/*
    FreeRTOS V6.0.0 - Copyright (C) 2009 Real Time Engineers Ltd.

    This file is part of the FreeRTOS distribution.

    FreeRTOS is free software; you can redistribute it and/or modify it    under
    the terms of the GNU General Public License (version 2) as published by the
    Free Software Foundation and modified by the FreeRTOS exception.
    **NOTE** The exception to the GPL is included to allow you to distribute a
    combined work that includes FreeRTOS without being obliged to provide the
    source code for proprietary components outside of the FreeRTOS kernel.
    Alternative commercial license and support terms are also available upon
    request.  See the licensing section of http://www.FreeRTOS.org for full
    license details.

    FreeRTOS is distributed in the hope that it will be useful,    but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
    more details.

    You should have received a copy of the GNU General Public License along
    with FreeRTOS; if not, write to the Free Software Foundation, Inc., 59
    Temple Place, Suite 330, Boston, MA  02111-1307  USA.


    ***************************************************************************
    *                                                                         *
    * The FreeRTOS eBook and reference manual are available to purchase for a *
    * small fee. Help yourself get started quickly while also helping the     *
    * FreeRTOS project! See http://www.FreeRTOS.org/Documentation for details *
    *                                                                         *
    ***************************************************************************

    1 tab == 4 spaces!

    Please ensure to read the configuration and relevant port sections of the
    online documentation.

    http://www.FreeRTOS.org - Documentation, latest information, license and
    contact details.

    http://www.SafeRTOS.com - A version that is certified for use in safety
    critical systems.

    http://www.OpenRTOS.com - Commercial support, development, porting,
    licensing and training services.
*/

/*
Changes from V1.00:
	
	+ pxPortInitialiseStack() now initialises the stack of new tasks to the 
	  same format used by the compiler.  This allows the compiler generated
	  interrupt mechanism to be used for context switches.

Changes from V2.4.2:

	+ pvPortMalloc and vPortFree have been removed.  The projects now use
	  the definitions from the source/portable/MemMang directory.

Changes from V2.6.1:

	+ usPortCheckFreeStackSpace() has been moved to tasks.c.
*/

	

#include <stdlib.h>
#include "FreeRTOS.h"

/*-----------------------------------------------------------*/

/* See header file for description. */
portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
{
portSTACK_TYPE DS_Reg = 0, *pxOriginalSP;

	/* Place a few bytes of known values on the bottom of the stack. 
	This is just useful for debugging. */

	*pxTopOfStack = 0x1111;
	pxTopOfStack--;
	*pxTopOfStack = 0x2222;
	pxTopOfStack--;
	*pxTopOfStack = 0x3333;
	pxTopOfStack--;
	*pxTopOfStack = 0x4444;
	pxTopOfStack--;
	*pxTopOfStack = 0x5555;
	pxTopOfStack--;


	/*lint -e950 -e611 -e923 Lint doesn't like this much - but nothing I can do about it. */

	/* We are going to start the scheduler using a return from interrupt
	instruction to load the program counter, so first there would be the
	status register and interrupt return address.  We make this the start 
	of the task. */
	*pxTopOfStack = portINITIAL_SW; 
	pxTopOfStack--;
	*pxTopOfStack = FP_SEG( pxCode );
	pxTopOfStack--;
	*pxTopOfStack = FP_OFF( pxCode );
	pxTopOfStack--;

	/* We are going to setup the stack for the new task to look like
	the stack frame was setup by a compiler generated ISR.  We need to know
	the address of the existing stack top to place in the SP register within
	the stack frame.  pxOriginalSP holds SP before (simulated) pusha was 
	called. */
	pxOriginalSP = pxTopOfStack;

	/* The remaining registers would be pushed on the stack by our context 
	switch function.  These are loaded with values simply to make debugging
	easier. */
	*pxTopOfStack = FP_OFF( pvParameters );		/* AX */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xCCCC;	/* CX */
	pxTopOfStack--;
	*pxTopOfStack = FP_SEG( pvParameters );		/* DX */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xBBBB;	/* BX */
	pxTopOfStack--;
	*pxTopOfStack = FP_OFF( pxOriginalSP );		/* SP */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xBBBB;	/* BP */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0x0123;	/* SI */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xDDDD;	/* DI */

	/* We need the true data segment. */
	__asm{	MOV DS_Reg, DS };

	pxTopOfStack--;
	*pxTopOfStack = DS_Reg;	/* DS */

	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xEEEE;	/* ES */

	/* The AX register is pushed again twice - don't know why. */
	pxTopOfStack--;
	*pxTopOfStack = FP_OFF( pvParameters );		/* AX */
	pxTopOfStack--;
	*pxTopOfStack = FP_OFF( pvParameters );		/* AX */


	#ifdef DEBUG_BUILD
		/* The compiler adds space to each ISR stack if building to
		include debug information.  Presumably this is used by the
		debugger - we don't need to initialise it to anything just
		make sure it is there. */
		pxTopOfStack--;
	#endif

	/*lint +e950 +e611 +e923 */

	return pxTopOfStack;
}
/*-----------------------------------------------------------*/