2 FreeRTOS V7.0.1 - Copyright (C) 2011 Real Time Engineers Ltd.
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5 ***************************************************************************
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7 * FreeRTOS tutorial books are available in pdf and paperback. *
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8 * Complete, revised, and edited pdf reference manuals are also *
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11 * Purchasing FreeRTOS documentation will not only help you, by *
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12 * ensuring you get running as quickly as possible and with an *
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13 * in-depth knowledge of how to use FreeRTOS, it will also help *
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14 * the FreeRTOS project to continue with its mission of providing *
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15 * professional grade, cross platform, de facto standard solutions *
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16 * for microcontrollers - completely free of charge! *
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18 * >>> See http://www.FreeRTOS.org/Documentation for details. <<< *
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20 * Thank you for using FreeRTOS, and thank you for your support! *
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22 ***************************************************************************
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25 This file is part of the FreeRTOS distribution.
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27 FreeRTOS is free software; you can redistribute it and/or modify it under
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28 the terms of the GNU General Public License (version 2) as published by the
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29 Free Software Foundation AND MODIFIED BY the FreeRTOS exception.
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30 >>>NOTE<<< The modification to the GPL is included to allow you to
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31 distribute a combined work that includes FreeRTOS without being obliged to
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32 provide the source code for proprietary components outside of the FreeRTOS
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33 kernel. FreeRTOS is distributed in the hope that it will be useful, but
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34 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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35 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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36 more details. You should have received a copy of the GNU General Public
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37 License and the FreeRTOS license exception along with FreeRTOS; if not it
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38 can be viewed here: http://www.freertos.org/a00114.html and also obtained
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39 by writing to Richard Barry, contact details for whom are available on the
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44 http://www.FreeRTOS.org - Documentation, latest information, license and
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47 http://www.SafeRTOS.com - A version that is certified for use in safety
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50 http://www.OpenRTOS.com - Commercial support, development, porting,
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51 licensing and training services.
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57 + Call to taskYIELD() from within tick ISR has been replaced by the more
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58 efficient portSWITCH_CONTEXT().
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59 + ISR function definitions renamed to include the prv prefix.
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61 Changes from V1.2.0:
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63 + prvPortResetPIC() is now called last thing before the end of the
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64 preemptive tick routine.
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68 + Replaced the sUsingPreemption variable with the configUSE_PREEMPTION
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69 macro to be consistent with the later ports.
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73 + Add function prvSetTickFrequencyDefault() to set the DOS tick back to
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74 its proper value when the scheduler exits.
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83 #include "FreeRTOS.h"
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85 #include "portasm.h"
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87 /*-----------------------------------------------------------
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88 * Implementation of functions defined in portable.h for the industrial
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90 *----------------------------------------------------------*/
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92 /*lint -e950 Non ANSI reserved words okay in this file only. */
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94 #define portTIMER_INT_NUMBER 0x08
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96 /* Setup hardware for required tick interrupt rate. */
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97 static void prvSetTickFrequency( unsigned long ulTickRateHz );
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99 /* Restore hardware to as it was prior to starting the scheduler. */
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100 static void prvExitFunction( void );
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102 /* Either chain to the DOS tick (which itself clears the PIC) or clear the PIC
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103 directly. We chain to the DOS tick as close as possible to the standard DOS
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105 static void prvPortResetPIC( void );
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107 /* The tick ISR used depends on whether the preemptive or cooperative scheduler
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109 #if configUSE_PREEMPTION == 1
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110 /* Tick service routine used by the scheduler when preemptive scheduling is
