port.c

/*
    FreeRTOS V7.1.0 - Copyright (C) 2011 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.
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*/

/* 

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 ) (1<<WGM12) )
#define portPRESCALE_64							( ( unsigned char ) ((1<<CS11)|(1<<CS10)) )
#define portCLOCK_PRESCALER						( ( unsigned long ) 64 )
#define portCOMPARE_MATCH_A_INTERRUPT_ENABLE	( ( unsigned char ) (1<<OCIE1A) )

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

/* 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 = TIMSK1;
	ucLowByte |= portCOMPARE_MATCH_A_INTERRUPT_ENABLE;
	TIMSK1 = 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 TIMER1_COMPA_vect( void ) __attribute__ ( ( signal, naked ) );
	void TIMER1_COMPA_vect( 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 TIMER1_COMPA_vect( void ) __attribute__ ( ( signal ) );
	void TIMER1_COMPA_vect( void )
	{
		vTaskIncrementTick();
	}
#endif