2 FreeRTOS.org V4.0.5 - Copyright (C) 2003-2006 Richard Barry.
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4 This file is part of the FreeRTOS.org distribution.
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6 FreeRTOS.org is free software; you can redistribute it and/or modify
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7 it under the terms of the GNU General Public License as published by
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8 the Free Software Foundation; either version 2 of the License, or
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9 (at your option) any later version.
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11 FreeRTOS.org is distributed in the hope that it will be useful,
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12 but WITHOUT ANY WARRANTY; without even the implied warranty of
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13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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14 GNU General Public License for more details.
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16 You should have received a copy of the GNU General Public License
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17 along with FreeRTOS.org; if not, write to the Free Software
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18 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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20 A special exception to the GPL can be applied should you wish to distribute
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21 a combined work that includes FreeRTOS.org, without being obliged to provide
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22 the source code for any proprietary components. See the licensing section
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23 of http://www.FreeRTOS.org for full details of how and when the exception
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26 ***************************************************************************
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27 See http://www.FreeRTOS.org for documentation, latest information, license
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28 and contact details. Please ensure to read the configuration and relevant
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29 port sections of the online documentation.
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30 ***************************************************************************
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36 + Call to taskYIELD() from within tick ISR has been replaced by the more
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37 efficient portSWITCH_CONTEXT().
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38 + ISR function definitions renamed to include the prv prefix.
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40 Changes from V1.2.0:
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42 + prvPortResetPIC() is now called last thing before the end of the
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43 preemptive tick routine.
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47 + Replaced the sUsingPreemption variable with the configUSE_PREEMPTION
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48 macro to be consistent with the later ports.
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52 + Add function prvSetTickFrequencyDefault() to set the DOS tick back to
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53 its proper value when the scheduler exits.
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62 #include "FreeRTOS.h"
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64 #include "portasm.h"
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66 /*-----------------------------------------------------------
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67 * Implementation of functions defined in portable.h for the industrial
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69 *----------------------------------------------------------*/
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71 /*lint -e950 Non ANSI reserved words okay in this file only. */
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73 #define portTIMER_INT_NUMBER 0x08
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75 /* Setup hardware for required tick interrupt rate. */
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76 static void prvSetTickFrequency( unsigned portLONG ulTickRateHz );
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78 /* Restore hardware to as it was prior to starting the scheduler. */
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79 static void prvExitFunction( void );
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81 /* Either chain to the DOS tick (which itself clears the PIC) or clear the PIC
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82 directly. We chain to the DOS tick as close as possible to the standard DOS
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84 static void prvPortResetPIC( void );
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86 /* The tick ISR used depends on whether the preemptive or cooperative scheduler
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88 #if configUSE_PREEMPTION == 1
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89 /* Tick service routine used by the scheduler when preemptive scheduling is
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91 static void __interrupt __far prvPreemptiveTick( void );
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93 /* Tick service routine used by the scheduler when cooperative scheduling is
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95 static void __interrupt __far prvNonPreemptiveTick( void );
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97 /* Trap routine used by taskYIELD() to manually cause a context switch. */
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98 static void __interrupt __far prvYieldProcessor( void );
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100 /* Set the tick frequency back so the floppy drive works correctly when the
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101 scheduler exits. */
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102 static void prvSetTickFrequencyDefault( void );
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104 /*lint -e956 File scopes necessary here. */
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106 /* Used to signal when to chain to the DOS tick, and when to just clear the PIC ourselves. */
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107 static portSHORT sDOSTickCounter;
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109 /* Set true when the vectors are set so the scheduler will service the tick. */
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110 static portSHORT sSchedulerRunning = pdFALSE;
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112 /* 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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113 static void ( __interrupt __far *pxOldSwitchISR )();
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115 /* 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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116 static void ( __interrupt __far *pxOldSwitchISRPlus1 )();
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118 /* Used to restore the original DOS context when the scheduler is ended. */
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119 static jmp_buf xJumpBuf;
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123 /*-----------------------------------------------------------*/
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124 portBASE_TYPE xPortStartScheduler( void )
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126 pxISR pxOriginalTickISR;
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128 /* This is called with interrupts already disabled. */
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130 /* Remember what was on the interrupts we are going to use
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131 so we can put them back later if required. */
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132 pxOldSwitchISR = _dos_getvect( portSWITCH_INT_NUMBER );
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133 pxOriginalTickISR = _dos_getvect( portTIMER_INT_NUMBER );
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134 pxOldSwitchISRPlus1 = _dos_getvect( portSWITCH_INT_NUMBER + 1 );
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136 prvSetTickFrequency( configTICK_RATE_HZ );
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138 /* Put our manual switch (yield) function on a known
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140 _dos_setvect( portSWITCH_INT_NUMBER, prvYieldProcessor );
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142 /* Put the old tick on a different interrupt number so we can
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143 call it when we want. */
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144 _dos_setvect( portSWITCH_INT_NUMBER + 1, pxOriginalTickISR );
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146 #if configUSE_PREEMPTION == 1
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148 /* Put our tick switch function on the timer interrupt. */