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112 static void __interrupt __far prvPreemptiveTick( void );
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114 /* Tick service routine used by the scheduler when cooperative scheduling is
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116 static void __interrupt __far prvNonPreemptiveTick( void );
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118 /* Trap routine used by taskYIELD() to manually cause a context switch. */
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119 static void __interrupt __far prvYieldProcessor( void );
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121 /* Set the tick frequency back so the floppy drive works correctly when the
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122 scheduler exits. */
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123 static void prvSetTickFrequencyDefault( void );
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125 /*lint -e956 File scopes necessary here. */
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127 /* Used to signal when to chain to the DOS tick, and when to just clear the PIC ourselves. */
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128 static short sDOSTickCounter;
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130 /* Set true when the vectors are set so the scheduler will service the tick. */
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131 static short sSchedulerRunning = pdFALSE;
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133 /* 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(). */
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134 static void ( __interrupt __far *pxOldSwitchISR )();
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136 /* Points to the original routine installed on the vector we use to chain to the DOS tick. This is then used to restore the original routine during prvExitFunction(). */
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137 static void ( __interrupt __far *pxOldSwitchISRPlus1 )();
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139 /* Used to restore the original DOS context when the scheduler is ended. */
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140 static jmp_buf xJumpBuf;
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144 /*-----------------------------------------------------------*/
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145 portBASE_TYPE xPortStartScheduler( void )
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147 pxISR pxOriginalTickISR;
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149 /* This is called with interrupts already disabled. */
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151 /* Remember what was on the interrupts we are going to use
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152 so we can put them back later if required. */
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153 pxOldSwitchISR = _dos_getvect( portSWITCH_INT_NUMBER );
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154 pxOriginalTickISR = _dos_getvect( portTIMER_INT_NUMBER );
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155 pxOldSwitchISRPlus1 = _dos_getvect( portSWITCH_INT_NUMBER + 1 );
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157 prvSetTickFrequency( configTICK_RATE_HZ );
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159 /* Put our manual switch (yield) function on a known
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161 _dos_setvect( portSWITCH_INT_NUMBER, prvYieldProcessor );
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163 /* Put the old tick on a different interrupt number so we can
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164 call it when we want. */
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165 _dos_setvect( portSWITCH_INT_NUMBER + 1, pxOriginalTickISR );
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167 #if configUSE_PREEMPTION == 1
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169 /* Put our tick switch function on the timer interrupt. */
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170 _dos_setvect( portTIMER_INT_NUMBER, prvPreemptiveTick );
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174 /* We want the timer interrupt to just increment the tick count. */
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175 _dos_setvect( portTIMER_INT_NUMBER, prvNonPreemptiveTick );
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179 /* Setup a counter that is used to call the DOS interrupt as close
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180 to it's original frequency as can be achieved given our chosen tick
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182 sDOSTickCounter = portTICKS_PER_DOS_TICK;
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184 /* Clean up function if we want to return to DOS. */
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185 if( setjmp( xJumpBuf ) != 0 )
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188 sSchedulerRunning = pdFALSE;
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192 sSchedulerRunning = pdTRUE;
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194 /* Kick off the scheduler by setting up the context of the first task. */
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195 portFIRST_CONTEXT();
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198 return sSchedulerRunning;
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200 /*-----------------------------------------------------------*/
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202 /* The tick ISR used depends on whether the preemptive or cooperative scheduler
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204 #if configUSE_PREEMPTION == 1
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205 /* Tick service routine used by the scheduler when preemptive scheduling is
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207 static void __interrupt __far prvPreemptiveTick( void )
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209 /* Get the scheduler to update the task states following the tick. */
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210 vTaskIncrementTick();
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212 /* Switch in the context of the next task to be run. */
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213 portSWITCH_CONTEXT();
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215 /* Reset the PIC ready for the next time. */
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219 static void __interrupt __far prvNonPreemptiveTick( void )
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221 /* Same as preemptive tick, but the cooperative scheduler is being used
