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    ***************************************************************************


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*/

/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the ARM CM4F port.
 *----------------------------------------------------------*/

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

#ifndef __VFP_FP__
	#error This port can only be used when the project options are configured to enable hardware floating point support.
#endif

#ifndef configSYSTICK_CLOCK_HZ
	#define configSYSTICK_CLOCK_HZ configCPU_CLOCK_HZ
#endif

/* Constants required to manipulate the core.  Registers first... */
#define portNVIC_SYSTICK_CTRL_REG			( * ( ( volatile unsigned long * ) 0xe000e010 ) )
#define portNVIC_SYSTICK_LOAD_REG			( * ( ( volatile unsigned long * ) 0xe000e014 ) )
#define portNVIC_SYSTICK_CURRENT_VALUE_REG	( * ( ( volatile unsigned long * ) 0xe000e018 ) )
#define portNVIC_INT_CTRL_REG				( * ( ( volatile unsigned long * ) 0xe000ed04 ) )
#define portNVIC_SYSPRI2_REG				( * ( ( volatile unsigned long * ) 0xe000ed20 ) )
/* ...then bits in the registers. */
#define portNVIC_SYSTICK_CLK_BIT			( 1UL << 2UL )
#define portNVIC_SYSTICK_INT_BIT			( 1UL << 1UL )
#define portNVIC_SYSTICK_ENABLE_BIT			( 1UL << 0UL )
#define portNVIC_SYSTICK_COUNT_FLAG_BIT		( 1UL << 16UL )
#define portNVIC_PENDSVSET_BIT				( 1UL << 28UL )
#define portNVIC_PENDSVCLEAR_BIT 			( 1UL << 27UL )
#define portNVIC_PEND_SYSTICK_CLEAR_BIT		( 1UL << 25UL )

#define portNVIC_PENDSV_PRI				( ( ( unsigned long ) configKERNEL_INTERRUPT_PRIORITY ) << 16UL )
#define portNVIC_SYSTICK_PRI			( ( ( unsigned long ) configKERNEL_INTERRUPT_PRIORITY ) << 24UL )

/* Constants required to manipulate the VFP. */
#define portFPCCR					( ( volatile unsigned long * ) 0xe000ef34 ) /* Floating point context control register. */
#define portASPEN_AND_LSPEN_BITS	( 0x3UL << 30UL )

/* Constants required to set up the initial stack. */
#define portINITIAL_XPSR			( 0x01000000 )
#define portINITIAL_EXEC_RETURN		( 0xfffffffd )

/* The priority used by the kernel is assigned to a variable to make access
from inline assembler easier. */
const unsigned long ulKernelPriority = configKERNEL_INTERRUPT_PRIORITY;

/* Each task maintains its own interrupt status in the critical nesting
variable. */
static unsigned portBASE_TYPE 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 ) __attribute__ (( naked ));
void xPortSysTickHandler( void );
void vPortSVCHandler( void ) __attribute__ (( naked ));

/*
 * Start first task is a separate function so it can be tested in isolation.
 */
static void prvPortStartFirstTask( void ) __attribute__ (( naked ));

/*
 * Function to enable the VFP.
 */
 static void vPortEnableVFP( void ) __attribute__ (( naked ));

/*-----------------------------------------------------------*/

/*
 * The number of SysTick increments that make up one tick period.
 */
#if configUSE_TICKLESS_IDLE == 1
	static unsigned long ulTimerReloadValueForOneTick = 0;
#endif

/*
 * 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 unsigned long 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 unsigned long ulStoppedTimerCompensation = 0;
#endif /* configUSE_TICKLESS_IDLE */

/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
{
	/* Simulate the stack frame as it would be created by a context switch
	interrupt. */

	/* Offset added to account for the way the MCU uses the stack on entry/exit
	of interrupts, and to ensure alignment. */
	pxTopOfStack--;

	*pxTopOfStack = portINITIAL_XPSR;	/* xPSR */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) pxCode;	/* PC */
	pxTopOfStack--;
	*pxTopOfStack = 0;	/* LR */

	/* Save code space by skipping register initialisation. */
	pxTopOfStack -= 5;	/* R12, R3, R2 and R1. */
	*pxTopOfStack = ( portSTACK_TYPE ) pvParameters;	/* R0 */

