2 * FreeRTOS Kernel V10.3.0
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3 * Copyright (C) 2020 Amazon.com, Inc. or its affiliates. All Rights Reserved.
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5 * Permission is hereby granted, free of charge, to any person obtaining a copy of
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6 * this software and associated documentation files (the "Software"), to deal in
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7 * the Software without restriction, including without limitation the rights to
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8 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
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9 * the Software, and to permit persons to whom the Software is furnished to do so,
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10 * subject to the following conditions:
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12 * The above copyright notice and this permission notice shall be included in all
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13 * copies or substantial portions of the Software.
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15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
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17 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
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18 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
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19 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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20 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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22 * http://www.FreeRTOS.org
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23 * http://aws.amazon.com/freertos
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25 * 1 tab == 4 spaces!
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28 /*-----------------------------------------------------------
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29 * Implementation of functions defined in portable.h for the ARM CM0 port.
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30 *----------------------------------------------------------*/
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33 #include "intrinsics.h"
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35 /* Scheduler includes. */
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36 #include "FreeRTOS.h"
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39 /* Constants required to manipulate the NVIC. */
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40 #define portNVIC_SYSTICK_CTRL_REG ( * ( ( volatile uint32_t * ) 0xe000e010 ) )
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41 #define portNVIC_SYSTICK_LOAD_REG ( * ( ( volatile uint32_t * ) 0xe000e014 ) )
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42 #define portNVIC_SYSTICK_CURRENT_VALUE_REG ( * ( ( volatile uint32_t * ) 0xe000e018 ) )
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43 #define portNVIC_INT_CTRL_REG ( * ( ( volatile uint32_t * ) 0xe000ed04 ) )
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44 #define portNVIC_SYSPRI2_REG ( * ( ( volatile uint32_t *) 0xe000ed20 ) )
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45 #define portNVIC_SYSTICK_CLK_BIT ( 1UL << 2UL )
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46 #define portNVIC_SYSTICK_INT_BIT ( 1UL << 1UL )
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47 #define portNVIC_SYSTICK_ENABLE_BIT ( 1UL << 0UL )
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48 #define portNVIC_SYSTICK_COUNT_FLAG_BIT ( 1UL << 16UL )
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49 #define portMIN_INTERRUPT_PRIORITY ( 255UL )
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50 #define portNVIC_PENDSV_PRI ( portMIN_INTERRUPT_PRIORITY << 16UL )
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51 #define portNVIC_SYSTICK_PRI ( portMIN_INTERRUPT_PRIORITY << 24UL )
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53 /* Constants required to set up the initial stack. */
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54 #define portINITIAL_XPSR ( 0x01000000 )
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56 /* For backward compatibility, ensure configKERNEL_INTERRUPT_PRIORITY is
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57 defined. The value 255 should also ensure backward compatibility.
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58 FreeRTOS.org versions prior to V4.3.0 did not include this definition. */
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59 #ifndef configKERNEL_INTERRUPT_PRIORITY
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60 #define configKERNEL_INTERRUPT_PRIORITY 0
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63 /* Each task maintains its own interrupt status in the critical nesting
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65 static UBaseType_t uxCriticalNesting = 0xaaaaaaaa;
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67 /* The systick is a 24-bit counter. */
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68 #define portMAX_24_BIT_NUMBER ( 0xffffffUL )
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70 /* A fiddle factor to estimate the number of SysTick counts that would have
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71 occurred while the SysTick counter is stopped during tickless idle
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73 #ifndef portMISSED_COUNTS_FACTOR
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74 #define portMISSED_COUNTS_FACTOR ( 45UL )
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77 /* The number of SysTick increments that make up one tick period. */
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78 #if( configUSE_TICKLESS_IDLE == 1 )
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79 static uint32_t ulTimerCountsForOneTick = 0;
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80 #endif /* configUSE_TICKLESS_IDLE */
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82 /* The maximum number of tick periods that can be suppressed is limited by the
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83 24 bit resolution of the SysTick timer. */
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84 #if( configUSE_TICKLESS_IDLE == 1 )
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85 static uint32_t xMaximumPossibleSuppressedTicks = 0;
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86 #endif /* configUSE_TICKLESS_IDLE */
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88 /* Compensate for the CPU cycles that pass while the SysTick is stopped (low
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89 power functionality only. */
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90 #if( configUSE_TICKLESS_IDLE == 1 )
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91 static uint32_t ulStoppedTimerCompensation = 0;
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92 #endif /* configUSE_TICKLESS_IDLE */
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95 * Setup the timer to generate the tick interrupts. The implementation in this
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96 * file is weak to allow application writers to change the timer used to
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97 * generate the tick interrupt.
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99 #pragma weak vPortSetupTimerInterrupt
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100 void vPortSetupTimerInterrupt( void );
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103 * Exception handlers.
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105 void xPortSysTickHandler( void );
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108 * Start first task is a separate function so it can be tested in isolation.
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110 extern void vPortStartFirstTask( void );
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113 * Used to catch tasks that attempt to return from their implementing function.
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115 static void prvTaskExitError( void );
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117 /*-----------------------------------------------------------*/
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120 * See header file for description.
