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/*

    FreeRTOS V6.1.1 - Copyright (C) 2011 Real Time Engineers Ltd.

    ***************************************************************************

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    * then take a look at the FreeRTOS books - available as PDF or paperback  *

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    *        "Using the FreeRTOS Real Time Kernel - a Practical Guide"        *

    *                  http://www.FreeRTOS.org/Documentation                  *

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    * A pdf reference manual is also available.  Both are usually delivered   *

    * to your inbox within 20 minutes to two hours when purchased between 8am *

    * and 8pm GMT (although please allow up to 24 hours in case of            *

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    ***************************************************************************

    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.

    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 and the FreeRTOS license exception along with FreeRTOS; if not it

    can be viewed here: http://www.freertos.org/a00114.html and also obtained

    by writing to Richard Barry, contact details for whom are available on the

    FreeRTOS WEB site.

    1 tab == 4 spaces!

    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.

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    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;

}

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