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port changes for ATMEGA162 using 8bit timer2

Posted by Nobody/Anonymous on April 13, 2007
This is a tiny contribution of myself to the freeRTOS proyect. I spent some time configuring my ATMEGA162 for working with the RTOS, using timer2. It was simple, but saves time for some developers. Well hereĀ“s the code, in case anyone need it...

/*
FreeRTOS.org V4.1.3 - Copyright (C) 2003-2006 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 as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

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 can be applied should you wish 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 of how and when the exception
can be applied.

***************************************************************************
See http://www.FreeRTOS.org for documentation, latest information, license
and contact details. Please ensure to read the configuration and relevant
port sections of the online documentation.
***************************************************************************
*/

/*

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.
*/

/*
PUSTOWKA
Changes
this port is using timer2 instead of timer1, and it is modified, for
the use with ATMEGA162. see below for further indications!

*/
#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 portCHAR ) 0x08 )
#define portPRESCALE_64( ( unsigned portCHAR ) 0x04 )
#define portCLOCK_PRESCALER( ( unsigned portLONG ) 64 )
#define portCOMPARE_MATCH_A_INTERRUPT_ENABLE( ( unsigned portCHAR ) 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 ("pushr0\n\t"\
"inr0, __SREG__\n\t"\
"cli\n\t"\
"pushr0\n\t"\
"pushr1\n\t"\
"clrr1\n\t"\
"pushr2\n\t"\
"pushr3\n\t"\
"pushr4\n\t"\
"pushr5\n\t"\
"pushr6\n\t"\
"pushr7\n\t"\
"pushr8\n\t"\
"pushr9\n\t"\
"pushr10\n\t"\
"pushr11\n\t"\
"pushr12\n\t"\
"pushr13\n\t"\
"pushr14\n\t"\
"pushr15\n\t"\
"pushr16\n\t"\
"pushr17\n\t"\
"pushr18\n\t"\
"pushr19\n\t"\
"pushr20\n\t"\
"pushr21\n\t"\
"pushr22\n\t"\
"pushr23\n\t"\
"pushr24\n\t"\
"pushr25\n\t"\
"pushr26\n\t"\
"pushr27\n\t"\
"pushr28\n\t"\
"pushr29\n\t"\
"pushr30\n\t"\
"pushr31\n\t"\
"ldsr26, pxCurrentTCB\n\t"\
"ldsr27, pxCurrentTCB + 1\n\t"\
"inr0, 0x3d\n\t"\
"stx+, r0\n\t"\
"inr0, 0x3e\n\t"\
"stx+, 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 ("ldsr26, pxCurrentTCB\n\t"\
"ldsr27, pxCurrentTCB + 1\n\t"\
"ldr28, x+\n\t"\
"out__SP_L__, r28\n\t"\
"ldr29, x+\n\t"\
"out__SP_H__, r29\n\t"\
"popr31\n\t"\
"popr30\n\t"\
"popr29\n\t"\
"popr28\n\t"\
"popr27\n\t"\
"popr26\n\t"\
"popr25\n\t"\
"popr24\n\t"\
"popr23\n\t"\
"popr22\n\t"\
"popr21\n\t"\
"popr20\n\t"\
"popr19\n\t"\
"popr18\n\t"\
"popr17\n\t"\
"popr16\n\t"\
"popr15\n\t"\
"popr14\n\t"\
"popr13\n\t"\
"popr12\n\t"\
"popr11\n\t"\
"popr10\n\t"\
"popr9\n\t"\
"popr8\n\t"\
"popr7\n\t"\
"popr6\n\t"\
"popr5\n\t"\
"popr4\n\t"\
"popr3\n\t"\
"popr2\n\t"\
"popr1\n\t"\
"popr0\n\t"\
"out__SREG__, r0\n\t"\
"popr0\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 portSHORT 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 portSHORT ) pxCode;
*pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned portSHORT ) 0x00ff );
pxTopOfStack--;

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

usAddress >>= 8;
*pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned portSHORT ) 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 )
{
/* In this port we ignore the parameter and use the configUSE_PREEMPTION
definition instead. */

/* 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 portLONG ulCompareMatch;
unsigned portCHAR ucLowByte;

/*This is a personal modification. The timer normally used is Timer 1, having 16 bits.
Timer1 is used for counting of external events on my app.
One of the consequences of changing the timer to one of 8 bits, is that the configTICK_RATE_HZ
cannot be too small compared to the configCPU_CLOCK_HZ. The relation between them follows the
ecuation:

configTICK_RATE_HZ >= configCPU_CLOCK_HZ / 16384

*/

/* Using 8bit timer 2 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 8 bits so have to scale to get our required tick rate. */
ulCompareMatch /= portCLOCK_PRESCALER; // value/64

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

/* Setup compare match value for compare match A. Interrupts are disabled
before this is called so we need not worry here. */
ucLowByte = ( unsigned portCHAR ) ( ulCompareMatch & ( unsigned portLONG ) 0xff );
OCR2 = ucLowByte;

/* Setup clock source and compare match behaviour. */
ucLowByte = portCLEAR_COUNTER_ON_MATCH | portPRESCALE_64;
TCCR2 = ucLowByte;//CTC, CLK/64

/* 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_COMPARE2(void) __attribute__ ((signal, naked));
void SIG_OUTPUT_COMPARE2(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_COMPARE2(void) __attribute__ ((signal));
void SIG_OUTPUT_COMPARE2(void)
{
vTaskIncrementTick();
}
#endif



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