FreeRTOSV7.2.0/FreeRTOS/Source/portable/GCC/ATMega323/port.c - nest-connect/1.0/freertos - Git at Google

 /*
     FreeRTOS V7.2.0 - Copyright (C) 2012 Real Time Engineers Ltd.


     ***************************************************************************
      *                                                                       *
      *    FreeRTOS tutorial books are available in pdf and paperback.        *
      *    Complete, revised, and edited pdf reference manuals are also       *
      *    available.                                                         *
      *                                                                       *
      *    Purchasing FreeRTOS documentation will not only help you, by       *
      *    ensuring you get running as quickly as possible and with an        *
      *    in-depth knowledge of how to use FreeRTOS, it will also help       *
      *    the FreeRTOS project to continue with its mission of providing     *
      *    professional grade, cross platform, de facto standard solutions    *
      *    for microcontrollers - completely free of charge!                  *
      *                                                                       *
      *    >>> See http://www.FreeRTOS.org/Documentation for details. <<<     *
      *                                                                       *
      *    Thank you for using FreeRTOS, and thank you for your support!      *
      *                                                                       *
     ***************************************************************************


     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: 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!

     ***************************************************************************
      *                                                                       *
      *    Having a problem?  Start by reading the FAQ "My application does   *
      *    not run, what could be wrong?                                      *
      *                                                                       *
      *    http://www.FreeRTOS.org/FAQHelp.html                               *
      *                                                                       *
     ***************************************************************************


     http://www.FreeRTOS.org - Documentation, training, latest information,
     license and contact details.

     http://www.FreeRTOS.org/plus - 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: http://www.OpenRTOS.com.  High Integrity Systems also
     provide a safety engineered and independently SIL3 certified version under
     the SafeRTOS brand: http://www.SafeRTOS.com.
 */

 /*

 Changes from V2.6.0

 	+ AVR port - Replaced the inb() and outb() functions with direct memory
 	  access.  This allows the port to be built with the 20050414 build of
 	  WinAVR.
 */

 #include <stdlib.h>
 #include <avr/interrupt.h>

 #include "FreeRTOS.h"
 #include "task.h"

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

 /* Start tasks with interrupts enables. */
 #define portFLAGS_INT_ENABLED					( ( portSTACK_TYPE ) 0x80 )

 /* Hardware constants for timer 1. */
 #define portCLEAR_COUNTER_ON_MATCH				( ( unsigned char ) 0x08 )
 #define portPRESCALE_64							( ( unsigned char ) 0x03 )
 #define portCLOCK_PRESCALER						( ( unsigned long ) 64 )
 #define portCOMPARE_MATCH_A_INTERRUPT_ENABLE	( ( unsigned char ) 0x10 )

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

 /* 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;

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

 /*
  * Macro to save all the general purpose registers, the save the stack pointer
  * into the TCB.
  *
  * The first thing we do is save the flags then disable interrupts.  This is to
  * guard our stack against having a context switch interrupt after we have already
  * pushed the registers onto the stack - causing the 32 registers to be on the
  * stack twice.
  *
  * r1 is set to zero as the compiler expects it to be thus, however some
  * of the math routines make use of R1.
  *
  * The interrupts will have been disabled during the call to portSAVE_CONTEXT()
  * so we need not worry about reading/writing to the stack pointer.
  */