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122 StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )
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124 /* Simulate the stack frame as it would be created by a context switch
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126 pxTopOfStack--; /* Offset added to account for the way the MCU uses the stack on entry/exit of interrupts. */
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127 *pxTopOfStack = portINITIAL_XPSR; /* xPSR */
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129 *pxTopOfStack = ( StackType_t ) pxCode; /* PC */
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131 *pxTopOfStack = ( StackType_t ) prvTaskExitError; /* LR */
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132 pxTopOfStack -= 5; /* R12, R3, R2 and R1. */
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133 *pxTopOfStack = ( StackType_t ) pvParameters; /* R0 */
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134 pxTopOfStack -= 8; /* R11..R4. */
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136 return pxTopOfStack;
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138 /*-----------------------------------------------------------*/
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140 static void prvTaskExitError( void )
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142 /* A function that implements a task must not exit or attempt to return to
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143 its caller as there is nothing to return to. If a task wants to exit it
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144 should instead call vTaskDelete( NULL ).
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146 Artificially force an assert() to be triggered if configASSERT() is
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147 defined, then stop here so application writers can catch the error. */
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148 configASSERT( uxCriticalNesting == ~0UL );
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149 portDISABLE_INTERRUPTS();
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152 /*-----------------------------------------------------------*/
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155 * See header file for description.
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157 BaseType_t xPortStartScheduler( void )
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159 /* Make PendSV and SysTick the lowest priority interrupts. */
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160 portNVIC_SYSPRI2_REG |= portNVIC_PENDSV_PRI;
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161 portNVIC_SYSPRI2_REG |= portNVIC_SYSTICK_PRI;
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163 /* Start the timer that generates the tick ISR. Interrupts are disabled
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165 vPortSetupTimerInterrupt();
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167 /* Initialise the critical nesting count ready for the first task. */
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168 uxCriticalNesting = 0;
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170 /* Start the first task. */
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171 vPortStartFirstTask();
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173 /* Should not get here! */
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176 /*-----------------------------------------------------------*/
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178 void vPortEndScheduler( void )
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180 /* Not implemented in ports where there is nothing to return to.
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181 Artificially force an assert. */
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182 configASSERT( uxCriticalNesting == 1000UL );
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184 /*-----------------------------------------------------------*/
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186 void vPortYield( void )
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188 /* Set a PendSV to request a context switch. */
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189 portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET;
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191 /* Barriers are normally not required but do ensure the code is completely
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192 within the specified behaviour for the architecture. */
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196 /*-----------------------------------------------------------*/
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198 void vPortEnterCritical( void )
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200 portDISABLE_INTERRUPTS();
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201 uxCriticalNesting++;
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205 /*-----------------------------------------------------------*/
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207 void vPortExitCritical( void )
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209 configASSERT( uxCriticalNesting );
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210 uxCriticalNesting--;
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211 if( uxCriticalNesting == 0 )
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213 portENABLE_INTERRUPTS();
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216 /*-----------------------------------------------------------*/
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218 void xPortSysTickHandler( void )
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220 uint32_t ulPreviousMask;
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222 ulPreviousMask = portSET_INTERRUPT_MASK_FROM_ISR();
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224 /* Increment the RTOS tick. */
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225 if( xTaskIncrementTick() != pdFALSE )
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227 /* Pend a context switch. */
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228 portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET;
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231 portCLEAR_INTERRUPT_MASK_FROM_ISR( ulPreviousMask );
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233 /*-----------------------------------------------------------*/
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236 * Setup the systick timer to generate the tick interrupts at the required
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239 void vPortSetupTimerInterrupt( void )
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241 /* Calculate the constants required to configure the tick interrupt. */
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242 #if( configUSE_TICKLESS_IDLE == 1 )
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244 ulTimerCountsForOneTick = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ );
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245 xMaximumPossibleSuppressedTicks = portMAX_24_BIT_NUMBER / ulTimerCountsForOneTick;
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246 ulStoppedTimerCompensation = portMISSED_COUNTS_FACTOR;
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248 #endif /* configUSE_TICKLESS_IDLE */
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250 /* Stop and reset the SysTick. */
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251 portNVIC_SYSTICK_CTRL_REG = 0UL;
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252 portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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254 /* Configure SysTick to interrupt at the requested rate. */
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255 portNVIC_SYSTICK_LOAD_REG = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
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256 portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;
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258 /*-----------------------------------------------------------*/
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260 #if( configUSE_TICKLESS_IDLE == 1 )
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262 __weak void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
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264 uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements;
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265 TickType_t xModifiableIdleTime;
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267 /* Make sure the SysTick reload value does not overflow the counter. */
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268 if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
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270 xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
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273 /* Stop the SysTick momentarily. The time the SysTick is stopped for
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274 is accounted for as best it can be, but using the tickless mode will
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275 inevitably result in some tiny drift of the time maintained by the
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276 kernel with respect to calendar time. */
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277 portNVIC_SYSTICK_CTRL_REG &= ~portNVIC_SYSTICK_ENABLE_BIT;
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279 /* Calculate the reload value required to wait xExpectedIdleTime
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280 tick periods. -1 is used because this code will execute part way
