ready for the first task. */
  	uxCriticalNesting = 0;
  
  	/* Start the first task. */
  	prvStartFirstTask();
  
  	/* 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 )
  {
  	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 );
  	}
  }
  /*-----------------------------------------------------------*/
  
  void vPortExitCritical( void )
  {
  	configASSERT( uxCriticalNesting );
  	uxCriticalNesting--;
  	if( uxCriticalNesting == 0 )
  	{
  		portENABLE_INTERRUPTS();
  	}
  }
  /*-----------------------------------------------------------*/
  
  __asm void xPortPendSVHandler( void )
  {
  	extern uxCriticalNesting;
  	extern pxCurrentTCB;
  	extern vTaskSwitchContext;
  
  	PRESERVE8
  
  	mrs r0, psp
  	isb
  
  	ldr	r3, =pxCurrentTCB		/* Get the location of the current TCB. */
  	ldr	r2, [r3]
  
  	stmdb r0!, {r4-r11}			/* Save the remaining registers. */
  	str r0, [r2]				/* Save the new top of stack into the first member of the TCB. */
  
  	stmdb sp!, {r3, r14}
  	mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITY
  	msr basepri, r0
  	dsb
  	isb
  	bl vTaskSwitchContext
  	mov r0, #0
  	msr basepri, r0
  	ldmia sp!, {r3, r14}
  
  	ldr r1, [r3]
  	ldr r0, [r1]				/* The first item in pxCurrentTCB is the task top of stack. */
  	ldmia r0!, {r4-r11}			/* Pop the registers and the critical nesting count. */
  	msr psp, r0
  	isb
  	bx r14
  	nop
  }
  /*-----------------------------------------------------------*/
  
  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 - therefore the slightly faster vPortRaiseBASEPRI() function is used
  	in place of portSET_INTERRUPT_MASK_FROM_ISR(). */
  	vPortRaiseBASEPRI();
  	{
  		/* 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;
  		}
  	}
  	vPortClearBASEPRIFromISR();
  }
  /*-----------------------------------------------------------*/
  
  #if configUSE_TICKLESS_IDLE == 1
  
  	__weak void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
  	{
  	uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements, ulSysTickCTRL;
  	TickType_t xModifiableIdleTime;
  
  		/* Make sure the SysTick reload value does not overflow the counter. */
  		if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
  		{
  			xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
  		}
  
  		/* 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_ENABLE_BIT;
  
  		/* Calculate the reload value required to wait xExpectedIdleTime
  		tick periods.  -1 is used because this code will execute part way
  		through one of the tick periods. */
  		ulReloadValue = portNVIC_SYSTICK_CURRENT_VALUE_REG + ( ulTimerCountsForOneTick * ( xExpectedIdleTime - 1UL ) );
  		if( ulReloadValue > ulStoppedTimerCompensation )
  		{
  			ulReloadValue -= ulStoppedTimerCompensation;
  		}
  
  		/* Enter a critical section but don't use the taskENTER_CRITICAL()
  		method as that will mask interrupts that should exit sleep mode. */
  		__disable_irq();
  		__dsb( portSY_FULL_READ_WRITE );
  		__isb( portSY_FULL_READ_WRITE );
  
  		/* 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 )
  		{
  			/* Restart from whatever is left in the count register to complete
  			this tick period. */
  			portNVIC_SYSTICK_LOAD_REG = portNVIC_SYSTICK_CURRENT_VALUE_REG;
  
  			/* Restart SysTick. */
  			portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
  
  			/* Reset the reload register to the value required for normal tick
  			periods. */
  			portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
  
  			/* Re-enable interrupts - see comments above __disable_irq() call
  			above. */
  			__enable_irq();
  		}
  		else
  		{
  			/* 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 )
  			{
  				__dsb( portSY_FULL_READ_WRITE );
  				__wfi();
  				__isb( portSY_FULL_READ_WRITE );
  			}
  			configPOST_SLEEP_PROCESSING( xExpectedIdleTime );
  
  			/* Stop SysTick.  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. */
  			ulSysTickCTRL = portNVIC_SYSTICK_CTRL_REG;
  			portNVIC_SYSTICK_CTRL_REG = ( ulSysTickCTRL & ~portNVIC_SYSTICK_ENABLE_BIT );
  
  			/* Re-enable interrupts - see comments above __disable_irq() call
  			above. */
  			__enable_irq();
  
  			if( ( ulSysTickCTRL & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
  			{
  				uint32_t ulCalculatedLoadValue;
  
