FreeRTOS/Source/portable/RVDS/ARM7_LPC21xx/port.c

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    This file is part of the FreeRTOS distribution.

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*/


/* Standard includes. */
#include <stdlib.h>

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

/* Constants required to setup the initial task context. */
#define portINITIAL_SPSR				( ( portSTACK_TYPE ) 0x1f ) /* System mode, ARM mode, interrupts enabled. */
#define portTHUMB_MODE_BIT				( ( portSTACK_TYPE ) 0x20 )
#define portINSTRUCTION_SIZE			( ( portSTACK_TYPE ) 4 )
#define portNO_CRITICAL_SECTION_NESTING	( ( portSTACK_TYPE ) 0 )

/* Constants required to setup the tick ISR. */
#define portENABLE_TIMER			( ( unsigned portCHAR ) 0x01 )
#define portPRESCALE_VALUE			0x00
#define portINTERRUPT_ON_MATCH		( ( unsigned portLONG ) 0x01 )
#define portRESET_COUNT_ON_MATCH	( ( unsigned portLONG ) 0x02 )

/* Constants required to setup the VIC for the tick ISR. */
#define portTIMER_VIC_CHANNEL		( ( unsigned portLONG ) 0x0004 )
#define portTIMER_VIC_CHANNEL_BIT	( ( unsigned portLONG ) 0x0010 )
#define portTIMER_VIC_ENABLE		( ( unsigned portLONG ) 0x0020 )

/* Constants required to handle interrupts. */
#define portTIMER_MATCH_ISR_BIT		( ( unsigned portCHAR ) 0x01 )
#define portCLEAR_VIC_INTERRUPT		( ( unsigned portLONG ) 0 )

/*-----------------------------------------------------------*/

/* The code generated by the Keil compiler does not maintain separate
stack and frame pointers. The portENTER_CRITICAL macro cannot therefore
use the stack as per other ports.  Instead a variable is used to keep
track of the critical section nesting.  This variable has to be stored
as part of the task context and must be initialised to a non zero value. */

#define portNO_CRITICAL_NESTING		( ( unsigned portLONG ) 0 )
volatile unsigned portLONG ulCriticalNesting = 9999UL;

/*-----------------------------------------------------------*/

/* Setup the timer to generate the tick interrupts. */
static void prvSetupTimerInterrupt( void );

/* 
 * The scheduler can only be started from ARM mode, so 
 * vPortStartFirstSTask() is defined in portISR.c. 
 */
extern __asm void vPortStartFirstTask( void );

/*-----------------------------------------------------------*/

/* 
 * See header file for description. 
 */
portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
{
portSTACK_TYPE *pxOriginalTOS;

	/* Setup the initial stack of the task.  The stack is set exactly as 
	expected by the portRESTORE_CONTEXT() macro.

	Remember where the top of the (simulated) stack is before we place 
	anything on it. */
	pxOriginalTOS = pxTopOfStack;
	
	/* To ensure asserts in tasks.c don't fail, although in this case the assert
	is not really required. */
	pxTopOfStack--;

	/* 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 = ( portSTACK_TYPE ) pxCode + portINSTRUCTION_SIZE;		
	pxTopOfStack--;

	*pxTopOfStack = ( portSTACK_TYPE ) 0xaaaaaaaa;	/* R14 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) pxOriginalTOS; /* Stack used when task starts goes in R13. */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0x12121212;	/* R12 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x11111111;	/* R11 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x10101010;	/* R10 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x09090909;	/* R9 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x08080808;	/* R8 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x07070707;	/* R7 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x06060606;	/* R6 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x05050505;	/* R5 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x04040404;	/* R4 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x03030303;	/* R3 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x02020202;	/* R2 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) 0x01010101;	/* R1 */
	pxTopOfStack--;	
	*pxTopOfStack = ( portSTACK_TYPE ) pvParameters; /* R0 */
	pxTopOfStack--;

