2 FreeRTOS.org V4.7.1 - Copyright (C) 2003-2008 Richard Barry.
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18 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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26 ***************************************************************************
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28 Please ensure to read the configuration and relevant port sections of the
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29 online documentation.
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31 +++ http://www.FreeRTOS.org +++
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32 Documentation, latest information, license and contact details.
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34 +++ http://www.SafeRTOS.com +++
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35 A version that is certified for use in safety critical systems.
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37 +++ http://www.OpenRTOS.com +++
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38 Commercial support, development, porting, licensing and training services.
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40 ***************************************************************************
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47 + AVR port - Replaced the inb() and outb() functions with direct memory
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48 access. This allows the port to be built with the 20050414 build of
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53 #include <avr/interrupt.h>
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55 #include "FreeRTOS.h"
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58 /*-----------------------------------------------------------
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59 * Implementation of functions defined in portable.h for the AVR port.
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60 *----------------------------------------------------------*/
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62 /* Start tasks with interrupts enables. */
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63 #define portFLAGS_INT_ENABLED ( ( portSTACK_TYPE ) 0x80 )
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65 /* Hardware constants for timer 1. */
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66 #define portCLEAR_COUNTER_ON_MATCH ( ( unsigned portCHAR ) 0x08 )
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67 #define portPRESCALE_64 ( ( unsigned portCHAR ) 0x03 )
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68 #define portCLOCK_PRESCALER ( ( unsigned portLONG ) 64 )
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69 #define portCOMPARE_MATCH_A_INTERRUPT_ENABLE ( ( unsigned portCHAR ) 0x10 )
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71 /*-----------------------------------------------------------*/
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73 /* We require the address of the pxCurrentTCB variable, but don't want to know
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74 any details of its type. */
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75 typedef void tskTCB;
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76 extern volatile tskTCB * volatile pxCurrentTCB;
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78 /*-----------------------------------------------------------*/
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81 * Macro to save all the general purpose registers, the save the stack pointer
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84 * The first thing we do is save the flags then disable interrupts. This is to
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85 * guard our stack against having a context switch interrupt after we have already
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86 * pushed the registers onto the stack - causing the 32 registers to be on the
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89 * r1 is set to zero as the compiler expects it to be thus, however some
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90 * of the math routines make use of R1.
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92 * The interrupts will have been disabled during the call to portSAVE_CONTEXT()
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93 * so we need not worry about reading/writing to the stack pointer.
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96 #define portSAVE_CONTEXT() \
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97 asm volatile ( "push r0 \n\t" \
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98 "in r0, __SREG__ \n\t" \
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133 "lds r26, pxCurrentTCB \n\t" \
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134 "lds r27, pxCurrentTCB + 1 \n\t" \
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135 "in r0, 0x3d \n\t" \
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137 "in r0, 0x3e \n\t" \
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142 * Opposite to portSAVE_CONTEXT(). Interrupts will have been disabled during
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143 * the context save so we can write to the stack pointer.
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146 #define portRESTORE_CONTEXT() \
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147 asm volatile ( "lds r26, pxCurrentTCB \n\t" \
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148 "lds r27, pxCurrentTCB + 1 \n\t" \
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149 "ld r28, x+ \n\t" \
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150 "out __SP_L__, r28 \n\t" \
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151 "ld r29, x+ \n\t" \
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152 "out __SP_H__, r29 \n\t" \
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185 "out __SREG__, r0 \n\t" \
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189 /*-----------------------------------------------------------*/
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192 * Perform hardware setup to enable ticks from timer 1, compare match A.
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194 static void prvSetupTimerInterrupt( void );
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195 /*-----------------------------------------------------------*/
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198 * See header file for description.
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200 portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
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202 unsigned portSHORT usAddress;
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204 /* Place a few bytes of known values on the bottom of the stack.
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205 This is just useful for debugging. */
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207 *pxTopOfStack = 0x11;
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209 *pxTopOfStack = 0x22;
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211 *pxTopOfStack = 0x33;
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214 /* Simulate how the stack would look after a call to vPortYield() generated by
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217 /*lint -e950 -e611 -e923 Lint doesn't like this much - but nothing I can do about it. */
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219 /* The start of the task code will be popped off the stack last, so place
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221 usAddress = ( unsigned portSHORT ) pxCode;
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222 *pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned portSHORT ) 0x00ff );
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226 *pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned portSHORT ) 0x00ff );
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229 /* Next simulate the stack as if after a call to portSAVE_CONTEXT().
