FreeRTOS/Source/portable/GCC/HCS12/port.c

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*/

/* GCC/HCS12 port by Jefferson L Smith, 2005 */

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

/* Port includes */
#include <sys/ports_def.h>

/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the HCS12 port.
 *----------------------------------------------------------*/


/*
 * Configure a timer to generate the RTOS tick at the frequency specified 
 * within FreeRTOSConfig.h.
 */
static void prvSetupTimerInterrupt( void );

/* NOTE: Interrupt service routines must be in non-banked memory - as does the
scheduler startup function. */
#define ATTR_NEAR	__attribute__((near))

/* Manual context switch function.  This is the SWI ISR. */
// __attribute__((interrupt))
void ATTR_NEAR vPortYield( void );

/* Tick context switch function.  This is the timer ISR. */
// __attribute__((interrupt))
void ATTR_NEAR vPortTickInterrupt( void );

/* Function in non-banked memory which actually switches to first task. */
portBASE_TYPE ATTR_NEAR xStartSchedulerNear( void );

/* Calls to portENTER_CRITICAL() can be nested.  When they are nested the 
critical section should not be left (i.e. interrupts should not be re-enabled)
until the nesting depth reaches 0.  This variable simply tracks the nesting 
depth.  Each task maintains it's own critical nesting depth variable so 
uxCriticalNesting is saved and restored from the task stack during a context
switch. */
volatile unsigned portBASE_TYPE uxCriticalNesting = 0x80;  // un-initialized

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

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


	/* Setup the initial stack of the task.  The stack is set exactly as 
	expected by the portRESTORE_CONTEXT() macro.  In this case the stack as
	expected by the HCS12 RTI instruction. */


	/* The address of the task function is placed in the stack byte at a time. */
	*pxTopOfStack   = ( portSTACK_TYPE ) *( ((portSTACK_TYPE *) (&pxCode) ) + 1 );
	*--pxTopOfStack = ( portSTACK_TYPE ) *( ((portSTACK_TYPE *) (&pxCode) ) + 0 );

	/* Next are all the registers that form part of the task context. */

	/* Y register */
	*--pxTopOfStack = ( portSTACK_TYPE ) 0xff;
	*--pxTopOfStack = ( portSTACK_TYPE ) 0xee;

	/* X register */
	*--pxTopOfStack = ( portSTACK_TYPE ) 0xdd;
	*--pxTopOfStack = ( portSTACK_TYPE ) 0xcc;
 
	/* A register contains parameter high byte. */
	*--pxTopOfStack = ( portSTACK_TYPE ) *( ((portSTACK_TYPE *) (&pvParameters) ) + 0 );

	/* B register contains parameter low byte. */
	*--pxTopOfStack = ( portSTACK_TYPE ) *( ((portSTACK_TYPE *) (&pvParameters) ) + 1 );

	/* CCR: Note that when the task starts interrupts will be enabled since
	"I" bit of CCR is cleared */
	*--pxTopOfStack = ( portSTACK_TYPE ) 0x80;		// keeps Stop disabled (MCU default)
	
	/* tmp softregs used by GCC. Values right now don't	matter. */
	__asm("\n\
		movw _.frame, 2,-%0							\n\
		movw _.tmp, 2,-%0							\n\
		movw _.z, 2,-%0								\n\
		movw _.xy, 2,-%0							\n\
		;movw _.d2, 2,-%0							\n\
		;movw _.d1, 2,-%0							\n\
	": "=A"(pxTopOfStack) : "0"(pxTopOfStack) );

	#ifdef BANKED_MODEL
		/* The page of the task. */
		*--pxTopOfStack = 0x30;      // can only directly start in PPAGE 0x30
	#endif
	
	/* The critical nesting depth is initialised with 0 (meaning not in
	a critical section). */
	*--pxTopOfStack = ( portSTACK_TYPE ) 0x00;


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

void vPortEndScheduler( void )
{
	/* It is unlikely that the HCS12 port will get stopped. */
}
/*-----------------------------------------------------------*/

static void prvSetupTimerInterrupt( void )
{
	/* Enable hardware RTI timer */
	/* Ignores configTICK_RATE_HZ */
	RTICTL = 0x50;			// 16 MHz xtal: 976.56 Hz, 1024mS 
	CRGINT |= 0x80;			// RTIE
}
/*-----------------------------------------------------------*/

portBASE_TYPE xPortStartScheduler( void )
{
	/* xPortStartScheduler() does not start the scheduler directly because 
	the header file containing the xPortStartScheduler() prototype is part 
	of the common kernel code, and therefore cannot use the CODE_SEG pragma. 
	Instead it simply calls the locally defined xNearStartScheduler() - 
	which does use the CODE_SEG pragma. */

	short register d;
	__asm ("jmp  xStartSchedulerNear		; will never return": "=d"(d));
	return d;
}
/*-----------------------------------------------------------*/

portBASE_TYPE xStartSchedulerNear( void )
{
	/* Configure the timer that will generate the RTOS tick.  Interrupts are
	disabled when this function is called. */
	prvSetupTimerInterrupt();

	/* Restore the context of the first task. */
	portRESTORE_CONTEXT();

	portISR_TAIL();

	/* Should not get here! */
	return pdFALSE;
}
/*-----------------------------------------------------------*/

/*
 * Context switch functions.  These are interrupt service routines.
 */

/*
 * Manual context switch forced by calling portYIELD().  This is the SWI
 * handler.
 */
void vPortYield( void )
{
	portISR_HEAD();
	/* NOTE: This is the trap routine (swi) although not defined as a trap.
	   It will fill the stack the same way as an ISR in order to mix preemtion
	   and cooperative yield. */

	portSAVE_CONTEXT();
	vTaskSwitchContext();
	portRESTORE_CONTEXT();

	portISR_TAIL();
}
/*-----------------------------------------------------------*/

/*
 * RTOS tick interrupt service routine.  If the cooperative scheduler is 
 * being used then this simply increments the tick count.  If the 
 * preemptive scheduler is being used a context switch can occur.
 */
void vPortTickInterrupt( void )
{
	portISR_HEAD();

	/* Clear tick timer flag */
	CRGFLG = 0x80;

	#if configUSE_PREEMPTION == 1
	{
		/* A context switch might happen so save the context. */
		portSAVE_CONTEXT();

		/* Increment the tick ... */
		vTaskIncrementTick();

		/* ... then see if the new tick value has necessitated a
		context switch. */
		vTaskSwitchContext();

		/* Restore the context of a task - which may be a different task
		to that interrupted. */
		portRESTORE_CONTEXT();
	}
	#else
	{
		vTaskIncrementTick();
	}
	#endif

	portISR_TAIL();
}