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jeremybenn |
/*
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FreeRTOS V6.1.1 - Copyright (C) 2011 Real Time Engineers Ltd.
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***************************************************************************
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* *
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* If you are: *
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* *
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* + New to FreeRTOS, *
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* + Wanting to learn FreeRTOS or multitasking in general quickly *
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* + Looking for basic training, *
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* + Wanting to improve your FreeRTOS skills and productivity *
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* *
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* then take a look at the FreeRTOS books - available as PDF or paperback *
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* *
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* "Using the FreeRTOS Real Time Kernel - a Practical Guide" *
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* http://www.FreeRTOS.org/Documentation *
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* *
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* A pdf reference manual is also available. Both are usually delivered *
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* to your inbox within 20 minutes to two hours when purchased between 8am *
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* and 8pm GMT (although please allow up to 24 hours in case of *
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* exceptional circumstances). Thank you for your support! *
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* *
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***************************************************************************
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This file is part of the FreeRTOS distribution.
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FreeRTOS is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License (version 2) as published by the
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Free Software Foundation AND MODIFIED BY the FreeRTOS exception.
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***NOTE*** The exception to the GPL is included to allow you to distribute
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a combined work that includes FreeRTOS without being obliged to provide the
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source code for proprietary components outside of the FreeRTOS kernel.
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FreeRTOS is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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more details. You should have received a copy of the GNU General Public
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License and the FreeRTOS license exception along with FreeRTOS; if not it
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can be viewed here: http://www.freertos.org/a00114.html and also obtained
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by writing to Richard Barry, contact details for whom are available on the
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FreeRTOS WEB site.
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1 tab == 4 spaces!
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http://www.FreeRTOS.org - Documentation, latest information, license and
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contact details.
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http://www.SafeRTOS.com - A version that is certified for use in safety
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critical systems.
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http://www.OpenRTOS.com - Commercial support, development, porting,
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licensing and training services.
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*/
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/*-----------------------------------------------------------
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* Components that can be compiled to either ARM or THUMB mode are
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* contained in port.c The ISR routines, which can only be compiled
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* to ARM mode, are contained in this file.
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*----------------------------------------------------------*/
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/*
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Changes from V2.5.2
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+ The critical section management functions have been changed. These no
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longer modify the stack and are safe to use at all optimisation levels.
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The functions are now also the same for both ARM and THUMB modes.
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Changes from V2.6.0
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+ Removed the 'static' from the definition of vNonPreemptiveTick() to
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allow the demo to link when using the cooperative scheduler.
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Changes from V3.2.4
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+ The assembler statements are now included in a single asm block rather
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than each line having its own asm block.
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*/
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/* Scheduler includes. */
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#include "FreeRTOS.h"
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/* Constants required to handle interrupts. */
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#define portTIMER_MATCH_ISR_BIT ( ( unsigned char ) 0x01 )
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#define portCLEAR_VIC_INTERRUPT ( ( unsigned long ) 0 )
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/* Constants required to handle critical sections. */
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#define portNO_CRITICAL_NESTING ( ( unsigned long ) 0 )
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volatile unsigned long ulCriticalNesting = 9999UL;
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/*-----------------------------------------------------------*/
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/* ISR to handle manual context switches (from a call to taskYIELD()). */
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void vPortYieldProcessor( void ) __attribute__((interrupt("SWI"), naked));
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/*
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* The scheduler can only be started from ARM mode, hence the inclusion of this
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* function here.
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*/
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void vPortISRStartFirstTask( void );
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/*-----------------------------------------------------------*/
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void vPortISRStartFirstTask( void )
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{
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/* Simply start the scheduler. This is included here as it can only be
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called from ARM mode. */
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portRESTORE_CONTEXT();
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}
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/*-----------------------------------------------------------*/
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/*
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* Called by portYIELD() or taskYIELD() to manually force a context switch.
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*
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* When a context switch is performed from the task level the saved task
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* context is made to look as if it occurred from within the tick ISR. This
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* way the same restore context function can be used when restoring the context
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* saved from the ISR or that saved from a call to vPortYieldProcessor.
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*/
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void vPortYieldProcessor( void )
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{
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/* Within an IRQ ISR the link register has an offset from the true return
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address, but an SWI ISR does not. Add the offset manually so the same
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ISR return code can be used in both cases. */
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__asm volatile ( "ADD LR, LR, #4" );
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/* Perform the context switch. First save the context of the current task. */
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portSAVE_CONTEXT();
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/* Find the highest priority task that is ready to run. */
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__asm volatile ( "bl vTaskSwitchContext" );
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/* Restore the context of the new task. */
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portRESTORE_CONTEXT();
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}
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/*-----------------------------------------------------------*/
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/*
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* The ISR used for the scheduler tick.