	/* A save method is being used that requires each task to maintain its
	own exec return value. */
	pxTopOfStack--;
	*pxTopOfStack = portINITIAL_EXEC_RETURN;

	pxTopOfStack -= 8;	/* R11, R10, R9, R8, R7, R6, R5 and R4. */

	return pxTopOfStack;
}
/*-----------------------------------------------------------*/

void vPortSVCHandler( void )
{
	__asm volatile (
					"	ldr	r3, pxCurrentTCBConst2		\n" /* Restore the context. */
					"	ldr r1, [r3]					\n" /* Use pxCurrentTCBConst to get the pxCurrentTCB address. */
					"	ldr r0, [r1]					\n" /* The first item in pxCurrentTCB is the task top of stack. */
					"	ldmia r0!, {r4-r11, r14}		\n" /* Pop the registers that are not automatically saved on exception entry and the critical nesting count. */
					"	msr psp, r0						\n" /* Restore the task stack pointer. */
					"	mov r0, #0 						\n"
					"	msr	basepri, r0					\n"
					"	bx r14							\n"
					"									\n"
					"	.align 2						\n"
					"pxCurrentTCBConst2: .word pxCurrentTCB				\n"
				);
}
/*-----------------------------------------------------------*/

static void prvPortStartFirstTask( void )
{
	__asm volatile(
					" ldr r0, =0xE000ED08 	\n" /* Use the NVIC offset register to locate the stack. */
					" ldr r0, [r0] 			\n"
					" ldr r0, [r0] 			\n"
					" msr msp, r0			\n" /* Set the msp back to the start of the stack. */
					" cpsie i				\n" /* Globally enable interrupts. */
					" svc 0					\n" /* System call to start first task. */
					" nop					\n"
				);
}
/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
portBASE_TYPE xPortStartScheduler( void )
{
	/* configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to 0.
	See http://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html */
	configASSERT( configMAX_SYSCALL_INTERRUPT_PRIORITY );

	/* Make PendSV, CallSV and SysTick the same priroity as the kernel. */
	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;

	/* Ensure the VFP is enabled - it should be anyway. */
	vPortEnableVFP();

	/* Lazy save always. */
	*( portFPCCR ) |= portASPEN_AND_LSPEN_BITS;

	/* Start the first task. */
	prvPortStartFirstTask();

	/* Should not get here! */
	return 0;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
	/* It is unlikely that the CM4F port will require this function as there
	is nothing to return to.  */
}
/*-----------------------------------------------------------*/

void vPortYieldFromISR( void )
{
	/* Set a PendSV to request a context switch. */
	portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;
}
/*-----------------------------------------------------------*/

void vPortEnterCritical( void )
{
	portDISABLE_INTERRUPTS();
	uxCriticalNesting++;
}
/*-----------------------------------------------------------*/

void vPortExitCritical( void )
{
	uxCriticalNesting--;
	if( uxCriticalNesting == 0 )
	{
		portENABLE_INTERRUPTS();
	}
}
/*-----------------------------------------------------------*/

__attribute__(( naked )) unsigned long ulPortSetInterruptMask( void )
{
	__asm volatile														\
	(																	\
		"	mrs r0, basepri											\n" \
		"	mov r1, %0												\n"	\
		"	msr basepri, r1											\n" \
		"	bx lr													\n" \
		:: "i" ( configMAX_SYSCALL_INTERRUPT_PRIORITY ) : "r0", "r1"	\
	);

	/* This return will not be reached but is necessary to prevent compiler
	warnings. */
	return 0;
}
/*-----------------------------------------------------------*/

__attribute__(( naked )) void vPortClearInterruptMask( unsigned long ulNewMaskValue )
{
	__asm volatile													\
	(																\
		"	msr basepri, r0										\n"	\
		"	bx lr												\n" \
		:::"r0"														\
	);

	/* Just to avoid compiler warnings. */
	( void ) ulNewMaskValue;
}
/*-----------------------------------------------------------*/

void xPortPendSVHandler( void )
{
	/* This is a naked function. */

	__asm volatile
	(
	"	mrs r0, psp							\n"
	"										\n"
	"	ldr	r3, pxCurrentTCBConst				\n" /* Get the location of the current TCB. */
	"	ldr	r2, [r3]						\n"
	"										\n"
	"	tst r14, #0x10						\n" /* Is the task using the FPU context?  If so, push high vfp registers. */
	"	it eq								\n"
	"	vstmdbeq r0!, {s16-s31}				\n"
	"										\n"
	"	stmdb r0!, {r4-r11, r14}			\n" /* Save the core registers. */
	"										\n"
	"	str r0, [r2]						\n" /* Save the new top of stack into the first member of the TCB. */
	"										\n"
	"	stmdb sp!, {r3, r14}				\n"
	"	mov r0, %0 							\n"
	"	msr basepri, r0						\n"
	"	bl vTaskSwitchContext				\n"
	"	mov r0, #0							\n"
	"	msr basepri, r0						\n"
	"	ldmia sp!, {r3, r14}				\n"
	"										\n"
	"	ldr r1, [r3]						\n" /* The first item in pxCurrentTCB is the task top of stack. */
	"	ldr r0, [r1]						\n"
	"										\n"
	"	ldmia r0!, {r4-r11, r14}			\n" /* Pop the core registers. */
	"										\n"
	"	tst r14, #0x10						\n" /* Is the task using the FPU context?  If so, pop the high vfp registers too. */
	"	it eq								\n"
	"	vldmiaeq r0!, {s16-s31}				\n"
	"										\n"
	"	msr psp, r0							\n"
	"	bx r14								\n"
	"										\n"
	"	.align 2							\n"
	"pxCurrentTCBConst: .word pxCurrentTCB	\n"
	::"i"(configMAX_SYSCALL_INTERRUPT_PRIORITY)
	);
}
/*-----------------------------------------------------------*/

void xPortSysTickHandler( void )
{
	/* If using preemption, also force a context switch. */
	#if configUSE_PREEMPTION == 1
		portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;
	#endif

