FreeRTOS/Source/portable/BCC/16BitDOS/common/portcomn.c

/*
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    All rights reserved

    VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.

    ***************************************************************************
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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 modification to the GPL is included to allow you to distribute
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    1 tab == 4 spaces!

    ***************************************************************************
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*/

/*
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 V2.6.1

	+ Move usPortCheckFreeStackSpace() to tasks.c.
*/


#include <dos.h>
#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;

	/* 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
	function call with parameters preamble. */
	
	*pxTopOfStack = FP_SEG( pvParameters );
	pxTopOfStack--;
	*pxTopOfStack = FP_OFF( pvParameters );
	pxTopOfStack--;
	*pxTopOfStack = FP_SEG( pxCode );
	pxTopOfStack--;
	*pxTopOfStack = FP_OFF( pxCode );
	pxTopOfStack--;

	/* Next the status register and interrupt return address. */
	*pxTopOfStack = portINITIAL_SW; 
	pxTopOfStack--;
	*pxTopOfStack = FP_SEG( pxCode );
	pxTopOfStack--;
	*pxTopOfStack = FP_OFF( pxCode );
	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 = ( portSTACK_TYPE ) 0xAAAA;	/* AX */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xBBBB;	/* BX */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xCCCC;	/* CX */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xDDDD;	/* DX */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xEEEE;	/* ES */
	pxTopOfStack--;

	/* We need the true data segment. */
	__asm{	MOV DS_Reg, DS };

	*pxTopOfStack = DS_Reg;						/* DS */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0x0123;	/* SI */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xDDDD;	/* DI */
	pxTopOfStack--;
	*pxTopOfStack = ( portSTACK_TYPE ) 0xBBBB;	/* BP */

	/*lint +e950 +e611 +e923 */

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