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149 _dos_setvect( portTIMER_INT_NUMBER, prvPreemptiveTick );
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153 /* We want the timer interrupt to just increment the tick count. */
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154 _dos_setvect( portTIMER_INT_NUMBER, prvNonPreemptiveTick );
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158 /* Setup a counter that is used to call the DOS interrupt as close
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159 to it's original frequency as can be achieved given our chosen tick
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161 sDOSTickCounter = portTICKS_PER_DOS_TICK;
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163 /* Clean up function if we want to return to DOS. */
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164 if( setjmp( xJumpBuf ) != 0 )
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167 sSchedulerRunning = pdFALSE;
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171 sSchedulerRunning = pdTRUE;
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173 /* Kick off the scheduler by setting up the context of the first task. */
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174 portFIRST_CONTEXT();
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177 return sSchedulerRunning;
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179 /*-----------------------------------------------------------*/
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181 /* The tick ISR used depends on whether the preemptive or cooperative scheduler
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183 #if configUSE_PREEMPTION == 1
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184 /* Tick service routine used by the scheduler when preemptive scheduling is
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186 static void __interrupt __far prvPreemptiveTick( void )
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188 /* Get the scheduler to update the task states following the tick. */
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189 vTaskIncrementTick();
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191 /* Switch in the context of the next task to be run. */
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192 portSWITCH_CONTEXT();
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194 /* Reset the PIC ready for the next time. */
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198 static void __interrupt __far prvNonPreemptiveTick( void )
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200 /* Same as preemptive tick, but the cooperative scheduler is being used
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201 so we don't have to switch in the context of the next task. */
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202 vTaskIncrementTick();
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206 /*-----------------------------------------------------------*/
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209 static void __interrupt __far prvYieldProcessor( void )
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211 /* Switch in the context of the next task to be run. */
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212 portSWITCH_CONTEXT();
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214 /*-----------------------------------------------------------*/
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216 static void prvPortResetPIC( void )
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218 /* We are going to call the DOS tick interrupt at as close a
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219 frequency to the normal DOS tick as possible. */
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221 /* WE SHOULD NOT DO THIS IF YIELD WAS CALLED. */
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223 if( sDOSTickCounter <= 0 )
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225 sDOSTickCounter = ( portSHORT ) portTICKS_PER_DOS_TICK;
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226 __asm{ int portSWITCH_INT_NUMBER + 1 };
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230 /* Reset the PIC as the DOS tick is not being called to
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239 /*-----------------------------------------------------------*/
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241 void vPortEndScheduler( void )
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243 /* Jump back to the processor state prior to starting the
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244 scheduler. This means we are not going to be using a
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245 task stack frame so the task can be deleted. */
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246 longjmp( xJumpBuf, 1 );
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248 /*-----------------------------------------------------------*/
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250 static void prvExitFunction( void )
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252 void ( __interrupt __far *pxOriginalTickISR )();
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254 /* Interrupts should be disabled here anyway - but no
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255 harm in making sure. */
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256 portDISABLE_INTERRUPTS();
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257 if( sSchedulerRunning == pdTRUE )
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259 /* Set the DOS tick back onto the timer ticker. */
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260 pxOriginalTickISR = _dos_getvect( portSWITCH_INT_NUMBER + 1 );
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261 _dos_setvect( portTIMER_INT_NUMBER, pxOriginalTickISR );
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262 prvSetTickFrequencyDefault();
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264 /* Put back the switch interrupt routines that was in place
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265 before the scheduler started. */
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266 _dos_setvect( portSWITCH_INT_NUMBER, pxOldSwitchISR );
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267 _dos_setvect( portSWITCH_INT_NUMBER + 1, pxOldSwitchISRPlus1 );
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269 /* The tick timer is back how DOS wants it. We can re-enable
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270 interrupts without the scheduler being called. */
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271 portENABLE_INTERRUPTS();
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273 /* This will free up all the memory used by the scheduler.
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274 exiting back to dos with INT21 AH=4CH will do this anyway so
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275 it is not necessary to call this. */
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276 vTaskCleanUpResources();
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278 /*-----------------------------------------------------------*/
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280 static void prvSetTickFrequency( unsigned portLONG ulTickRateHz )
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282 const unsigned portSHORT usPIT_MODE = ( unsigned portSHORT ) 0x43;
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283 const unsigned portSHORT usPIT0 = ( unsigned portSHORT ) 0x40;
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284 const unsigned portLONG ulPIT_CONST = ( unsigned portLONG ) 1193180;
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285 const unsigned portSHORT us8254_CTR0_MODE3 = ( unsigned portSHORT ) 0x36;
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286 unsigned portLONG ulOutput;
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288 /* Setup the 8245 to tick at the wanted frequency. */
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289 portOUTPUT_BYTE( usPIT_MODE, us8254_CTR0_MODE3 );
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290 ulOutput = ulPIT_CONST / ulTickRateHz;
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292 portOUTPUT_BYTE( usPIT0, ( unsigned portSHORT )( ulOutput & ( unsigned portLONG ) 0xff ) );
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294 portOUTPUT_BYTE( usPIT0, ( unsigned portSHORT ) ( ulOutput & ( unsigned portLONG ) 0xff ) );
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296 /*-----------------------------------------------------------*/
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298 static void prvSetTickFrequencyDefault( void )
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300 const unsigned portSHORT usPIT_MODE = ( unsigned portSHORT ) 0x43;
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301 const unsigned portSHORT usPIT0 = ( unsigned portSHORT ) 0x40;
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302 const unsigned portSHORT us8254_CTR0_MODE3 = ( unsigned portSHORT ) 0x36;
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304 portOUTPUT_BYTE( usPIT_MODE, us8254_CTR0_MODE3 );
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305 portOUTPUT_BYTE( usPIT0,0 );
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306 portOUTPUT_BYTE( usPIT0,0 );
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