📄 port.c
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/*
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
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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 portCHAR ) 0x08 )
#define portPRESCALE_64 ( ( unsigned portCHAR ) 0x03 )
#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 ( "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 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 )
{
/* 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 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 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 );
ulCompareMatch >>= 8;
ucHighByte = ( unsigned portCHAR ) ( ulCompareMatch & ( unsigned portLONG ) 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
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