 #define portSAVE_CONTEXT()									\
 	asm volatile (	"push	r0						\n\t"	\
 					"in		r0, __SREG__			\n\t"	\
 					"cli							\n\t"	\
 					"push	r0						\n\t"	\
 					"push	r1						\n\t"	\
 					"clr	r1						\n\t"	\
 					"push	r2						\n\t"	\
 					"push	r3						\n\t"	\
 					"push	r4						\n\t"	\
 					"push	r5						\n\t"	\
 					"push	r6						\n\t"	\
 					"push	r7						\n\t"	\
 					"push	r8						\n\t"	\
 					"push	r9						\n\t"	\
 					"push	r10						\n\t"	\
 					"push	r11						\n\t"	\
 					"push	r12						\n\t"	\
 					"push	r13						\n\t"	\
 					"push	r14						\n\t"	\
 					"push	r15						\n\t"	\
 					"push	r16						\n\t"	\
 					"push	r17						\n\t"	\
 					"push	r18						\n\t"	\
 					"push	r19						\n\t"	\
 					"push	r20						\n\t"	\
 					"push	r21						\n\t"	\
 					"push	r22						\n\t"	\
 					"push	r23						\n\t"	\
 					"push	r24						\n\t"	\
 					"push	r25						\n\t"	\
 					"push	r26						\n\t"	\
 					"push	r27						\n\t"	\
 					"push	r28						\n\t"	\
 					"push	r29						\n\t"	\
 					"push	r30						\n\t"	\
 					"push	r31						\n\t"	\
 					"lds	r26, pxCurrentTCB		\n\t"	\
 					"lds	r27, pxCurrentTCB + 1	\n\t"	\
 					"in		r0, 0x3d				\n\t"	\
 					"st		x+, r0					\n\t"	\
 					"in		r0, 0x3e				\n\t"	\
 					"st		x+, r0					\n\t"	\
 				);

 /*
  * Opposite to portSAVE_CONTEXT().  Interrupts will have been disabled during
  * the context save so we can write to the stack pointer.
  */

 #define portRESTORE_CONTEXT()								\
 	asm volatile (	"lds	r26, pxCurrentTCB		\n\t"	\
 					"lds	r27, pxCurrentTCB + 1	\n\t"	\
 					"ld		r28, x+					\n\t"	\
 					"out	__SP_L__, r28			\n\t"	\
 					"ld		r29, x+					\n\t"	\
 					"out	__SP_H__, r29			\n\t"	\
 					"pop	r31						\n\t"	\
 					"pop	r30						\n\t"	\
 					"pop	r29						\n\t"	\
 					"pop	r28						\n\t"	\
 					"pop	r27						\n\t"	\
 					"pop	r26						\n\t"	\
 					"pop	r25						\n\t"	\
 					"pop	r24						\n\t"	\
 					"pop	r23						\n\t"	\
 					"pop	r22						\n\t"	\
 					"pop	r21						\n\t"	\
 					"pop	r20						\n\t"	\
 					"pop	r19						\n\t"	\
 					"pop	r18						\n\t"	\
 					"pop	r17						\n\t"	\
 					"pop	r16						\n\t"	\
 					"pop	r15						\n\t"	\
 					"pop	r14						\n\t"	\
 					"pop	r13						\n\t"	\
 					"pop	r12						\n\t"	\
 					"pop	r11						\n\t"	\
 					"pop	r10						\n\t"	\
 					"pop	r9						\n\t"	\
 					"pop	r8						\n\t"	\
 					"pop	r7						\n\t"	\
 					"pop	r6						\n\t"	\
 					"pop	r5						\n\t"	\
 					"pop	r4						\n\t"	\
 					"pop	r3						\n\t"	\
 					"pop	r2						\n\t"	\
 					"pop	r1						\n\t"	\
 					"pop	r0						\n\t"	\
 					"out	__SREG__, r0			\n\t"	\
 					"pop	r0						\n\t"	\
 				);

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

 /*
  * Perform hardware setup to enable ticks from timer 1, compare match A.
  */
 static void prvSetupTimerInterrupt( void );
 /*-----------------------------------------------------------*/

 /*
  * See header file for description.
  */
 portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
 {
 unsigned short usAddress;

 	/* Place a few bytes of known values on the bottom of the stack.
 	This is just useful for debugging. */

 	*pxTopOfStack = 0x11;
 	pxTopOfStack--;
 	*pxTopOfStack = 0x22;
 	pxTopOfStack--;
 	*pxTopOfStack = 0x33;
 	pxTopOfStack--;

 	/* Simulate how the stack would look after a call to vPortYield() generated by
 	the compiler. */

 	/*lint -e950 -e611 -e923 Lint doesn't like this much - but nothing I can do about it. */