	/* Only reset the systick load register if configUSE_TICKLESS_IDLE is set to
	1.  If it is set to 0 tickless idle is not being used.  If it is set to a
	value other than 0 or 1 then a timer other than the SysTick is being used
	to generate the tick interrupt. */
	#if configUSE_TICKLESS_IDLE == 1
		portNVIC_SYSTICK_LOAD_REG = ulTimerReloadValueForOneTick;
	#endif

	( void ) portSET_INTERRUPT_MASK_FROM_ISR();
	{
		vTaskIncrementTick();
	}
	portCLEAR_INTERRUPT_MASK_FROM_ISR( 0 );
}
/*-----------------------------------------------------------*/

#if configUSE_TICKLESS_IDLE == 1

	__attribute__((weak)) void vPortSuppressTicksAndSleep( portTickType xExpectedIdleTime )
	{
	unsigned long ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickIncrements;
	portTickType xModifiableIdleTime;

		/* Make sure the SysTick reload value does not overflow the counter. */
		if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
		{
			xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
		}

		/* 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, and the fraction of a tick period is
		accounted for later. */
		ulReloadValue = ( ulTimerReloadValueForOneTick * ( xExpectedIdleTime - 1UL ) );
		if( ulReloadValue > ulStoppedTimerCompensation )
		{
			ulReloadValue -= ulStoppedTimerCompensation;
		}

		/* 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 | portNVIC_SYSTICK_INT_BIT;

		/* Adjust the reload value to take into account that the current time
		slice is already partially complete. */
		ulReloadValue += ( portNVIC_SYSTICK_LOAD_REG - ( portNVIC_SYSTICK_LOAD_REG - portNVIC_SYSTICK_CURRENT_VALUE_REG ) );

		/* 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" );

		/* 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 SysTick. */
			portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;

			/* Re-enable interrupts - see comments above the cpsid instruction()
			above. */
			__asm volatile( "cpsie i" );
		}
		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_CLK_BIT | portNVIC_SYSTICK_INT_BIT | 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( "wfi" );
			}
			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. */
			portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT;

			/* Re-enable interrupts - see comments above the cpsid instruction()
			above. */
			__asm volatile( "cpsie i" );

			if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
			{
				/* The tick interrupt has already executed, and the SysTick
				count reloaded with the portNVIC_SYSTICK_LOAD_REG value.
				Reset the portNVIC_SYSTICK_LOAD_REG with whatever remains of
				this tick period. */
				portNVIC_SYSTICK_LOAD_REG = ulTimerReloadValueForOneTick - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );

				/* 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. */
				ulCompletedSysTickIncrements = ( xExpectedIdleTime * ulTimerReloadValueForOneTick ) - portNVIC_SYSTICK_CURRENT_VALUE_REG;

				/* How many complete tick periods passed while the processor
				was waiting? */
				ulCompleteTickPeriods = ulCompletedSysTickIncrements / ulTimerReloadValueForOneTick;

				/* The reload value is set to whatever fraction of a single tick
				period remains. */
				portNVIC_SYSTICK_LOAD_REG = ( ( ulCompleteTickPeriods + 1 ) * ulTimerReloadValueForOneTick ) - ulCompletedSysTickIncrements;
			}

			/* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG
			again, then set portNVIC_SYSTICK_LOAD_REG back to its standard
			value. */
			portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
			portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;

			vTaskStepTick( ulCompleteTickPeriods );
		}
	}

#endif /* #if configUSE_TICKLESS_IDLE */
/*-----------------------------------------------------------*/

/*
 * Setup the systick timer to generate the tick interrupts at the required
 * frequency.
 */
__attribute__(( weak )) void vPortSetupTimerInterrupt( void )
{
	/* Calculate the constants required to configure the tick interrupt. */
	#if configUSE_TICKLESS_IDLE == 1
	{
		ulTimerReloadValueForOneTick = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
		xMaximumPossibleSuppressedTicks = 0xffffffUL / ( ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL );
		ulStoppedTimerCompensation = 45UL / ( 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;
}
/*-----------------------------------------------------------*/

/* This is a naked function. */
static void vPortEnableVFP( void )
{
	__asm volatile
	(
		"	ldr.w r0, =0xE000ED88		\n" /* The FPU enable bits are in the CPACR. */
		"	ldr r1, [r0]				\n"
		"								\n"
		"	orr r1, r1, #( 0xf << 20 )	\n" /* Enable CP10 and CP11 coprocessors, then save back. */
		"	str r1, [r0]				\n"
		"	bx r14						"
	);
}