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    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
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    ***************************************************************************
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*/

/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the Atmel ARM7 port.
 *----------------------------------------------------------*/


/* Standard includes. */
#include <stdlib.h>

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

/* Constants required to setup the initial stack. */
#define portINITIAL_SPSR				( ( StackType_t ) 0x1f ) /* System mode, ARM mode, interrupts enabled. */
#define portTHUMB_MODE_BIT				( ( StackType_t ) 0x20 )
#define portINSTRUCTION_SIZE			( ( StackType_t ) 4 )

/* Constants required to setup the PIT. */
#define portPIT_CLOCK_DIVISOR			( ( uint32_t ) 16 )
#define portPIT_COUNTER_VALUE			( ( ( configCPU_CLOCK_HZ / portPIT_CLOCK_DIVISOR ) / 1000UL ) * portTICK_PERIOD_MS )

/* Constants required to handle critical sections. */
#define portNO_CRITICAL_NESTING 		( ( uint32_t ) 0 )


#define portINT_LEVEL_SENSITIVE  0
#define portPIT_ENABLE      	( ( uint16_t ) 0x1 << 24 )
#define portPIT_INT_ENABLE     	( ( uint16_t ) 0x1 << 25 )
/*-----------------------------------------------------------*/

/* Setup the PIT to generate the tick interrupts. */
static void prvSetupTimerInterrupt( void );

/* ulCriticalNesting will get set to zero when the first task starts.  It
cannot be initialised to 0 as this will cause interrupts to be enabled
during the kernel initialisation process. */
uint32_t ulCriticalNesting = ( uint32_t ) 9999;

/*-----------------------------------------------------------*/

/*
 * Initialise the stack of a task to look exactly as if a call to
 * portSAVE_CONTEXT had been called.
 *
 * See header file for description.
 */
StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )
{
StackType_t *pxOriginalTOS;

	pxOriginalTOS = pxTopOfStack;

	/* To ensure asserts in tasks.c don't fail, although in this case the assert
	is not really required. */
	pxTopOfStack--;

	/* Setup the initial stack of the task.  The stack is set exactly as
	expected by the portRESTORE_CONTEXT() macro. */

	/* First on the stack is the return address - which in this case is the
	start of the task.  The offset is added to make the return address appear
	as it would within an IRQ ISR. */
	*pxTopOfStack = ( StackType_t ) pxCode + portINSTRUCTION_SIZE;		
	pxTopOfStack--;

	*pxTopOfStack = ( StackType_t ) 0xaaaaaaaa;	/* R14 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) pxOriginalTOS; /* Stack used when task starts goes in R13. */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) 0x12121212;	/* R12 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x11111111;	/* R11 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x10101010;	/* R10 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x09090909;	/* R9 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x08080808;	/* R8 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x07070707;	/* R7 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x06060606;	/* R6 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x05050505;	/* R5 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x04040404;	/* R4 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x03030303;	/* R3 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x02020202;	/* R2 */
	pxTopOfStack--;	
	*pxTopOfStack = ( StackType_t ) 0x01010101;	/* R1 */
	pxTopOfStack--;	

	/* When the task starts is will expect to find the function parameter in
	R0. */
	*pxTopOfStack = ( StackType_t ) pvParameters; /* R0 */
	pxTopOfStack--;

	/* The status register is set for system mode, with interrupts enabled. */
	*pxTopOfStack = ( StackType_t ) portINITIAL_SPSR;
	
	if( ( ( uint32_t ) pxCode & 0x01UL ) != 0x00UL )
	{
		/* We want the task to start in thumb mode. */
		*pxTopOfStack |= portTHUMB_MODE_BIT;
	}	
	
	pxTopOfStack--;

	/* Interrupt flags cannot always be stored on the stack and will
	instead be stored in a variable, which is then saved as part of the
	tasks context. */
	*pxTopOfStack = portNO_CRITICAL_NESTING;

	return pxTopOfStack;	
}
/*-----------------------------------------------------------*/

BaseType_t xPortStartScheduler( void )
{
extern void vPortStartFirstTask( void );

	/* Start the timer that generates the tick ISR.  Interrupts are disabled
	here already. */
	prvSetupTimerInterrupt();

	/* Start the first task. */
	vPortStartFirstTask();	

	/* Should not get here! */
	return 0;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
	/* It is unlikely that the ARM port will require this function as there
	is nothing to return to.  */
}
/*-----------------------------------------------------------*/

#if configUSE_PREEMPTION == 0

	/* The cooperative scheduler requires a normal IRQ service routine to
	simply increment the system tick. */
	static __arm __irq void vPortNonPreemptiveTick( void );
	static __arm __irq void vPortNonPreemptiveTick( void )
	{
		uint32_t ulDummy;
		
		/* Increment the tick count - which may wake some tasks but as the
		preemptive scheduler is not being used any woken task is not given
		processor time no matter what its priority. */
		xTaskIncrementTick();
		
		/* Clear the PIT interrupt. */
		ulDummy = AT91C_BASE_PITC->PITC_PIVR;
		
		/* End the interrupt in the AIC. */
		AT91C_BASE_AIC->AIC_EOICR = ulDummy;
	}

#else

	/* Currently the IAR port requires the preemptive tick function to be
	defined in an asm file. */

#endif

/*-----------------------------------------------------------*/

static void prvSetupTimerInterrupt( void )
{
AT91PS_PITC pxPIT = AT91C_BASE_PITC;

	/* Setup the AIC for PIT interrupts.  The interrupt routine chosen depends
	on whether the preemptive or cooperative scheduler is being used. */
	#if configUSE_PREEMPTION == 0

		AT91F_AIC_ConfigureIt( AT91C_BASE_AIC, AT91C_ID_SYS, AT91C_AIC_PRIOR_HIGHEST, portINT_LEVEL_SENSITIVE, ( void (*)(void) ) vPortNonPreemptiveTick );

	#else
		
		extern void ( vPortPreemptiveTick )( void );
		AT91F_AIC_ConfigureIt( AT91C_BASE_AIC, AT91C_ID_SYS, AT91C_AIC_PRIOR_HIGHEST, portINT_LEVEL_SENSITIVE, ( void (*)(void) ) vPortPreemptiveTick );

	#endif

	/* Configure the PIT period. */
	pxPIT->PITC_PIMR = portPIT_ENABLE | portPIT_INT_ENABLE | portPIT_COUNTER_VALUE;

	/* Enable the interrupt.  Global interrupts are disables at this point so
	this is safe. */
	AT91F_AIC_EnableIt( AT91C_BASE_AIC, AT91C_ID_SYS );
}
/*-----------------------------------------------------------*/

void vPortEnterCritical( void )
{
	/* Disable interrupts first! */
	__disable_interrupt();

	/* Now interrupts are disabled ulCriticalNesting can be accessed
	directly.  Increment ulCriticalNesting to keep a count of how many times
	portENTER_CRITICAL() has been called. */
	ulCriticalNesting++;
}
/*-----------------------------------------------------------*/

void vPortExitCritical( void )
{
	if( ulCriticalNesting > portNO_CRITICAL_NESTING )
	{
		/* Decrement the nesting count as we are leaving a critical section. */
		ulCriticalNesting--;

		/* If the nesting level has reached zero then interrupts should be
		re-enabled. */
		if( ulCriticalNesting == portNO_CRITICAL_NESTING )
		{
			__enable_interrupt();
		}
	}
}
/*-----------------------------------------------------------*/