 	/* The start of the task code will be popped off the stack last, so place
 	it on first. */
 	usAddress = ( unsigned short ) pxCode;
 	*pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned short ) 0x00ff );
 	pxTopOfStack--;

 	usAddress >>= 8;
 	*pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned short ) 0x00ff );
 	pxTopOfStack--;

 	/* Next simulate the stack as if after a call to portSAVE_CONTEXT().
 	portSAVE_CONTEXT places the flags on the stack immediately after r0
 	to ensure the interrupts get disabled as soon as possible, and so ensuring
 	the stack use is minimal should a context switch interrupt occur. */
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x00;	/* R0 */
 	pxTopOfStack--;
 	*pxTopOfStack = portFLAGS_INT_ENABLED;
 	pxTopOfStack--;


 	/* Now the remaining registers.   The compiler expects R1 to be 0. */
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x00;	/* R1 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x02;	/* R2 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x03;	/* R3 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x04;	/* R4 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x05;	/* R5 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x06;	/* R6 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x07;	/* R7 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x08;	/* R8 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x09;	/* R9 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x10;	/* R10 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x11;	/* R11 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x12;	/* R12 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x13;	/* R13 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x14;	/* R14 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x15;	/* R15 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x16;	/* R16 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x17;	/* R17 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x18;	/* R18 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x19;	/* R19 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x20;	/* R20 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x21;	/* R21 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x22;	/* R22 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x23;	/* R23 */
 	pxTopOfStack--;

 	/* Place the parameter on the stack in the expected location. */
 	usAddress = ( unsigned short ) pvParameters;
 	*pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned short ) 0x00ff );
 	pxTopOfStack--;

 	usAddress >>= 8;
 	*pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned short ) 0x00ff );
 	pxTopOfStack--;

 	*pxTopOfStack = ( portSTACK_TYPE ) 0x26;	/* R26 X */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x27;	/* R27 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x28;	/* R28 Y */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x29;	/* R29 */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x30;	/* R30 Z */
 	pxTopOfStack--;
 	*pxTopOfStack = ( portSTACK_TYPE ) 0x031;	/* R31 */
 	pxTopOfStack--;

 	/*lint +e950 +e611 +e923 */

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

 portBASE_TYPE xPortStartScheduler( void )
 {
 	/* Setup the hardware to generate the tick. */
 	prvSetupTimerInterrupt();

 	/* Restore the context of the first task that is going to run. */
 	portRESTORE_CONTEXT();

 	/* Simulate a function call end as generated by the compiler.  We will now
 	jump to the start of the task the context of which we have just restored. */
 	asm volatile ( "ret" );

 	/* Should not get here. */
 	return pdTRUE;
 }
 /*-----------------------------------------------------------*/

 void vPortEndScheduler( void )
 {
 	/* It is unlikely that the AVR port will get stopped.  If required simply
 	disable the tick interrupt here. */
 }
 /*-----------------------------------------------------------*/

 /*
  * Manual context switch.  The first thing we do is save the registers so we
  * can use a naked attribute.
  */
 void vPortYield( void ) __attribute__ ( ( naked ) );
 void vPortYield( void )
 {
 	portSAVE_CONTEXT();
 	vTaskSwitchContext();
 	portRESTORE_CONTEXT();

 	asm volatile ( "ret" );
 }
 /*-----------------------------------------------------------*/

 /*
  * Context switch function used by the tick.  This must be identical to
  * vPortYield() from the call to vTaskSwitchContext() onwards.  The only
  * difference from vPortYield() is the tick count is incremented as the
  * call comes from the tick ISR.
  */
 void vPortYieldFromTick( void ) __attribute__ ( ( naked ) );
 void vPortYieldFromTick( void )
 {
 	portSAVE_CONTEXT();
 	vTaskIncrementTick();
 	vTaskSwitchContext();
 	portRESTORE_CONTEXT();

 	asm volatile ( "ret" );
 }
 /*-----------------------------------------------------------*/

