FreeRTOS/Source/portable/GCC/ARM7_LPC2000/port.c

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*/


/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the ARM7 port.
 *
 * Components that can be compiled to either ARM or THUMB mode are
 * contained in this file.  The ISR routines, which can only be compiled
 * to ARM mode are contained in portISR.c.
 *----------------------------------------------------------*/


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

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

/* Constants required to setup the task context. */
#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 )
#define portNO_CRITICAL_SECTION_NESTING	( ( StackType_t ) 0 )

/* Constants required to setup the tick ISR. */
#define portENABLE_TIMER			( ( uint8_t ) 0x01 )
#define portPRESCALE_VALUE			0x00
#define portINTERRUPT_ON_MATCH		( ( uint32_t ) 0x01 )
#define portRESET_COUNT_ON_MATCH	( ( uint32_t ) 0x02 )

/* Constants required to setup the VIC for the tick ISR. */
#define portTIMER_VIC_CHANNEL		( ( uint32_t ) 0x0004 )
#define portTIMER_VIC_CHANNEL_BIT	( ( uint32_t ) 0x0010 )
#define portTIMER_VIC_ENABLE		( ( uint32_t ) 0x0020 )

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

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

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

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

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

	if( ( ( uint32_t ) pxCode & 0x01UL ) != 0x00 )
	{
		/* We want the task to start in thumb mode. */
		*pxTopOfStack |= portTHUMB_MODE_BIT;
	}

	pxTopOfStack--;

	/* Some optimisation levels use the stack differently to others.  This 
	means the 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_SECTION_NESTING;

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

BaseType_t xPortStartScheduler( void )
{
	/* Start the timer that generates the tick ISR.  Interrupts are disabled
	here already. */
	prvSetupTimerInterrupt();

	/* Start the first task. */
	vPortISRStartFirstTask();	

	/* 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.  */
}
/*-----------------------------------------------------------*/

/*
 * Setup the timer 0 to generate the tick interrupts at the required frequency.
 */
static void prvSetupTimerInterrupt( void )
{
uint32_t ulCompareMatch;
extern void ( vTickISR )( void );

	/* A 1ms tick does not require the use of the timer prescale.  This is
	defaulted to zero but can be used if necessary. */
	T0_PR = 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
	T0_MR0 = ulCompareMatch;

	/* Generate tick with timer 0 compare match. */
	T0_MCR = 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. */

	VICVectAddr0 = ( int32_t ) vTickISR;
	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. */
	T0_TCR = portENABLE_TIMER;
}
/*-----------------------------------------------------------*/