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

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

	/* Leave space to write the size of the stack as the first byte. */
	pxStartOfStack = pxTopOfStack;
	pxTopOfStack++;

	/* Place a few bytes of known values on the bottom of the stack. 
	This is just useful for debugging and can be uncommented if required.
	*pxTopOfStack = 0x11;
	pxTopOfStack++;
	*pxTopOfStack = 0x22;
	pxTopOfStack++;
	*pxTopOfStack = 0x33;
	pxTopOfStack++;
	*/

	/* Simulate how the stack would look after a call to the scheduler tick 
	ISR. 

	The return address that would have been pushed by the MCU. */
	ulAddress = ( unsigned portLONG ) pxCode;
	*pxTopOfStack = ( portSTACK_TYPE ) ulAddress;
	ulAddress >>= 8;
	pxTopOfStack++;
	*pxTopOfStack = ( portSTACK_TYPE ) ( ulAddress );
	pxTopOfStack++;

	/* Next all the registers will have been pushed by portSAVE_CONTEXT(). */
	*pxTopOfStack = 0xaa;	/* acc */
	pxTopOfStack++;	

	/* We want tasks to start with interrupts enabled. */
	*pxTopOfStack = portGLOBAL_INTERRUPT_BIT;
	pxTopOfStack++;

	/* The function parameters will be passed in the DPTR and B register as
	a three byte generic pointer is used. */
	ulAddress = ( unsigned portLONG ) pvParameters;
	*pxTopOfStack = ( portSTACK_TYPE ) ulAddress;	/* DPL */
	ulAddress >>= 8;
	*pxTopOfStack++;
	*pxTopOfStack = ( portSTACK_TYPE ) ulAddress;	/* DPH */
	ulAddress >>= 8;
	pxTopOfStack++;
	*pxTopOfStack = ( portSTACK_TYPE ) ulAddress;	/* b */
	pxTopOfStack++;

	/* The remaining registers are straight forward. */
	*pxTopOfStack = 0x02;	/* R2 */
	pxTopOfStack++;
	*pxTopOfStack = 0x03;	/* R3 */
	pxTopOfStack++;
	*pxTopOfStack = 0x04;	/* R4 */
	pxTopOfStack++;
	*pxTopOfStack = 0x05;	/* R5 */
	pxTopOfStack++;
	*pxTopOfStack = 0x06;	/* R6 */
	pxTopOfStack++;
	*pxTopOfStack = 0x07;	/* R7 */
	pxTopOfStack++;
	*pxTopOfStack = 0x00;	/* R0 */
	pxTopOfStack++;
	*pxTopOfStack = 0x01;	/* R1 */
	pxTopOfStack++;
	*pxTopOfStack = 0x00;	/* PSW */
	pxTopOfStack++;
	*pxTopOfStack = 0xbb;	/* BP */

	/* Dont increment the stack size here as we don't want to include
	the stack size byte as part of the stack size count.

	Finally we place the stack size at the beginning. */
	*pxStartOfStack = ( portSTACK_TYPE ) ( pxTopOfStack - pxStartOfStack );

	/* Unlike most ports, we return the start of the stack as this is where the
	size of the stack is stored. */
	return pxStartOfStack;
}
/*-----------------------------------------------------------*/

/* 
 * See header file for description. 
 */
portBASE_TYPE xPortStartScheduler( void )
{
	/* Setup timer 2 to generate the RTOS tick. */
	prvSetupTimerInterrupt();	

	/* Make sure we start with the expected SFR page.  This line should not
	really be required. */
	SFRPAGE = 0;

	/* Copy the stack for the first task to execute from XRAM into the stack,
	restore the task context from the new stack, then start running the task. */
	portCOPY_XRAM_TO_STACK();
	portRESTORE_CONTEXT();

	/* Should never get here! */
	return pdTRUE;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
	/* Not implemented for this port. */
}
/*-----------------------------------------------------------*/

/*
 * Manual context switch.  The first thing we do is save the registers so we
 * can use a naked attribute.
 */
void vPortYield( void ) _naked
{
	/* Save the execution context onto the stack, then copy the entire stack
	to XRAM.  This is necessary as the internal RAM is only large enough to
	hold one stack, and we want one per task. 
	
	PERFORMANCE COULD BE IMPROVED BY ONLY COPYING TO XRAM IF A TASK SWITCH
	IS REQUIRED. */
	portSAVE_CONTEXT();
	portCOPY_STACK_TO_XRAM();

	/* Call the standard scheduler context switch function. */
	vTaskSwitchContext();

	/* Copy the stack of the task about to execute from XRAM into RAM and
	restore it's context ready to run on exiting. */
	portCOPY_XRAM_TO_STACK();
	portRESTORE_CONTEXT();
}
/*-----------------------------------------------------------*/

#if configUSE_PREEMPTION == 1
	void vTimer2ISR( void ) interrupt 5 _naked
	{
		/* Preemptive context switch function triggered by the timer 2 ISR.
		This does the same as vPortYield() (see above) with the addition
		of incrementing the RTOS tick count. */

		portSAVE_CONTEXT();
		portCOPY_STACK_TO_XRAM();

		vTaskIncrementTick();
		vTaskSwitchContext();
		
		portCLEAR_INTERRUPT_FLAG();
		portCOPY_XRAM_TO_STACK();
		portRESTORE_CONTEXT();
	}
#else
	void vTimer2ISR( void ) interrupt 5
	{
		/* When using the cooperative scheduler the timer 2 ISR is only 
		required to increment the RTOS tick count. */

		vTaskIncrementTick();
		portCLEAR_INTERRUPT_FLAG();
	}
#endif
/*-----------------------------------------------------------*/

static void prvSetupTimerInterrupt( void )
{
unsigned portCHAR ucOriginalSFRPage;

/* Constants calculated to give the required timer capture values. */
const unsigned portLONG ulTicksPerSecond = configCPU_CLOCK_HZ / portCLOCK_DIVISOR;
const unsigned portLONG ulCaptureTime = ulTicksPerSecond / configTICK_RATE_HZ;
const unsigned portLONG ulCaptureValue = portMAX_TIMER_VALUE - ulCaptureTime;
const unsigned portCHAR ucLowCaptureByte = ( unsigned portCHAR ) ( ulCaptureValue & ( unsigned portLONG ) 0xff );
const unsigned portCHAR ucHighCaptureByte = ( unsigned portCHAR ) ( ulCaptureValue >> ( unsigned portLONG ) 8 );

	/* NOTE:  This uses a timer only present on 8052 architecture. */

	/* Remember the current SFR page so we can restore it at the end of the
	function. */
	ucOriginalSFRPage = SFRPAGE;
	SFRPAGE = 0;

	/* TMR2CF can be left in its default state. */	
	TMR2CF = ( unsigned portCHAR ) 0;

	/* Setup the overflow reload value. */
	RCAP2L = ucLowCaptureByte;
	RCAP2H = ucHighCaptureByte;

	/* The initial load is performed manually. */
	TMR2L = ucLowCaptureByte;
	TMR2H = ucHighCaptureByte;

	/* Enable the timer 2 interrupts. */
	IE |= portTIMER_2_INTERRUPT_ENABLE;

	/* Interrupts are disabled when this is called so the timer can be started
	here. */
	TMR2CN = portENABLE_TIMER;

	/* Restore the original SFR page. */
	SFRPAGE = ucOriginalSFRPage;
}