port.c

FreeRTOS is a portable, open source, mini Real Time Kernel - a free to download and royalty free RTO

/*
	FreeRTOS.org V5.2.0 - Copyright (C) 2003-2009 Richard Barry.

	This file is part of the FreeRTOS.org distribution.

	FreeRTOS.org 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.

	FreeRTOS.org 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.org; if not, write to the Free Software Foundation, Inc., 59 
	Temple Place, Suite 330, Boston, MA  02111-1307  USA.

	A special exception to the GPL is included to allow you to distribute a 
	combined work that includes FreeRTOS.org without being obliged to provide
	the source code for any proprietary components.  See the licensing section
	of http://www.FreeRTOS.org for full details.


	***************************************************************************
	*                                                                         *
	* Get the FreeRTOS eBook!  See http://www.FreeRTOS.org/Documentation      *
	*                                                                         *
	* This is a concise, step by step, 'hands on' guide that describes both   *
	* general multitasking concepts and FreeRTOS specifics. It presents and   *
	* explains numerous examples that are written using the FreeRTOS API.     *
	* Full source code for all the examples is provided in an accompanying    *
	* .zip file.                                                              *
	*                                                                         *
	***************************************************************************

	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.
*/

/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the Cygnal port.
 *----------------------------------------------------------*/

/* Standard includes. */
#include <string.h>

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

/* Constants required to setup timer 2 to produce the RTOS tick. */
#define portCLOCK_DIVISOR				( ( unsigned portLONG ) 12 )
#define portMAX_TIMER_VALUE				( ( unsigned portLONG ) 0xffff )
#define portENABLE_TIMER				( ( unsigned portCHAR ) 0x04 )
#define portTIMER_2_INTERRUPT_ENABLE	( ( unsigned portCHAR ) 0x20 )

/* The value used in the IE register when a task first starts. */
#define portGLOBAL_INTERRUPT_BIT	( ( portSTACK_TYPE ) 0x80 )

/* The value used in the PSW register when a task first starts. */
#define portINITIAL_PSW				( ( portSTACK_TYPE ) 0x00 )

/* Macro to clear the timer 2 interrupt flag. */
#define portCLEAR_INTERRUPT_FLAG()	TMR2CN &= ~0x80;

/* Used during a context switch to store the size of the stack being copied
to or from XRAM. */
data static unsigned portCHAR ucStackBytes;

/* Used during a context switch to point to the next byte in XRAM from/to which
a RAM byte is to be copied. */
xdata static portSTACK_TYPE * data pxXRAMStack;

/* Used during a context switch to point to the next byte in RAM from/to which
an XRAM byte is to be copied. */
data static portSTACK_TYPE * data pxRAMStack;

/* We require the address of the pxCurrentTCB variable, but don't want to know
any details of its type. */
typedef void tskTCB;
extern volatile tskTCB * volatile pxCurrentTCB;

/*
 * Setup the hardware to generate an interrupt off timer 2 at the required 
 * frequency.
 */
static void prvSetupTimerInterrupt( void );

/*-----------------------------------------------------------*/
/*
 * Macro that copies the current stack from internal RAM to XRAM.  This is 
 * required as the 8051 only contains enough internal RAM for a single stack, 
 * but we have a stack for every task.
 */
#define portCOPY_STACK_TO_XRAM()																\
{																								\
	/* pxCurrentTCB points to a TCB which itself points to the location into					\
	which the first	stack byte should be copied.  Set pxXRAMStack to point						\
	to the location into which the first stack byte is to be copied. */							\
	pxXRAMStack = ( xdata portSTACK_TYPE * ) *( ( xdata portSTACK_TYPE ** ) pxCurrentTCB );		\
																								\
	/* Set pxRAMStack to point to the first byte to be coped from the stack. */					\
	pxRAMStack = ( data portSTACK_TYPE * data ) configSTACK_START;								\
																								\
	/* Calculate the size of the stack we are about to copy from the current					\
	stack pointer value. */																		\
	ucStackBytes = SP - ( configSTACK_START - 1 );												\
																								\
	/* Before starting to copy the stack, store the calculated stack size so					\
	the stack can be restored when the task is resumed. */										\
	*pxXRAMStack = ucStackBytes;																\
																								\
	/* Copy each stack byte in turn.  pxXRAMStack is incremented first as we					\
	have already stored the stack size into XRAM. */											\
	while( ucStackBytes )																		\
	{																							\
		pxXRAMStack++;																			\
		*pxXRAMStack = *pxRAMStack;																\
		pxRAMStack++;																			\
		ucStackBytes--;																			\
	}																							\
}
/*-----------------------------------------------------------*/

/*
 * Macro that copies the stack of the task being resumed from XRAM into 
 * internal RAM.
 */
#define portCOPY_XRAM_TO_STACK()																\
{																								\
	/* Setup the pointers as per portCOPY_STACK_TO_XRAM(), but this time to						\
	copy the data back out of XRAM and into the stack. */										\
	pxXRAMStack = ( xdata portSTACK_TYPE * ) *( ( xdata portSTACK_TYPE ** ) pxCurrentTCB );		\
	pxRAMStack = ( data portSTACK_TYPE * data ) ( configSTACK_START - 1 );						\
																								\
	/* The first value stored in XRAM was the size of the stack - i.e. the						\
	number of bytes we need to copy back. */													\
	ucStackBytes = pxXRAMStack[ 0 ];															\
																								\
	/* Copy the required number of bytes back into the stack. */								\
	do																							\
	{																							\
		pxXRAMStack++;																			\
		pxRAMStack++;																			\
		*pxRAMStack = *pxXRAMStack;																\
		ucStackBytes--;																			\
	} while( ucStackBytes );																	\
																								\
	/* Restore the stack pointer ready to use the restored stack. */							\
	SP = ( unsigned portCHAR ) pxRAMStack;														\
}
/*-----------------------------------------------------------*/

/*
 * Macro to push the current execution context onto the stack, before the stack 
 * is moved to XRAM. 
 */
#define portSAVE_CONTEXT()																		\
{																								\
	_asm																						\
		/* Push ACC first, as when restoring the context it must be restored					\
		last (it is used to set the IE register). */											\
		push	ACC																				\
		/* Store the IE register then disable interrupts. */									\
		push	IE																				\
		clr		_EA																				\
		push	DPL																				\
		push	DPH																				\
		push	b																				\
		push	ar2																				\
		push	ar3																				\
		push	ar4																				\
		push	ar5																				\
		push	ar6																				\
		push	ar7																				\
		push	ar0																				\
		push	ar1																				\
		push	PSW																				\
	_endasm;																					\
		PSW = 0;																				\
	_asm																						\
		push	_bp																				\
	_endasm;																					\
}
/*-----------------------------------------------------------*/

/*
 * Macro that restores the execution context from the stack.  The execution 
 * context was saved into the stack before the stack was copied into XRAM.
 */
#define portRESTORE_CONTEXT()																	\
{																								\
	_asm																						\
		pop		_bp																				\
		pop		PSW																				\
		pop		ar1																				\
		pop		ar0																				\
		pop		ar7																				\
		pop		ar6																				\
		pop		ar5																				\
		pop		ar4																				\
		pop		ar3																				\
		pop		ar2																				\
		pop		b																				\
		pop		DPH																				\
		pop		DPL																				\
		/* The next byte of the stack is the IE register.  Only the global						\
		enable bit forms part of the task context.  Pop off the IE then set						\
		the global enable bit to match that of the stored IE register. */						\
		pop		ACC																				\
		JB		ACC.7,0098$																		\
		CLR		IE.7																			\