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222 so we don't have to switch in the context of the next task. */
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223 vTaskIncrementTick();
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227 /*-----------------------------------------------------------*/
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230 static void __interrupt __far prvYieldProcessor( void )
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232 /* Switch in the context of the next task to be run. */
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233 portSWITCH_CONTEXT();
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235 /*-----------------------------------------------------------*/
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237 static void prvPortResetPIC( void )
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239 /* We are going to call the DOS tick interrupt at as close a
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240 frequency to the normal DOS tick as possible. */
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242 /* WE SHOULD NOT DO THIS IF YIELD WAS CALLED. */
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244 if( sDOSTickCounter <= 0 )
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246 sDOSTickCounter = ( short ) portTICKS_PER_DOS_TICK;
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247 __asm{ int portSWITCH_INT_NUMBER + 1 };
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251 /* Reset the PIC as the DOS tick is not being called to
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260 /*-----------------------------------------------------------*/
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262 void vPortEndScheduler( void )
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264 /* Jump back to the processor state prior to starting the
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265 scheduler. This means we are not going to be using a
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266 task stack frame so the task can be deleted. */
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267 longjmp( xJumpBuf, 1 );
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269 /*-----------------------------------------------------------*/
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271 static void prvExitFunction( void )
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273 void ( __interrupt __far *pxOriginalTickISR )();
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275 /* Interrupts should be disabled here anyway - but no
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276 harm in making sure. */
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277 portDISABLE_INTERRUPTS();
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278 if( sSchedulerRunning == pdTRUE )
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280 /* Set the DOS tick back onto the timer ticker. */
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281 pxOriginalTickISR = _dos_getvect( portSWITCH_INT_NUMBER + 1 );
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282 _dos_setvect( portTIMER_INT_NUMBER, pxOriginalTickISR );
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283 prvSetTickFrequencyDefault();
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285 /* Put back the switch interrupt routines that was in place
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286 before the scheduler started. */
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287 _dos_setvect( portSWITCH_INT_NUMBER, pxOldSwitchISR );
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288 _dos_setvect( portSWITCH_INT_NUMBER + 1, pxOldSwitchISRPlus1 );
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290 /* The tick timer is back how DOS wants it. We can re-enable
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291 interrupts without the scheduler being called. */
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292 portENABLE_INTERRUPTS();
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294 /* This will free up all the memory used by the scheduler.
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295 exiting back to dos with INT21 AH=4CH will do this anyway so
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296 it is not necessary to call this. */
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297 vTaskCleanUpResources();
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299 /*-----------------------------------------------------------*/
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301 static void prvSetTickFrequency( unsigned long ulTickRateHz )
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303 const unsigned short usPIT_MODE = ( unsigned short ) 0x43;
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304 const unsigned short usPIT0 = ( unsigned short ) 0x40;
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305 const unsigned long ulPIT_CONST = ( unsigned long ) 1193180;
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306 const unsigned short us8254_CTR0_MODE3 = ( unsigned short ) 0x36;
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307 unsigned long ulOutput;
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309 /* Setup the 8245 to tick at the wanted frequency. */
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310 portOUTPUT_BYTE( usPIT_MODE, us8254_CTR0_MODE3 );
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311 ulOutput = ulPIT_CONST / ulTickRateHz;
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313 portOUTPUT_BYTE( usPIT0, ( unsigned short )( ulOutput & ( unsigned long ) 0xff ) );
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315 portOUTPUT_BYTE( usPIT0, ( unsigned short ) ( ulOutput & ( unsigned long ) 0xff ) );
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317 /*-----------------------------------------------------------*/
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319 static void prvSetTickFrequencyDefault( void )
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321 const unsigned short usPIT_MODE = ( unsigned short ) 0x43;
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322 const unsigned short usPIT0 = ( unsigned short ) 0x40;
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323 const unsigned short us8254_CTR0_MODE3 = ( unsigned short ) 0x36;
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325 portOUTPUT_BYTE( usPIT_MODE, us8254_CTR0_MODE3 );
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326 portOUTPUT_BYTE( usPIT0,0 );
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327 portOUTPUT_BYTE( usPIT0,0 );
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