	/* The last thing onto the stack is the status register, which is set for
	system mode, with interrupts enabled. */
	*pxTopOfStack = ( portSTACK_TYPE ) portINITIAL_SPSR;

	if( ( ( unsigned long ) pxCode & 0x01UL ) != 0x00UL )
	{
		/* We want the task to start in thumb mode. */
		*pxTopOfStack |= portTHUMB_MODE_BIT;
	}

	pxTopOfStack--;

	/* The code generated by the Keil compiler does not maintain separate
	stack and frame pointers. The portENTER_CRITICAL macro cannot therefore
	use the stack as per other ports.  Instead a variable is used to keep
	track of the critical section nesting.  This variable has to be stored
	as part of the task context and is initially set to zero. */
	*pxTopOfStack = portNO_CRITICAL_SECTION_NESTING;

	return pxTopOfStack;
}
/*-----------------------------------------------------------*/

portBASE_TYPE xPortStartScheduler( void )
{
	/* Start the timer that generates the tick ISR. */
	prvSetupTimerInterrupt();

	/* Start the first task.  This is done from portISR.c as ARM mode must be
	used. */
	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 this is required - stop the tick ISR then
	return back to main. */
}
/*-----------------------------------------------------------*/

#if configUSE_PREEMPTION == 0

	/* 
	 * The cooperative scheduler requires a normal IRQ service routine to 
	 * simply increment the system tick. 
	 */
	void vNonPreemptiveTick( void ) __irq;
	void vNonPreemptiveTick( void ) __irq
	{
		/* Increment the tick count - this may make a delaying task ready
		to run - but a context switch is not performed. */		
		xTaskIncrementTick();

		T0IR = portTIMER_MATCH_ISR_BIT;				/* Clear the timer event */
		VICVectAddr = portCLEAR_VIC_INTERRUPT;		/* Acknowledge the Interrupt */
	}

 #else

	/*
	 **************************************************************************
	 * The preemptive scheduler ISR is written in assembler and can be found   
	 * in the portASM.s file. This will only get used if portUSE_PREEMPTION
	 * is set to 1 in portmacro.h
	 ************************************************************************** 
	 */

	  void vPreemptiveTick( void );

#endif
/*-----------------------------------------------------------*/

static void prvSetupTimerInterrupt( void )
{
unsigned portLONG ulCompareMatch;

	/* A 1ms tick does not require the use of the timer prescale.  This is
	defaulted to zero but can be used if necessary. */
	T0PR = portPRESCALE_VALUE;

	/* Calculate the match value required for our wanted tick rate. */
	ulCompareMatch = configCPU_CLOCK_HZ / configTICK_RATE_HZ;

	/* Protect against divide by zero.  Using an if() statement still results
	in a warning - hence the #if. */
	#if portPRESCALE_VALUE != 0
	{
		ulCompareMatch /= ( portPRESCALE_VALUE + 1 );
	}
	#endif

	T0MR0 = ulCompareMatch;

	/* Generate tick with timer 0 compare match. */
	T0MCR = portRESET_COUNT_ON_MATCH | portINTERRUPT_ON_MATCH;

	/* Setup the VIC for the timer. */
	VICIntSelect &= ~( portTIMER_VIC_CHANNEL_BIT );
	VICIntEnable |= portTIMER_VIC_CHANNEL_BIT;
	
	/* The ISR installed depends on whether the preemptive or cooperative
	scheduler is being used. */
	#if configUSE_PREEMPTION == 1
	{	
		VICVectAddr0 = ( unsigned portLONG ) vPreemptiveTick;
	}
	#else
	{
		VICVectAddr0 = ( unsigned portLONG ) vNonPreemptiveTick;
	}
	#endif

	VICVectCntl0 = portTIMER_VIC_CHANNEL | portTIMER_VIC_ENABLE;

	/* Start the timer - interrupts are disabled when this function is called
	so it is okay to do this here. */
	T0TCR = portENABLE_TIMER;
}
/*-----------------------------------------------------------*/

void vPortEnterCritical( void )
{
	/* Disable interrupts as per portDISABLE_INTERRUPTS(); 							*/
	__disable_irq();

	/* 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 interrupts as per portEXIT_CRITICAL(). */
			__enable_irq();
		}
	}
}
/*-----------------------------------------------------------*/