 /*
  * Setup timer 1 compare match A to generate a tick interrupt.
  */
 static void prvSetupTimerInterrupt( void )
 {
 unsigned long ulCompareMatch;
 unsigned char ucHighByte, ucLowByte;

 	/* Using 16bit timer 1 to generate the tick.  Correct fuses must be
 	selected for the configCPU_CLOCK_HZ clock. */

 	ulCompareMatch = configCPU_CLOCK_HZ / configTICK_RATE_HZ;

 	/* We only have 16 bits so have to scale to get our required tick rate. */
 	ulCompareMatch /= portCLOCK_PRESCALER;

 	/* Adjust for correct value. */
 	ulCompareMatch -= ( unsigned long ) 1;

 	/* Setup compare match value for compare match A.  Interrupts are disabled
 	before this is called so we need not worry here. */
 	ucLowByte = ( unsigned char ) ( ulCompareMatch & ( unsigned long ) 0xff );
 	ulCompareMatch >>= 8;
 	ucHighByte = ( unsigned char ) ( ulCompareMatch & ( unsigned long ) 0xff );
 	OCR1AH = ucHighByte;
 	OCR1AL = ucLowByte;

 	/* Setup clock source and compare match behaviour. */
 	ucLowByte = portCLEAR_COUNTER_ON_MATCH | portPRESCALE_64;
 	TCCR1B = ucLowByte;

 	/* Enable the interrupt - this is okay as interrupt are currently globally
 	disabled. */
 	ucLowByte = TIMSK;
 	ucLowByte |= portCOMPARE_MATCH_A_INTERRUPT_ENABLE;
 	TIMSK = ucLowByte;
 }
 /*-----------------------------------------------------------*/

 #if configUSE_PREEMPTION == 1

 	/*
 	 * Tick ISR for preemptive scheduler.  We can use a naked attribute as
 	 * the context is saved at the start of vPortYieldFromTick().  The tick
 	 * count is incremented after the context is saved.
 	 */
 	void SIG_OUTPUT_COMPARE1A( void ) __attribute__ ( ( signal, naked ) );
 	void SIG_OUTPUT_COMPARE1A( void )
 	{
 		vPortYieldFromTick();
 		asm volatile ( "reti" );
 	}
 #else

 	/*
 	 * Tick ISR for the cooperative scheduler.  All this does is increment the
 	 * tick count.  We don't need to switch context, this can only be done by
 	 * manual calls to taskYIELD();
 	 */
 	void SIG_OUTPUT_COMPARE1A( void ) __attribute__ ( ( signal ) );
 	void SIG_OUTPUT_COMPARE1A( void )
 	{
 		vTaskIncrementTick();
 	}
 #endif
	/*
	FreeRTOS V7.2.0 - Copyright (C) 2012 Real Time Engineers Ltd.


	***************************************************************************
	* *
	* FreeRTOS tutorial books are available in pdf and paperback. *
	* Complete, revised, and edited pdf reference manuals are also *
	* available. *
	* *
	* Purchasing FreeRTOS documentation will not only help you, by *
	* ensuring you get running as quickly as possible and with an *
	* in-depth knowledge of how to use FreeRTOS, it will also help *
	* the FreeRTOS project to continue with its mission of providing *
	* professional grade, cross platform, de facto standard solutions *
	* for microcontrollers - completely free of charge! *
	* *
	* >>> See http://www.FreeRTOS.org/Documentation for details. <<< *
	* *
	* Thank you for using FreeRTOS, and thank you for your support! *
	* *
	***************************************************************************


	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: 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!

