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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
    Free Software Foundation >>!AND MODIFIED BY!<< the FreeRTOS exception.

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    ***************************************************************************
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*/

/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the NIOS2 port.
 *----------------------------------------------------------*/

/* Standard Includes. */
#include <string.h>
#include <errno.h>

/* Altera includes. */
#include "sys/alt_irq.h"
#include "altera_avalon_timer_regs.h"
#include "priv/alt_irq_table.h"

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

/* Interrupts are enabled. */
#define portINITIAL_ESTATUS     ( StackType_t ) 0x01 

/*-----------------------------------------------------------*/

/* 
 * Setup the timer to generate the tick interrupts.
 */
static void prvSetupTimerInterrupt( void );

/*
 * Call back for the alarm function.
 */
void vPortSysTickHandler( void * context, alt_u32 id );

/*-----------------------------------------------------------*/

static void prvReadGp( uint32_t *ulValue )
{
	asm( "stw gp, (%0)" :: "r"(ulValue) );
}
/*-----------------------------------------------------------*/

/* 
 * See header file for description. 
 */
StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )
{    
StackType_t *pxFramePointer = pxTopOfStack - 1;
StackType_t xGlobalPointer;

    prvReadGp( &xGlobalPointer ); 

    /* End of stack marker. */
    *pxTopOfStack = 0xdeadbeef;
    pxTopOfStack--;
    
    *pxTopOfStack = ( StackType_t ) pxFramePointer; 
    pxTopOfStack--;
    
    *pxTopOfStack = xGlobalPointer; 
    
    /* Space for R23 to R16. */
    pxTopOfStack -= 9;

    *pxTopOfStack = ( StackType_t ) pxCode; 
    pxTopOfStack--;

    *pxTopOfStack = portINITIAL_ESTATUS; 

    /* Space for R15 to R5. */    
    pxTopOfStack -= 12;
    
    *pxTopOfStack = ( StackType_t ) pvParameters; 

    /* Space for R3 to R1, muldiv and RA. */
    pxTopOfStack -= 5;
    
    return pxTopOfStack;
}
/*-----------------------------------------------------------*/

/* 
 * See header file for description. 
 */
BaseType_t xPortStartScheduler( void )
{
	/* Start the timer that generates the tick ISR.  Interrupts are disabled
	here already. */
	prvSetupTimerInterrupt();
	
	/* Start the first task. */
    asm volatile (  " movia r2, restore_sp_from_pxCurrentTCB        \n"
                    " jmp r2                                          " );

	/* Should not get here! */
	return 0;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
	/* It is unlikely that the NIOS2 port will require this function as there
	is nothing to return to.  */
}
/*-----------------------------------------------------------*/

/*
 * Setup the systick timer to generate the tick interrupts at the required
 * frequency.
 */
void prvSetupTimerInterrupt( void )
{
	/* Try to register the interrupt handler. */
	if ( -EINVAL == alt_irq_register( SYS_CLK_IRQ, 0x0, vPortSysTickHandler ) )
	{ 
		/* Failed to install the Interrupt Handler. */
		asm( "break" );
	}
	else
	{
		/* Configure SysTick to interrupt at the requested rate. */
		IOWR_ALTERA_AVALON_TIMER_CONTROL( SYS_CLK_BASE, ALTERA_AVALON_TIMER_CONTROL_STOP_MSK );
		IOWR_ALTERA_AVALON_TIMER_PERIODL( SYS_CLK_BASE, ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) & 0xFFFF );
		IOWR_ALTERA_AVALON_TIMER_PERIODH( SYS_CLK_BASE, ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) >> 16 );
		IOWR_ALTERA_AVALON_TIMER_CONTROL( SYS_CLK_BASE, ALTERA_AVALON_TIMER_CONTROL_CONT_MSK | ALTERA_AVALON_TIMER_CONTROL_START_MSK | ALTERA_AVALON_TIMER_CONTROL_ITO_MSK );	
	} 

	/* Clear any already pending interrupts generated by the Timer. */
	IOWR_ALTERA_AVALON_TIMER_STATUS( SYS_CLK_BASE, ~ALTERA_AVALON_TIMER_STATUS_TO_MSK );
}
/*-----------------------------------------------------------*/

void vPortSysTickHandler( void * context, alt_u32 id )
{
	/* Increment the kernel tick. */
	if( xTaskIncrementTick() != pdFALSE )
	{
        vTaskSwitchContext();
	}
		
	/* Clear the interrupt. */
	IOWR_ALTERA_AVALON_TIMER_STATUS( SYS_CLK_BASE, ~ALTERA_AVALON_TIMER_STATUS_TO_MSK );
}
/*-----------------------------------------------------------*/

/** This function is a re-implementation of the Altera provided function.
 * The function is re-implemented to prevent it from enabling an interrupt
 * when it is registered. Interrupts should only be enabled after the FreeRTOS.org
 * kernel has its scheduler started so that contexts are saved and switched 
 * correctly.
 */
int alt_irq_register( alt_u32 id, void* context, void (*handler)(void*, alt_u32) )
{
	int rc = -EINVAL;  
	alt_irq_context status;

	if (id < ALT_NIRQ)
	{
		/* 
		 * interrupts are disabled while the handler tables are updated to ensure
		 * that an interrupt doesn't occur while the tables are in an inconsistent
		 * state.
		 */
	
		status = alt_irq_disable_all ();
	
		alt_irq[id].handler = handler;
		alt_irq[id].context = context;
	
		rc = (handler) ? alt_irq_enable (id): alt_irq_disable (id);
	
		/* alt_irq_enable_all(status); This line is removed to prevent the interrupt from being immediately enabled. */
	}
    
	return rc; 
}
/*-----------------------------------------------------------*/