text: /*
  	FreeRTOS.org V5.3.0 - 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.
  	**NOTE** The 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.  Alternative commercial
  	license and support terms are also available upon request.  See the 
  	licensing section of http://www.FreeRTOS.org for full details.
  
  	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.
  
  
  	***************************************************************************
  	*                                                                         *
  	* 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.
  */
  
  
  /*-----------------------------------------------------------
   * Components that can be compiled to either ARM or THUMB mode are
   * contained in port.c  The ISR routines, which can only be compiled
   * to ARM mode, are contained in this file.
   *----------------------------------------------------------*/
  
  /*
  	Changes from V3.2.4
  
  	+ The assembler statements are now included in a single asm block rather
  	  than each line having its own asm block.
  */
  
  /* Scheduler includes. */
  #include "FreeRTOS.h"
  #include "task.h"
  
  #include "AT91SAM7X256.h"
  
  /* Constants required to handle interrupts. */
  #define portTIMER_MATCH_ISR_BIT		( ( unsigned portCHAR ) 0x01 )
  #define portCLEAR_VIC_INTERRUPT		( ( unsigned portLONG ) 0 )
  
  /* Constants required to handle critical sections. */
  #define portNO_CRITICAL_NESTING		( ( unsigned portLONG ) 0 )
  volatile unsigned portLONG ulCriticalNesting = 9999UL;
  
  /*-----------------------------------------------------------*/
  
  /* ISR to handle manual context switches (from a call to taskYIELD()). */
  void vPortYieldProcessor( void ) __attribute__((interrupt("SWI"), naked));
  
  /* 
   * The scheduler can only be started from ARM mode, hence the inclusion of this
   * function here.
   */
  void vPortISRStartFirstTask( void );
  /*-----------------------------------------------------------*/
  
  void vPortISRStartFirstTask( void )
  {
  	/* Simply start the scheduler.  This is included here as it can only be
  	called from ARM mode. */
  	portRESTORE_CONTEXT();
  }
  /*-----------------------------------------------------------*/
  
  /*
   * Called by portYIELD() or taskYIELD() to manually force a context switch.
   *
   * When a context switch is performed from the task level the saved task 
   * context is made to look as if it occurred from within the tick ISR.  This
   * way the same restore context function can be used when restoring the context
   * saved from the ISR or that saved from a call to vPortYieldProcessor.
   */
  void vPortYieldProcessor( void )
  {
  	/* Within an IRQ ISR the link register has an offset from the true return 
  	address, but an SWI ISR does not.  Add the offset manually so the same 
  	ISR return code can be used in both cases. */
  	asm volatile ( "ADD		LR, LR, #4" );
  
  	/* Perform the context switch.  First save the context of the current task. */
  	portSAVE_CONTEXT();
  
  	/* Find the highest priority task that is ready to run. */
  	vTaskSwitchContext();
  
  	/* Restore the context of the new task. */
  	portRESTORE_CONTEXT();	
  }
  /*-----------------------------------------------------------*/
  
  /* 
   * The ISR used for the scheduler tick depends on whether the cooperative or
   * the preemptive scheduler is being used.
   */
  
  #if configUSE_PREEMPTION == 0
  
  	/* The cooperative scheduler requires a normal IRQ service routine to 
  	simply increment the system tick. */
  	void vNonPreemptiveTick( void ) __attribute__ ((interrupt ("IRQ")));
  	void vNonPreemptiveTick( void )
  	{		
  		unsigned portLONG ulDummy;
  		
  		/* Increment the tick count - which may wake some tasks but as the
  		preemptive scheduler is not being used any woken task is not given
  		processor time no matter what its priority. */
  		vTaskIncrementTick();
  		
  		/* Clear the PIT interrupt. */
  		ulDummy = AT91C_BASE_PITC->PITC_PIVR;
  		
  		/* End the interrupt in the AIC. */
  		AT91C_BASE_AIC->AIC_EOICR = ulDummy;
  	}
  
  #else
  
  	/* The preemptive scheduler is defined as "naked" as the full context is
  	saved on entry as part of the context switch. */
  	void vPreemptiveTick( void ) __attribute__((naked));
  	void vPreemptiveTick( void )
  	{
  		/* Save the context of the current task. */
  		portSAVE_CONTEXT();			
  