	***************************************************************************
	* *
	* Having a problem? Start by reading the FAQ "My application does *
	* not run, what could be wrong? *
	* *
	* http://www.FreeRTOS.org/FAQHelp.html *
	* *
	***************************************************************************


	http://www.FreeRTOS.org - Documentation, training, latest information,
	license and contact details.

	http://www.FreeRTOS.org/plus - 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: http://www.OpenRTOS.com. High Integrity Systems also
	provide a safety engineered and independently SIL3 certified version under
	the SafeRTOS brand: http://www.SafeRTOS.com.
	*/

	/*

	Changes from V2.6.0

	+ AVR port - Replaced the inb() and outb() functions with direct memory
	access. This allows the port to be built with the 20050414 build of
	WinAVR.
	*/

	#include <stdlib.h>
	#include <avr/interrupt.h>

	#include "FreeRTOS.h"
	#include "task.h"

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

	/* Start tasks with interrupts enables. */
	#define portFLAGS_INT_ENABLED ( ( portSTACK_TYPE ) 0x80 )

	/* Hardware constants for timer 1. */
	#define portCLEAR_COUNTER_ON_MATCH ( ( unsigned char ) 0x08 )
	#define portPRESCALE_64 ( ( unsigned char ) 0x03 )
	#define portCLOCK_PRESCALER ( ( unsigned long ) 64 )
	#define portCOMPARE_MATCH_A_INTERRUPT_ENABLE ( ( unsigned char ) 0x10 )

	/-----------------------------------------------------------/

	/* 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;

	/-----------------------------------------------------------/

	/*
	* Macro to save all the general purpose registers, the save the stack pointer
	* into the TCB.
	*
	* The first thing we do is save the flags then disable interrupts. This is to
	* guard our stack against having a context switch interrupt after we have already
	* pushed the registers onto the stack - causing the 32 registers to be on the
	* stack twice.
	*
	* r1 is set to zero as the compiler expects it to be thus, however some
	* of the math routines make use of R1.
	*
	* The interrupts will have been disabled during the call to portSAVE_CONTEXT()
	* so we need not worry about reading/writing to the stack pointer.
	*/

	#define portSAVE_CONTEXT() \
	asm volatile ( "push r0 \n\t" \
	"in r0, __SREG__ \n\t" \
	"cli \n\t" \
	"push r0 \n\t" \
	"push r1 \n\t" \
	"clr r1 \n\t" \
	"push r2 \n\t" \
	"push r3 \n\t" \
	"push r4 \n\t" \
	"push r5 \n\t" \
	"push r6 \n\t" \
	"push r7 \n\t" \
	"push r8 \n\t" \
	"push r9 \n\t" \
	"push r10 \n\t" \
	"push r11 \n\t" \
	"push r12 \n\t" \
	"push r13 \n\t" \
	"push r14 \n\t" \
	"push r15 \n\t" \
	"push r16 \n\t" \
	"push r17 \n\t" \
	"push r18 \n\t" \
	"push r19 \n\t" \
	"push r20 \n\t" \
	"push r21 \n\t" \
	"push r22 \n\t" \
	"push r23 \n\t" \
	"push r24 \n\t" \
	"push r25 \n\t" \
	"push r26 \n\t" \
	"push r27 \n\t" \
	"push r28 \n\t" \
	"push r29 \n\t" \
	"push r30 \n\t" \
	"push r31 \n\t" \
	"lds r26, pxCurrentTCB \n\t" \
	"lds r27, pxCurrentTCB + 1 \n\t" \
	"in r0, 0x3d \n\t" \
	"st x+, r0 \n\t" \
	"in r0, 0x3e \n\t" \
	"st x+, r0 \n\t" \
	);

	/*
	* Opposite to portSAVE_CONTEXT(). Interrupts will have been disabled during
	* the context save so we can write to the stack pointer.
	*/