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281 through one of the tick periods. */
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282 ulReloadValue = portNVIC_SYSTICK_CURRENT_VALUE_REG + ( ulTimerCountsForOneTick * ( xExpectedIdleTime - 1UL ) );
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283 if( ulReloadValue > ulStoppedTimerCompensation )
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285 ulReloadValue -= ulStoppedTimerCompensation;
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288 /* Enter a critical section but don't use the taskENTER_CRITICAL()
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289 method as that will mask interrupts that should exit sleep mode. */
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290 __disable_interrupt();
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294 /* If a context switch is pending or a task is waiting for the scheduler
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295 to be unsuspended then abandon the low power entry. */
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296 if( eTaskConfirmSleepModeStatus() == eAbortSleep )
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298 /* Restart from whatever is left in the count register to complete
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299 this tick period. */
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300 portNVIC_SYSTICK_LOAD_REG = portNVIC_SYSTICK_CURRENT_VALUE_REG;
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302 /* Restart SysTick. */
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303 portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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305 /* Reset the reload register to the value required for normal tick
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307 portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
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309 /* Re-enable interrupts - see comments above __disable_interrupt()
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311 __enable_interrupt();
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315 /* Set the new reload value. */
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316 portNVIC_SYSTICK_LOAD_REG = ulReloadValue;
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318 /* Clear the SysTick count flag and set the count value back to
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320 portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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322 /* Restart SysTick. */
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323 portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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325 /* Sleep until something happens. configPRE_SLEEP_PROCESSING() can
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326 set its parameter to 0 to indicate that its implementation contains
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327 its own wait for interrupt or wait for event instruction, and so wfi
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328 should not be executed again. However, the original expected idle
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329 time variable must remain unmodified, so a copy is taken. */
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330 xModifiableIdleTime = xExpectedIdleTime;
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331 configPRE_SLEEP_PROCESSING( xModifiableIdleTime );
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332 if( xModifiableIdleTime > 0 )
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338 configPOST_SLEEP_PROCESSING( xExpectedIdleTime );
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340 /* Re-enable interrupts to allow the interrupt that brought the MCU
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341 out of sleep mode to execute immediately. see comments above
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342 __disable_interrupt() call above. */
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343 __enable_interrupt();
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347 /* Disable interrupts again because the clock is about to be stopped
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348 and interrupts that execute while the clock is stopped will increase
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349 any slippage between the time maintained by the RTOS and calendar
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351 __disable_interrupt();
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355 /* Disable the SysTick clock without reading the
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356 portNVIC_SYSTICK_CTRL_REG register to ensure the
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357 portNVIC_SYSTICK_COUNT_FLAG_BIT is not cleared if it is set. Again,
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358 the time the SysTick is stopped for is accounted for as best it can
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359 be, but using the tickless mode will inevitably result in some tiny
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360 drift of the time maintained by the kernel with respect to calendar
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362 portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT );
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364 /* Determine if the SysTick clock has already counted to zero and
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365 been set back to the current reload value (the reload back being
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366 correct for the entire expected idle time) or if the SysTick is yet
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367 to count to zero (in which case an interrupt other than the SysTick
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368 must have brought the system out of sleep mode). */
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369 if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
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371 uint32_t ulCalculatedLoadValue;
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373 /* The tick interrupt is already pending, and the SysTick count
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374 reloaded with ulReloadValue. Reset the
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375 portNVIC_SYSTICK_LOAD_REG with whatever remains of this tick
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377 ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );
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379 /* Don't allow a tiny value, or values that have somehow
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380 underflowed because the post sleep hook did something
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381 that took too long. */
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382 if( ( ulCalculatedLoadValue < ulStoppedTimerCompensation ) || ( ulCalculatedLoadValue > ulTimerCountsForOneTick ) )
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384 ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL );
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387 portNVIC_SYSTICK_LOAD_REG = ulCalculatedLoadValue;
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389 /* As the pending tick will be processed as soon as this
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390 function exits, the tick value maintained by the tick is stepped
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391 forward by one less than the time spent waiting. */
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392 ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
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396 /* Something other than the tick interrupt ended the sleep.
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397 Work out how long the sleep lasted rounded to complete tick
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398 periods (not the ulReload value which accounted for part
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400 ulCompletedSysTickDecrements = ( xExpectedIdleTime * ulTimerCountsForOneTick ) - portNVIC_SYSTICK_CURRENT_VALUE_REG ;
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402 /* How many complete tick periods passed while the processor
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404 ulCompleteTickPeriods = ulCompletedSysTickDecrements / ulTimerCountsForOneTick;
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406 /* The reload value is set to whatever fraction of a single tick
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408 portNVIC_SYSTICK_LOAD_REG = ( ( ulCompleteTickPeriods + 1UL ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
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411 /* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG
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412 again, then set portNVIC_SYSTICK_LOAD_REG back to its standard
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414 portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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415 portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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416 vTaskStepTick( ulCompleteTickPeriods );
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417 portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
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419 /* Exit with interrpts enabled. */
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420 __enable_interrupt();
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424 #endif /* configUSE_TICKLESS_IDLE */
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