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FreeRTOS V7.2.0 - Copyright (C) 2012 Real Time Engineers Ltd.
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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 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: and also obtained
by writing to Richard Barry, contact details for whom are available on the
FreeRTOS WEB site.
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*************************************************************************** - Documentation, training, latest information,
license and contact details. - A selection of FreeRTOS ecosystem products,
including FreeRTOS+Trace - an indispensable productivity tool.
Real Time Engineers ltd license FreeRTOS to High Integrity Systems, who sell
the code with commercial support, indemnification, and middleware, under
the OpenRTOS brand: High Integrity Systems also
provide a safety engineered and independently SIL3 certified version under
the SafeRTOS brand:
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 = 0x2222;
*pxTopOfStack = 0x3333;
*pxTopOfStack = 0x4444;
*pxTopOfStack = 0x5555;
/*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 = FP_SEG( pxCode );
*pxTopOfStack = FP_OFF( pxCode );
/* 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 = ( portSTACK_TYPE ) 0xCCCC; /* CX */
*pxTopOfStack = FP_SEG( pvParameters ); /* DX */
*pxTopOfStack = ( portSTACK_TYPE ) 0xBBBB; /* BX */
*pxTopOfStack = FP_OFF( pxOriginalSP ); /* SP */
*pxTopOfStack = ( portSTACK_TYPE ) 0xBBBB; /* BP */
*pxTopOfStack = ( portSTACK_TYPE ) 0x0123; /* SI */
*pxTopOfStack = ( portSTACK_TYPE ) 0xDDDD; /* DI */
/* We need the true data segment. */
__asm{ MOV DS_Reg, DS };
*pxTopOfStack = DS_Reg; /* DS */
*pxTopOfStack = ( portSTACK_TYPE ) 0xEEEE; /* ES */
/* The AX register is pushed again twice - don't know why. */
*pxTopOfStack = FP_OFF( pvParameters ); /* AX */
*pxTopOfStack = FP_OFF( pvParameters ); /* AX */
/* 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. */
/*lint +e950 +e611 +e923 */
return pxTopOfStack;