	#define portRESTORE_CONTEXT() \
	asm volatile ( "lds r26, pxCurrentTCB \n\t" \
	"lds r27, pxCurrentTCB + 1 \n\t" \
	"ld r28, x+ \n\t" \
	"out __SP_L__, r28 \n\t" \
	"ld r29, x+ \n\t" \
	"out __SP_H__, r29 \n\t" \
	"pop r31 \n\t" \
	"pop r30 \n\t" \
	"pop r29 \n\t" \
	"pop r28 \n\t" \
	"pop r27 \n\t" \
	"pop r26 \n\t" \
	"pop r25 \n\t" \
	"pop r24 \n\t" \
	"pop r23 \n\t" \
	"pop r22 \n\t" \
	"pop r21 \n\t" \
	"pop r20 \n\t" \
	"pop r19 \n\t" \
	"pop r18 \n\t" \
	"pop r17 \n\t" \
	"pop r16 \n\t" \
	"pop r15 \n\t" \
	"pop r14 \n\t" \
	"pop r13 \n\t" \
	"pop r12 \n\t" \
	"pop r11 \n\t" \
	"pop r10 \n\t" \
	"pop r9 \n\t" \
	"pop r8 \n\t" \
	"pop r7 \n\t" \
	"pop r6 \n\t" \
	"pop r5 \n\t" \
	"pop r4 \n\t" \
	"pop r3 \n\t" \
	"pop r2 \n\t" \
	"pop r1 \n\t" \
	"pop r0 \n\t" \
	"out __SREG__, r0 \n\t" \
	"pop r0 \n\t" \
	);

	/-----------------------------------------------------------/

	/*
	* Perform hardware setup to enable ticks from timer 1, compare match A.
	*/
	static void prvSetupTimerInterrupt( void );
	/-----------------------------------------------------------/

	/*
	* See header file for description.
	*/
	portSTACK_TYPE pxPortInitialiseStack( portSTACK_TYPE pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
	{
	unsigned short usAddress;

	/* Place a few bytes of known values on the bottom of the stack.
	This is just useful for debugging. */

	*pxTopOfStack = 0x11;
	pxTopOfStack--;
	*pxTopOfStack = 0x22;
	pxTopOfStack--;
	*pxTopOfStack = 0x33;
	pxTopOfStack--;

	/* Simulate how the stack would look after a call to vPortYield() generated by
	the compiler. */

	/lint -e950 -e611 -e923 Lint doesn't like this much - but nothing I can do about it. /

	/* The start of the task code will be popped off the stack last, so place
	it on first. */
	usAddress = ( unsigned short ) pxCode;
	*pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned short ) 0x00ff );
	pxTopOfStack--;

	usAddress >>= 8;
	*pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned short ) 0x00ff );
	pxTopOfStack--;

	/* Next simulate the stack as if after a call to portSAVE_CONTEXT().
	portSAVE_CONTEXT places the flags on the stack immediately after r0
	to ensure the interrupts get disabled as soon as possible, and so ensuring
	the stack use is minimal should a context switch interrupt occur. */
	pxTopOfStack = ( portSTACK_TYPE ) 0x00; / R0 */
	pxTopOfStack--;
	*pxTopOfStack = portFLAGS_INT_ENABLED;
	pxTopOfStack--;


	/* Now the remaining registers. The compiler expects R1 to be 0. */
	pxTopOfStack = ( portSTACK_TYPE ) 0x00; / R1 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x02; / R2 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x03; / R3 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x04; / R4 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x05; / R5 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x06; / R6 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x07; / R7 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x08; / R8 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x09; / R9 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x10; / R10 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x11; / R11 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x12; / R12 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x13; / R13 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x14; / R14 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x15; / R15 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x16; / R16 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x17; / R17 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x18; / R18 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x19; / R19 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x20; / R20 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x21; / R21 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x22; / R22 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x23; / R23 */
	pxTopOfStack--;

	/* Place the parameter on the stack in the expected location. */
	usAddress = ( unsigned short ) pvParameters;
	*pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned short ) 0x00ff );
	pxTopOfStack--;

	usAddress >>= 8;
	*pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned short ) 0x00ff );
	pxTopOfStack--;

	pxTopOfStack = ( portSTACK_TYPE ) 0x26; / R26 X */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x27; / R27 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x28; / R28 Y */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x29; / R29 */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x30; / R30 Z */
	pxTopOfStack--;
	pxTopOfStack = ( portSTACK_TYPE ) 0x031; / R31 */
	pxTopOfStack--;

	/lint +e950 +e611 +e923 /

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

	portBASE_TYPE xPortStartScheduler( void )
	{
	/* Setup the hardware to generate the tick. */
	prvSetupTimerInterrupt();

