FreeRTOS-Kernel/Source/portable/MPLAB/PIC32MX/port.c

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*/

/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the PIC32MX port.
  *----------------------------------------------------------*/

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

/* Hardware specifics. */
#define portTIMER_PRESCALE 8

/* Bits within various registers. */
#define portIE_BIT					( 0x00000001 )
#define portEXL_BIT					( 0x00000002 )
#define portSW0_ENABLE				( 0x00000100 )

/* The EXL bit is set to ensure interrupts do not occur while the context of
the first task is being restored. */
#define portINITIAL_SR				( portIE_BIT | portEXL_BIT | portSW0_ENABLE )

/* Records the interrupt nesting depth.  This starts at one as it will be
decremented to 0 when the first task starts. */
volatile unsigned portBASE_TYPE uxInterruptNesting = 0x01;

/* Stores the task stack pointer when a switch is made to use the system stack. */
unsigned portBASE_TYPE uxSavedTaskStackPointer = 0;

/* The stack used by interrupt service routines that cause a context switch. */
portSTACK_TYPE xISRStack[ configISR_STACK_SIZE ] = { 0 };

/* The top of stack value ensures there is enough space to store 6 registers on 
the callers stack, as some functions seem to want to do this. */
const portBASE_TYPE * const xISRStackTop = &( xISRStack[ configISR_STACK_SIZE - 7 ] );

/* 
 * Place the prototype here to ensure the interrupt vector is correctly installed. 
 * Note that because the interrupt is written in assembly, the IPL setting in the
 * following line of code has no effect.  The interrupt priority is set by the
 * call to ConfigIntTimer1() in prvSetupTimerInterrupt(). 
 */
extern void __attribute__( (interrupt(ipl1), vector(_TIMER_1_VECTOR))) vT1InterruptHandler( void );

/*
 * The software interrupt handler that performs the yield.  Note that, because
 * the interrupt is written in assembly, the IPL setting in the following line of
 * code has no effect.  The interrupt priority is set by the call to 
 * mConfigIntCoreSW0() in xPortStartScheduler(). 
 */
void __attribute__( (interrupt(ipl1), vector(_CORE_SOFTWARE_0_VECTOR))) vPortYieldISR( void );

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

/* 
 * See header file for description. 
 */
portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
{
	*pxTopOfStack = (portSTACK_TYPE) 0xDEADBEEF;
	pxTopOfStack--;

	*pxTopOfStack = (portSTACK_TYPE) 0x12345678;	/* Word to which the stack pointer will be left pointing after context restore. */
	pxTopOfStack--;

	*pxTopOfStack = (portSTACK_TYPE) _CP0_GET_CAUSE();
	pxTopOfStack--;

	*pxTopOfStack = (portSTACK_TYPE) portINITIAL_SR; /* CP0_STATUS */
	pxTopOfStack--;

	*pxTopOfStack = (portSTACK_TYPE) pxCode; 		/* CP0_EPC */
	pxTopOfStack--;

	*pxTopOfStack = (portSTACK_TYPE) NULL;  		/* ra */
	pxTopOfStack -= 15;

	*pxTopOfStack = (portSTACK_TYPE) pvParameters; /* Parameters to pass in */
	pxTopOfStack -= 14;

	*pxTopOfStack = (portSTACK_TYPE) 0x00000000; 	/* critical nesting level - no longer used. */
	pxTopOfStack--;
	
	return pxTopOfStack;
}
/*-----------------------------------------------------------*/

/*
 * Setup a timer for a regular tick.
 */
void prvSetupTimerInterrupt( void )
{
const unsigned long ulCompareMatch = ( (configPERIPHERAL_CLOCK_HZ / portTIMER_PRESCALE) / configTICK_RATE_HZ ) - 1;

	OpenTimer1( ( T1_ON | T1_PS_1_8 | T1_SOURCE_INT ), ulCompareMatch );
	ConfigIntTimer1( T1_INT_ON | configKERNEL_INTERRUPT_PRIORITY );
}
/*-----------------------------------------------------------*/

void vPortEndScheduler(void)
{
	/* It is unlikely that the scheduler for the PIC port will get stopped
	once running.  If required disable the tick interrupt here, then return 
	to xPortStartScheduler(). */
	for( ;; );
}
/*-----------------------------------------------------------*/

portBASE_TYPE xPortStartScheduler( void )
{
extern void vPortStartFirstTask( void );
extern void *pxCurrentTCB;

	/* Setup the software interrupt. */
	mConfigIntCoreSW0( CSW_INT_ON | configKERNEL_INTERRUPT_PRIORITY | CSW_INT_SUB_PRIOR_0 );

	/* Setup the timer to generate the tick.  Interrupts will have been 
	disabled by the time we get here. */
	prvSetupTimerInterrupt();

	/* Kick off the highest priority task that has been created so far. 
	Its stack location is loaded into uxSavedTaskStackPointer. */
	uxSavedTaskStackPointer = *( unsigned portBASE_TYPE * ) pxCurrentTCB;
	vPortStartFirstTask();

	/* Should never get here as the tasks will now be executing. */
	return pdFALSE;
}
/*-----------------------------------------------------------*/

void vPortIncrementTick( void )
{
unsigned portBASE_TYPE uxSavedStatus;

	uxSavedStatus = uxPortSetInterruptMaskFromISR();
		vTaskIncrementTick();
	vPortClearInterruptMaskFromISR( uxSavedStatus );
	
	/* If we are using the preemptive scheduler then we might want to select
	a different task to execute. */
	#if configUSE_PREEMPTION == 1
		SetCoreSW0();
	#endif /* configUSE_PREEMPTION */

	/* Clear timer 0 interrupt. */
	mT1ClearIntFlag();
}
/*-----------------------------------------------------------*/

unsigned portBASE_TYPE uxPortSetInterruptMaskFromISR( void )
{
unsigned portBASE_TYPE uxSavedStatusRegister;

	asm volatile ( "di" );
	uxSavedStatusRegister = _CP0_GET_STATUS() | 0x01;
	/* This clears the IPL bits, then sets them to 
	configMAX_SYSCALL_INTERRUPT_PRIORITY.  This function should not be called
	from an interrupt that has a priority above 
	configMAX_SYSCALL_INTERRUPT_PRIORITY so, when used correctly, the action
	can only result in the IPL being unchanged or raised, and therefore never
	lowered. */
	_CP0_SET_STATUS( ( ( uxSavedStatusRegister & ( ~portALL_IPL_BITS ) ) ) | ( configMAX_SYSCALL_INTERRUPT_PRIORITY << portIPL_SHIFT ) );

	return uxSavedStatusRegister;
}
/*-----------------------------------------------------------*/

void vPortClearInterruptMaskFromISR( unsigned portBASE_TYPE uxSavedStatusRegister )
{
	_CP0_SET_STATUS( uxSavedStatusRegister );
}
/*-----------------------------------------------------------*/