  				/* The tick interrupt has already executed, and the SysTick
  				count reloaded with ulReloadValue.  Reset the
  				portNVIC_SYSTICK_LOAD_REG with whatever remains of this 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. */
  				if( ( ulCalculatedLoadValue < ulStoppedTimerCompensation ) || ( ulCalculatedLoadValue > ulTimerCountsForOneTick ) )
  				{
  					ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL );
  				}
  
  				portNVIC_SYSTICK_LOAD_REG = ulCalculatedLoadValue;
  
  				/* 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 waiting. */
  				ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
  			}
  			else
  			{
  				/* Something other than the tick interrupt ended the sleep.
  				Work out how long the sleep lasted rounded to complete tick
  				periods (not the ulReload value which accounted for part
  				ticks). */
  				ulCompletedSysTickDecrements = ( xExpectedIdleTime * ulTimerCountsForOneTick ) - portNVIC_SYSTICK_CURRENT_VALUE_REG;
  
  				/* 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.  The critical section is used to ensure the tick interrupt
  			can only execute once in the case that the reload register is near
  			zero. */
  			portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
  			portENTER_CRITICAL();
  			{
  				portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
  				vTaskStepTick( ulCompleteTickPeriods );
  				portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
  			}
  			portEXIT_CRITICAL();
  		}
  	}
  
  #endif /* #if configUSE_TICKLESS_IDLE */
  
  /*-----------------------------------------------------------*/
  
  /*
   * Setup the SysTick timer to generate the tick interrupts at the required
   * frequency.
   */
  #if SysTick_Handler == 0
  
  	void vPortSetupTimerInterrupt( void )
  	{
  		/* 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 */
  
  		/* 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 );
  	}
  
  #endif /* configOVERRIDE_DEFAULT_TICK_CONFIGURATION */
  /*-----------------------------------------------------------*/
  
  __asm uint32_t vPortGetIPSR( void )
  {
  	PRESERVE8
  
  	mrs r0, ipsr
  	bx r14
  }
  /*-----------------------------------------------------------*/
  
  #if( configASSERT_DEFINED == 1 )
  
  	void vPortValidateInterruptPriority( void )
  	{
  	uint32_t ulCurrentInterrupt;
  	uint8_t ucCurrentPriority;
  
  		/* Obtain the number of the currently executing interrupt. */
  		ulCurrentInterrupt = vPortGetIPSR();
  
  		/* Is the interrupt number a user defined interrupt? */
  		if( ulCurrentInterrupt >= portFIRST_USER_INTERRUPT_NUMBER )
  		{
  			/* Look up the interrupt's priority. */
  			ucCurrentPriority = pcInterruptPriorityRegisters[ ulCurrentInterrupt ];
  
  			/* The following assertion will fail if a service routine (ISR) for
  			an interrupt that has been assigned a priority above
  			configMAX_SYSCALL_INTERRUPT_PRIORITY calls an ISR safe FreeRTOS API
  			function.  ISR safe FreeRTOS API functions must *only* be called
  			from interrupts that have been assigned a priority at or below
  			configMAX_SYSCALL_INTERRUPT_PRIORITY.
  
  			Numerically low interrupt priority numbers represent logically high
  			interrupt priorities, therefore the priority of the interrupt must
  			be set to a value equal to or numerically *higher* than
  			configMAX_SYSCALL_INTERRUPT_PRIORITY.
  
  			Interrupts that	use the FreeRTOS API must not be left at their
  			default priority of	zero as that is the highest possible priority,
  			which is guaranteed to be above configMAX_SYSCALL_INTERRUPT_PRIORITY,
  			and	therefore also guaranteed to be invalid.
  
  			FreeRTOS maintains separate thread and ISR API functions to ensure
  			interrupt entry is as fast and simple as possible.
  
  			The following links provide detailed information:
  			http://www.freertos.org/RTOS-Cortex-M3-M4.html
  			http://www.freertos.org/FAQHelp.html */
  			configASSERT( ucCurrentPriority >= ucMaxSysCallPriority );
  		}
  
  		/* Priority grouping:  The interrupt controller (NVIC) allows the bits
  		that define each interrupt's priority to be split between bits that
  		define the interrupt's pre-emption priority bits and bits that define
  		the interrupt's sub-priority.  For simplicity all bits must be defined
  		to be pre-emption priority bits.  The following assertion will fail if
  		this is not the case (if some bits represent a sub-priority).
  
  		If the application only uses CMSIS libraries for interrupt
  		configuration then the correct setting can be achieved on all Cortex-M
  		devices by calling NVIC_SetPriorityGrouping( 0 ); before starting the
  		scheduler.  Note however that some vendor specific peripheral libraries
  		assume a non-zero priority group setting, in which cases using a value
  		of zero will result in unpredicable behaviour. */
  		configASSERT( ( portAIRCR_REG & portPRIORITY_GROUP_MASK ) <= ulMaxPRIGROUPValue );
  	}
  
  #endif /* configASSERT_DEFINED */
  
  
  