	/* Restore the context of the first task that is going to run. */
	portRESTORE_CONTEXT();

	/* Simulate a function call end as generated by the compiler. We will now
	jump to the start of the task the context of which we have just restored. */
	asm volatile ( "ret" );

	/* Should not get here. */
	return pdTRUE;
	}
	/-----------------------------------------------------------/

	void vPortEndScheduler( void )
	{
	/* It is unlikely that the AVR port will get stopped. If required simply
	disable the tick interrupt here. */
	}
	/-----------------------------------------------------------/

	/*
	* Manual context switch. The first thing we do is save the registers so we
	* can use a naked attribute.
	*/
	void vPortYield( void ) __attribute__ ( ( naked ) );
	void vPortYield( void )
	{
	portSAVE_CONTEXT();
	vTaskSwitchContext();
	portRESTORE_CONTEXT();

	asm volatile ( "ret" );
	}
	/-----------------------------------------------------------/

	/*
	* Context switch function used by the tick. This must be identical to
	* vPortYield() from the call to vTaskSwitchContext() onwards. The only
	* difference from vPortYield() is the tick count is incremented as the
	* call comes from the tick ISR.
	*/
	void vPortYieldFromTick( void ) __attribute__ ( ( naked ) );
	void vPortYieldFromTick( void )
	{
	portSAVE_CONTEXT();
	vTaskIncrementTick();
	vTaskSwitchContext();
	portRESTORE_CONTEXT();

	asm volatile ( "ret" );
	}
	/-----------------------------------------------------------/

	/*
	* Setup timer 1 compare match A to generate a tick interrupt.
	*/
	static void prvSetupTimerInterrupt( void )
	{
	unsigned long ulCompareMatch;
	unsigned char ucHighByte, ucLowByte;

	/* Using 16bit timer 1 to generate the tick. Correct fuses must be
	selected for the configCPU_CLOCK_HZ clock. */

	ulCompareMatch = configCPU_CLOCK_HZ / configTICK_RATE_HZ;

	/* We only have 16 bits so have to scale to get our required tick rate. */
	ulCompareMatch /= portCLOCK_PRESCALER;

	/* Adjust for correct value. */
	ulCompareMatch -= ( unsigned long ) 1;

	/* Setup compare match value for compare match A. Interrupts are disabled
	before this is called so we need not worry here. */
	ucLowByte = ( unsigned char ) ( ulCompareMatch & ( unsigned long ) 0xff );
	ulCompareMatch >>= 8;
	ucHighByte = ( unsigned char ) ( ulCompareMatch & ( unsigned long ) 0xff );
	OCR1AH = ucHighByte;
	OCR1AL = ucLowByte;

	/* Setup clock source and compare match behaviour. */
	ucLowByte = portCLEAR_COUNTER_ON_MATCH \| portPRESCALE_64;
	TCCR1B = ucLowByte;

	/* Enable the interrupt - this is okay as interrupt are currently globally
	disabled. */
	ucLowByte = TIMSK;
	ucLowByte \|= portCOMPARE_MATCH_A_INTERRUPT_ENABLE;
	TIMSK = ucLowByte;
	}
	/-----------------------------------------------------------/

	#if configUSE_PREEMPTION == 1

	/*
	* Tick ISR for preemptive scheduler. We can use a naked attribute as
	* the context is saved at the start of vPortYieldFromTick(). The tick
	* count is incremented after the context is saved.
	*/
	void SIG_OUTPUT_COMPARE1A( void ) __attribute__ ( ( signal, naked ) );
	void SIG_OUTPUT_COMPARE1A( void )
	{
	vPortYieldFromTick();
	asm volatile ( "reti" );
	}
	#else

	/*
	* Tick ISR for the cooperative scheduler. All this does is increment the
	* tick count. We don't need to switch context, this can only be done by
	* manual calls to taskYIELD();
	*/
	void SIG_OUTPUT_COMPARE1A( void ) __attribute__ ( ( signal ) );
	void SIG_OUTPUT_COMPARE1A( void )
	{
	vTaskIncrementTick();
	}
	#endif