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230 portSAVE_CONTEXT places the flags on the stack immediately after r0
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231 to ensure the interrupts get disabled as soon as possible, and so ensuring
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232 the stack use is minimal should a context switch interrupt occur. */
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233 *pxTopOfStack = ( portSTACK_TYPE ) 0x00; /* R0 */
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235 *pxTopOfStack = portFLAGS_INT_ENABLED;
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239 /* Now the remaining registers. The compiler expects R1 to be 0. */
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240 *pxTopOfStack = ( portSTACK_TYPE ) 0x00; /* R1 */
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242 *pxTopOfStack = ( portSTACK_TYPE ) 0x02; /* R2 */
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244 *pxTopOfStack = ( portSTACK_TYPE ) 0x03; /* R3 */
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246 *pxTopOfStack = ( portSTACK_TYPE ) 0x04; /* R4 */
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248 *pxTopOfStack = ( portSTACK_TYPE ) 0x05; /* R5 */
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250 *pxTopOfStack = ( portSTACK_TYPE ) 0x06; /* R6 */
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252 *pxTopOfStack = ( portSTACK_TYPE ) 0x07; /* R7 */
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254 *pxTopOfStack = ( portSTACK_TYPE ) 0x08; /* R8 */
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256 *pxTopOfStack = ( portSTACK_TYPE ) 0x09; /* R9 */
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258 *pxTopOfStack = ( portSTACK_TYPE ) 0x10; /* R10 */
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260 *pxTopOfStack = ( portSTACK_TYPE ) 0x11; /* R11 */
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262 *pxTopOfStack = ( portSTACK_TYPE ) 0x12; /* R12 */
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264 *pxTopOfStack = ( portSTACK_TYPE ) 0x13; /* R13 */
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266 *pxTopOfStack = ( portSTACK_TYPE ) 0x14; /* R14 */
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268 *pxTopOfStack = ( portSTACK_TYPE ) 0x15; /* R15 */
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270 *pxTopOfStack = ( portSTACK_TYPE ) 0x16; /* R16 */
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272 *pxTopOfStack = ( portSTACK_TYPE ) 0x17; /* R17 */
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274 *pxTopOfStack = ( portSTACK_TYPE ) 0x18; /* R18 */
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276 *pxTopOfStack = ( portSTACK_TYPE ) 0x19; /* R19 */
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278 *pxTopOfStack = ( portSTACK_TYPE ) 0x20; /* R20 */
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280 *pxTopOfStack = ( portSTACK_TYPE ) 0x21; /* R21 */
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282 *pxTopOfStack = ( portSTACK_TYPE ) 0x22; /* R22 */
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284 *pxTopOfStack = ( portSTACK_TYPE ) 0x23; /* R23 */
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287 /* Place the parameter on the stack in the expected location. */
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288 usAddress = ( unsigned portSHORT ) pvParameters;
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289 *pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned portSHORT ) 0x00ff );
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293 *pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned portSHORT ) 0x00ff );
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296 *pxTopOfStack = ( portSTACK_TYPE ) 0x26; /* R26 X */
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298 *pxTopOfStack = ( portSTACK_TYPE ) 0x27; /* R27 */
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300 *pxTopOfStack = ( portSTACK_TYPE ) 0x28; /* R28 Y */
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302 *pxTopOfStack = ( portSTACK_TYPE ) 0x29; /* R29 */
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304 *pxTopOfStack = ( portSTACK_TYPE ) 0x30; /* R30 Z */
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306 *pxTopOfStack = ( portSTACK_TYPE ) 0x031; /* R31 */
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309 /*lint +e950 +e611 +e923 */
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311 return pxTopOfStack;
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313 /*-----------------------------------------------------------*/
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315 portBASE_TYPE xPortStartScheduler( void )
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317 /* Setup the hardware to generate the tick. */
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318 prvSetupTimerInterrupt();
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320 /* Restore the context of the first task that is going to run. */
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321 portRESTORE_CONTEXT();
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323 /* Simulate a function call end as generated by the compiler. We will now
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324 jump to the start of the task the context of which we have just restored. */
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325 asm volatile ( "ret" );
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327 /* Should not get here. */
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330 /*-----------------------------------------------------------*/
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332 void vPortEndScheduler( void )
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334 /* It is unlikely that the AVR port will get stopped. If required simply
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335 disable the tick interrupt here. */
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337 /*-----------------------------------------------------------*/
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340 * Manual context switch. The first thing we do is save the registers so we
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341 * can use a naked attribute.