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*/
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void vTickISR( void ) __attribute__((naked));
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void vTickISR( void )
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{
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/* Save the context of the interrupted task. */
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portSAVE_CONTEXT();
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/* Increment the RTOS tick count, then look for the highest priority
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task that is ready to run. */
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__asm volatile( "bl vTaskIncrementTick" );
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#if configUSE_PREEMPTION == 1
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__asm volatile( "bl vTaskSwitchContext" );
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#endif
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/* Ready for the next interrupt. */
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T0_IR = portTIMER_MATCH_ISR_BIT;
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VICVectAddr = portCLEAR_VIC_INTERRUPT;
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/* Restore the context of the new task. */
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portRESTORE_CONTEXT();
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}
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/*-----------------------------------------------------------*/
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/*
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* The interrupt management utilities can only be called from ARM mode. When
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* THUMB_INTERWORK is defined the utilities are defined as functions here to
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* ensure a switch to ARM mode. When THUMB_INTERWORK is not defined then
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* the utilities are defined as macros in portmacro.h - as per other ports.
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*/
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#ifdef THUMB_INTERWORK
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void vPortDisableInterruptsFromThumb( void ) __attribute__ ((naked));
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void vPortEnableInterruptsFromThumb( void ) __attribute__ ((naked));
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void vPortDisableInterruptsFromThumb( void )
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{
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__asm volatile (
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"STMDB SP!, {R0} \n\t" /* Push R0. */
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"MRS R0, CPSR \n\t" /* Get CPSR. */
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"ORR R0, R0, #0xC0 \n\t" /* Disable IRQ, FIQ. */
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"MSR CPSR, R0 \n\t" /* Write back modified value. */
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"LDMIA SP!, {R0} \n\t" /* Pop R0. */
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"BX R14" ); /* Return back to thumb. */
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}
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void vPortEnableInterruptsFromThumb( void )
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{
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__asm volatile (
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"STMDB SP!, {R0} \n\t" /* Push R0. */
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"MRS R0, CPSR \n\t" /* Get CPSR. */
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"BIC R0, R0, #0xC0 \n\t" /* Enable IRQ, FIQ. */
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"MSR CPSR, R0 \n\t" /* Write back modified value. */
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"LDMIA SP!, {R0} \n\t" /* Pop R0. */
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"BX R14" ); /* Return back to thumb. */
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}
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#endif /* THUMB_INTERWORK */
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/* The code generated by the GCC compiler uses the stack in different ways at
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different optimisation levels. The interrupt flags can therefore not always
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be saved to the stack. Instead the critical section nesting level is stored
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in a variable, which is then saved as part of the stack context. */
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void vPortEnterCritical( void )
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{
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/* Disable interrupts as per portDISABLE_INTERRUPTS(); */
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__asm volatile (
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"STMDB SP!, {R0} \n\t" /* Push R0. */
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"MRS R0, CPSR \n\t" /* Get CPSR. */
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"ORR R0, R0, #0xC0 \n\t" /* Disable IRQ, FIQ. */
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"MSR CPSR, R0 \n\t" /* Write back modified value. */
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"LDMIA SP!, {R0}" ); /* Pop R0. */
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/* Now interrupts are disabled ulCriticalNesting can be accessed
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directly. Increment ulCriticalNesting to keep a count of how many times
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portENTER_CRITICAL() has been called. */
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ulCriticalNesting++;
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}
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void vPortExitCritical( void )
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{
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if( ulCriticalNesting > portNO_CRITICAL_NESTING )
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{
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/* Decrement the nesting count as we are leaving a critical section. */
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ulCriticalNesting--;
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/* If the nesting level has reached zero then interrupts should be
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re-enabled. */
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if( ulCriticalNesting == portNO_CRITICAL_NESTING )
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{
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/* Enable interrupts as per portEXIT_CRITICAL(). */
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__asm volatile (
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"STMDB SP!, {R0} \n\t" /* Push R0. */
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"MRS R0, CPSR \n\t" /* Get CPSR. */
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"BIC R0, R0, #0xC0 \n\t" /* Enable IRQ, FIQ. */
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"MSR CPSR, R0 \n\t" /* Write back modified value. */
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"LDMIA SP!, {R0}" ); /* Pop R0. */
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}
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}
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}
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