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/* V5.2.0 - Copyright (C) 2003-2009 Richard Barry.
This file is part of the distribution. 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. 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; 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 without being obliged to provide
the source code for any proprietary components. See the licensing section
of for full details.
* *
* Get the FreeRTOS eBook! See *
* *
* 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. *
* *
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Please ensure to read the configuration and relevant port sections of the
online documentation. - Documentation, latest information, license and
contact details. - A version that is certified for use in safety
critical systems. - Commercial support, development, porting,
licensing and training services.
Changes from V1.00:
+ Call to taskYIELD() from within tick ISR has been replaced by the more
efficient portSWITCH_CONTEXT().
+ ISR function definitions renamed to include the prv prefix.
Changes from V1.2.0:
+ portRESET_PIC() is now called last thing before the end of the preemptive
tick routine.
Changes from V2.6.1
+ Replaced the sUsingPreemption variable with the configUSE_PREEMPTION
macro to be consistent with the later ports.
* Implementation of functions defined in portable.h for the Flashlite 186
* port.
#include <stdlib.h>
#include <i86.h>
#include <dos.h>
#include <setjmp.h>
#include "FreeRTOS.h"
#include "task.h"
#include "portasm.h"
/*lint -e950 Non ANSI reserved words okay in this file only. */
#define portTIMER_EOI_TYPE ( 8 )
#define portRESET_PIC() portOUTPUT_WORD( ( unsigned portSHORT ) 0xff22, portTIMER_EOI_TYPE )
#define portTIMER_INT_NUMBER 0x12
#define portTIMER_1_CONTROL_REGISTER ( ( unsigned portSHORT ) 0xff5e )
#define portTIMER_0_CONTROL_REGISTER ( ( unsigned portSHORT ) 0xff56 )
#define portTIMER_INTERRUPT_ENABLE ( ( unsigned portSHORT ) 0x2000 )
/* Setup the hardware to generate the required tick frequency. */
static void prvSetTickFrequency( unsigned portLONG ulTickRateHz );
/* Set the hardware back to the state as per before the scheduler started. */
static void prvExitFunction( void );
#if configUSE_PREEMPTION == 1
/* Tick service routine used by the scheduler when preemptive scheduling is
being used. */
static void __interrupt __far prvPreemptiveTick( void );
/* Tick service routine used by the scheduler when cooperative scheduling is
being used. */
static void __interrupt __far prvNonPreemptiveTick( void );
/* Trap routine used by taskYIELD() to manually cause a context switch. */
static void __interrupt __far prvYieldProcessor( void );
/*lint -e956 File scopes necessary here. */
/* Set true when the vectors are set so the scheduler will service the tick. */
static portSHORT sSchedulerRunning = pdFALSE;
/* Points to the original routine installed on the vector we use for manual context switches. This is then used to restore the original routine during prvExitFunction(). */
static void ( __interrupt __far *pxOldSwitchISR )();
/* Used to restore the original DOS context when the scheduler is ended. */
static jmp_buf xJumpBuf;
/*lint +e956 */
portBASE_TYPE xPortStartScheduler( void )
/* This is called with interrupts already disabled. */
/* Remember what was on the interrupts we are going to use
so we can put them back later if required. */
pxOldSwitchISR = _dos_getvect( portSWITCH_INT_NUMBER );
/* Put our manual switch (yield) function on a known
vector. */
_dos_setvect( portSWITCH_INT_NUMBER, prvYieldProcessor );
#if configUSE_PREEMPTION == 1
/* Put our tick switch function on the timer interrupt. */
_dos_setvect( portTIMER_INT_NUMBER, prvPreemptiveTick );
/* We want the timer interrupt to just increment the tick count. */
_dos_setvect( portTIMER_INT_NUMBER, prvNonPreemptiveTick );
prvSetTickFrequency( configTICK_RATE_HZ );
/* Clean up function if we want to return to DOS. */
if( setjmp( xJumpBuf ) != 0 )
sSchedulerRunning = pdFALSE;
sSchedulerRunning = pdTRUE;
/* Kick off the scheduler by setting up the context of the first task. */
return sSchedulerRunning;
/* The tick ISR used depend on whether or not the preemptive or cooperative
kernel is being used. */
#if configUSE_PREEMPTION == 1
static void __interrupt __far prvPreemptiveTick( void )
/* Get the scheduler to update the task states following the tick. */
/* Switch in the context of the next task to be run. */
/* Reset the PIC ready for the next time. */
static void __interrupt __far prvNonPreemptiveTick( void )
/* Same as preemptive tick, but the cooperative scheduler is being used
so we don't have to switch in the context of the next task. */
static void __interrupt __far prvYieldProcessor( void )
/* Switch in the context of the next task to be run. */
void vPortEndScheduler( void )
/* Jump back to the processor state prior to starting the
scheduler. This means we are not going to be using a
task stack frame so the task can be deleted. */
longjmp( xJumpBuf, 1 );
static void prvExitFunction( void )
const unsigned portSHORT usTimerDisable = 0x0000;
unsigned portSHORT usTimer0Control;
/* Interrupts should be disabled here anyway - but no
harm in making sure. */
if( sSchedulerRunning == pdTRUE )
/* Put back the switch interrupt routines that was in place
before the scheduler started. */
_dos_setvect( portSWITCH_INT_NUMBER, pxOldSwitchISR );
/* Disable the timer used for the tick to ensure the scheduler is
not called before restoring interrupts. There was previously nothing
on this timer so there is no old ISR to restore. */
portOUTPUT_WORD( portTIMER_1_CONTROL_REGISTER, usTimerDisable );
/* Restart the DOS tick. */
usTimer0Control = portINPUT_WORD( portTIMER_0_CONTROL_REGISTER );
usTimer0Control |= portTIMER_INTERRUPT_ENABLE;
portOUTPUT_WORD( portTIMER_0_CONTROL_REGISTER, usTimer0Control );
/* This will free up all the memory used by the scheduler.
exiting back to dos with INT21 AH=4CH will do this anyway so
it is not necessary to call this. */
static void prvSetTickFrequency( unsigned portLONG ulTickRateHz )
const unsigned portSHORT usMaxCountRegister = 0xff5a;
const unsigned portSHORT usTimerPriorityRegister = 0xff32;
const unsigned portSHORT usTimerEnable = 0xC000;
const unsigned portSHORT usRetrigger = 0x0001;
const unsigned portSHORT usTimerHighPriority = 0x0000;
unsigned portSHORT usTimer0Control;
/* ( CPU frequency / 4 ) / clock 2 max count [inpw( 0xff62 ) = 7] */
const unsigned portLONG ulClockFrequency = 0x7f31a0;
unsigned portLONG ulTimerCount = ulClockFrequency / ulTickRateHz;
portOUTPUT_WORD( portTIMER_1_CONTROL_REGISTER, usTimerEnable | portTIMER_INTERRUPT_ENABLE | usRetrigger );
portOUTPUT_WORD( usMaxCountRegister, ( unsigned portSHORT ) ulTimerCount );
portOUTPUT_WORD( usTimerPriorityRegister, usTimerHighPriority );
/* Stop the DOS tick - don't do this if you want to maintain a TOD clock. */
usTimer0Control = portINPUT_WORD( portTIMER_0_CONTROL_REGISTER );
usTimer0Control &= ~portTIMER_INTERRUPT_ENABLE;
portOUTPUT_WORD( portTIMER_0_CONTROL_REGISTER, usTimer0Control );
/*lint +e950 */