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343 void vPortYield( void ) __attribute__ ( ( naked ) );
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344 void vPortYield( void )
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346 portSAVE_CONTEXT();
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347 vTaskSwitchContext();
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348 portRESTORE_CONTEXT();
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350 asm volatile ( "ret" );
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352 /*-----------------------------------------------------------*/
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355 * Context switch function used by the tick. This must be identical to
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356 * vPortYield() from the call to vTaskSwitchContext() onwards. The only
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357 * difference from vPortYield() is the tick count is incremented as the
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358 * call comes from the tick ISR.
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360 void vPortYieldFromTick( void ) __attribute__ ( ( naked ) );
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361 void vPortYieldFromTick( void )
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363 portSAVE_CONTEXT();
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364 vTaskIncrementTick();
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365 vTaskSwitchContext();
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366 portRESTORE_CONTEXT();
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368 asm volatile ( "ret" );
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370 /*-----------------------------------------------------------*/
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373 * Setup timer 1 compare match A to generate a tick interrupt.
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375 static void prvSetupTimerInterrupt( void )
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377 unsigned portLONG ulCompareMatch;
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378 unsigned portCHAR ucHighByte, ucLowByte;
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380 /* Using 16bit timer 1 to generate the tick. Correct fuses must be
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381 selected for the configCPU_CLOCK_HZ clock. */
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383 ulCompareMatch = configCPU_CLOCK_HZ / configTICK_RATE_HZ;
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385 /* We only have 16 bits so have to scale to get our required tick rate. */
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386 ulCompareMatch /= portCLOCK_PRESCALER;
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388 /* Adjust for correct value. */
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389 ulCompareMatch -= ( unsigned portLONG ) 1;
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391 /* Setup compare match value for compare match A. Interrupts are disabled
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392 before this is called so we need not worry here. */
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393 ucLowByte = ( unsigned portCHAR ) ( ulCompareMatch & ( unsigned portLONG ) 0xff );
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394 ulCompareMatch >>= 8;
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395 ucHighByte = ( unsigned portCHAR ) ( ulCompareMatch & ( unsigned portLONG ) 0xff );
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396 OCR1AH = ucHighByte;
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397 OCR1AL = ucLowByte;
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399 /* Setup clock source and compare match behaviour. */
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400 ucLowByte = portCLEAR_COUNTER_ON_MATCH | portPRESCALE_64;
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401 TCCR1B = ucLowByte;
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403 /* Enable the interrupt - this is okay as interrupt are currently globally
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406 ucLowByte |= portCOMPARE_MATCH_A_INTERRUPT_ENABLE;
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409 /*-----------------------------------------------------------*/
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411 #if configUSE_PREEMPTION == 1
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414 * Tick ISR for preemptive scheduler. We can use a naked attribute as
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415 * the context is saved at the start of vPortYieldFromTick(). The tick
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416 * count is incremented after the context is saved.
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418 void SIG_OUTPUT_COMPARE1A( void ) __attribute__ ( ( signal, naked ) );
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419 void SIG_OUTPUT_COMPARE1A( void )
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421 vPortYieldFromTick();
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422 asm volatile ( "reti" );
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427 * Tick ISR for the cooperative scheduler. All this does is increment the
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428 * tick count. We don't need to switch context, this can only be done by
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429 * manual calls to taskYIELD();
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431 void SIG_OUTPUT_COMPARE1A( void ) __attribute__ ( ( signal ) );
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432 void SIG_OUTPUT_COMPARE1A( void )
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434 vTaskIncrementTick();
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