  		/* Increment the tick count - this may wake a task. */
  		vTaskIncrementTick();
  
  		/* Find the highest priority task that is ready to run. */
  		vTaskSwitchContext();
  		
  		/* End the interrupt in the AIC. */
  		AT91C_BASE_AIC->AIC_EOICR = AT91C_BASE_PITC->PITC_PIVR;;
  		
  		portRESTORE_CONTEXT();
  	}
  
  #endif
  /*-----------------------------------------------------------*/
  
  /*
   * The interrupt management utilities can only be called from ARM mode.  When
   * THUMB_INTERWORK is defined the utilities are defined as functions here to
   * ensure a switch to ARM mode.  When THUMB_INTERWORK is not defined then
   * the utilities are defined as macros in portmacro.h - as per other ports.
   */
  void vPortDisableInterruptsFromThumb( void ) __attribute__ ((naked));
  void vPortEnableInterruptsFromThumb( void ) __attribute__ ((naked));
  
  void vPortDisableInterruptsFromThumb( void )
  {
  	asm volatile ( 
  		"STMDB	SP!, {R0}		\n\t"	/* Push R0.									*/
  		"MRS	R0, CPSR		\n\t"	/* Get CPSR.								*/
  		"ORR	R0, R0, #0xC0	\n\t"	/* Disable IRQ, FIQ.						*/
  		"MSR	CPSR, R0		\n\t"	/* Write back modified value.				*/
  		"LDMIA	SP!, {R0}		\n\t"	/* Pop R0.									*/
  		"BX		R14" );					/* Return back to thumb.					*/
  }
  		
  void vPortEnableInterruptsFromThumb( void )
  {
  	asm volatile ( 
  		"STMDB	SP!, {R0}		\n\t"	/* Push R0.									*/	
  		"MRS	R0, CPSR		\n\t"	/* Get CPSR.								*/	
  		"BIC	R0, R0, #0xC0	\n\t"	/* Enable IRQ, FIQ.							*/	
  		"MSR	CPSR, R0		\n\t"	/* Write back modified value.				*/	
  		"LDMIA	SP!, {R0}		\n\t"	/* Pop R0.									*/
  		"BX		R14" );					/* Return back to thumb.					*/
  }
  
  
  /* The code generated by the GCC compiler uses the stack in different ways at
  different optimisation levels.  The interrupt flags can therefore not always
  be saved to the stack.  Instead the critical section nesting level is stored
  in a variable, which is then saved as part of the stack context. */
  void vPortEnterCritical( void )
  {
  	/* Disable interrupts as per portDISABLE_INTERRUPTS(); 							*/
  	asm volatile ( 
  		"STMDB	SP!, {R0}			\n\t"	/* Push R0.								*/
  		"MRS	R0, CPSR			\n\t"	/* Get CPSR.							*/
  		"ORR	R0, R0, #0xC0		\n\t"	/* Disable IRQ, FIQ.					*/
  		"MSR	CPSR, R0			\n\t"	/* Write back modified value.			*/
  		"LDMIA	SP!, {R0}" );				/* Pop R0.								*/
  
  	/* Now interrupts are disabled ulCriticalNesting can be accessed 
  	directly.  Increment ulCriticalNesting to keep a count of how many times
  	portENTER_CRITICAL() has been called. */
  	ulCriticalNesting++;
  }
  
  void vPortExitCritical( void )
  {
  	if( ulCriticalNesting > portNO_CRITICAL_NESTING )
  	{
  		/* Decrement the nesting count as we are leaving a critical section. */
  		ulCriticalNesting--;
  
  		/* If the nesting level has reached zero then interrupts should be
  		re-enabled. */
  		if( ulCriticalNesting == portNO_CRITICAL_NESTING )
  		{
  			/* Enable interrupts as per portEXIT_CRITICAL().					*/
  			asm volatile ( 
  				"STMDB	SP!, {R0}		\n\t"	/* Push R0.						*/	
  				"MRS	R0, CPSR		\n\t"	/* Get CPSR.					*/	
  				"BIC	R0, R0, #0xC0	\n\t"	/* Enable IRQ, FIQ.				*/	
  				"MSR	CPSR, R0		\n\t"	/* Write back modified value.	*/	
  				"LDMIA	SP!, {R0}" );			/* Pop R0.						*/
  		}
  	}
  }
  
  