2 * FreeRTOS Kernel V10.2.1
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3 * Copyright (C) 2019 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 CM4F port.
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30 *----------------------------------------------------------*/
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32 /* Scheduler includes. */
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33 #include "FreeRTOS.h"
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36 #if( configMAX_SYSCALL_INTERRUPT_PRIORITY == 0 )
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37 #error configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to 0. See http://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html
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40 #ifndef configSYSTICK_CLOCK_HZ
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41 #define configSYSTICK_CLOCK_HZ configCPU_CLOCK_HZ
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42 /* Ensure the SysTick is clocked at the same frequency as the core. */
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43 #define portNVIC_SYSTICK_CLK_BIT ( 1UL << 2UL )
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45 /* The way the SysTick is clocked is not modified in case it is not the same
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47 #define portNVIC_SYSTICK_CLK_BIT ( 0 )
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50 /* Constants required to manipulate the core. Registers first... */
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51 #define portNVIC_SYSTICK_CTRL_REG ( * ( ( volatile uint32_t * ) 0xe000e010 ) )
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52 #define portNVIC_SYSTICK_LOAD_REG ( * ( ( volatile uint32_t * ) 0xe000e014 ) )
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53 #define portNVIC_SYSTICK_CURRENT_VALUE_REG ( * ( ( volatile uint32_t * ) 0xe000e018 ) )
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54 #define portNVIC_SYSPRI2_REG ( * ( ( volatile uint32_t * ) 0xe000ed20 ) )
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55 /* ...then bits in the registers. */
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56 #define portNVIC_SYSTICK_INT_BIT ( 1UL << 1UL )
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57 #define portNVIC_SYSTICK_ENABLE_BIT ( 1UL << 0UL )
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58 #define portNVIC_SYSTICK_COUNT_FLAG_BIT ( 1UL << 16UL )
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59 #define portNVIC_PENDSVCLEAR_BIT ( 1UL << 27UL )
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60 #define portNVIC_PEND_SYSTICK_CLEAR_BIT ( 1UL << 25UL )
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62 #define portNVIC_PENDSV_PRI ( ( ( uint32_t ) configKERNEL_INTERRUPT_PRIORITY ) << 16UL )
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63 #define portNVIC_SYSTICK_PRI ( ( ( uint32_t ) configKERNEL_INTERRUPT_PRIORITY ) << 24UL )
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65 /* Constants required to check the validity of an interrupt priority. */
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66 #define portFIRST_USER_INTERRUPT_NUMBER ( 16 )
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67 #define portNVIC_IP_REGISTERS_OFFSET_16 ( 0xE000E3F0 )
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68 #define portAIRCR_REG ( * ( ( volatile uint32_t * ) 0xE000ED0C ) )
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69 #define portMAX_8_BIT_VALUE ( ( uint8_t ) 0xff )
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70 #define portTOP_BIT_OF_BYTE ( ( uint8_t ) 0x80 )
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71 #define portMAX_PRIGROUP_BITS ( ( uint8_t ) 7 )
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72 #define portPRIORITY_GROUP_MASK ( 0x07UL << 8UL )
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73 #define portPRIGROUP_SHIFT ( 8UL )
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75 /* Masks off all bits but the VECTACTIVE bits in the ICSR register. */
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76 #define portVECTACTIVE_MASK ( 0xFFUL )
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78 /* Constants required to set up the initial stack. */
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79 #define portINITIAL_XPSR ( 0x01000000 )
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81 /* The systick is a 24-bit counter. */
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82 #define portMAX_24_BIT_NUMBER ( 0xffffffUL )
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84 /* A fiddle factor to estimate the number of SysTick counts that would have
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85 occurred while the SysTick counter is stopped during tickless idle
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87 #define portMISSED_COUNTS_FACTOR ( 45UL )
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89 /* For strict compliance with the Cortex-M spec the task start address should
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90 have bit-0 clear, as it is loaded into the PC on exit from an ISR. */
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91 #define portSTART_ADDRESS_MASK ( ( StackType_t ) 0xfffffffeUL )
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94 * Setup the timer to generate the tick interrupts. The implementation in this
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95 * file is weak to allow application writers to change the timer used to
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96 * generate the tick interrupt.
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98 void vPortSetupTimerInterrupt( void );
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101 * Exception handlers.
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103 void xPortSysTickHandler( void );
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106 * Start first task is a separate function so it can be tested in isolation.
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108 extern void vPortStartFirstTask( void );
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111 * Used to catch tasks that attempt to return from their implementing function.
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113 static void prvTaskExitError( void );
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115 /*-----------------------------------------------------------*/
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117 /* Required to allow portasm.asm access the configMAX_SYSCALL_INTERRUPT_PRIORITY
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119 const uint32_t ulMaxSyscallInterruptPriority = configMAX_SYSCALL_INTERRUPT_PRIORITY;
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121 /* Each task maintains its own interrupt status in the critical nesting
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123 static UBaseType_t uxCriticalNesting = 0xaaaaaaaa;
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126 * The number of SysTick increments that make up one tick period.
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128 #if( configUSE_TICKLESS_IDLE == 1 )
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129 static uint32_t ulTimerCountsForOneTick = 0;
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130 #endif /* configUSE_TICKLESS_IDLE */
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133 * The maximum number of tick periods that can be suppressed is limited by the
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134 * 24 bit resolution of the SysTick timer.
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136 #if( configUSE_TICKLESS_IDLE == 1 )
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137 static uint32_t xMaximumPossibleSuppressedTicks = 0;
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138 #endif /* configUSE_TICKLESS_IDLE */
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141 * Compensate for the CPU cycles that pass while the SysTick is stopped (low
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142 * power functionality only.
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144 #if( configUSE_TICKLESS_IDLE == 1 )
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145 static uint32_t ulStoppedTimerCompensation = 0;
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146 #endif /* configUSE_TICKLESS_IDLE */
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149 * Used by the portASSERT_IF_INTERRUPT_PRIORITY_INVALID() macro to ensure
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150 * FreeRTOS API functions are not called from interrupts that have been assigned
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151 * a priority above configMAX_SYSCALL_INTERRUPT_PRIORITY.
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153 #if ( configASSERT_DEFINED == 1 )
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154 static uint8_t ucMaxSysCallPriority = 0;
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155 static uint32_t ulMaxPRIGROUPValue = 0;
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156 static const volatile uint8_t * const pcInterruptPriorityRegisters = ( uint8_t * ) portNVIC_IP_REGISTERS_OFFSET_16;
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157 #endif /* configASSERT_DEFINED */
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159 /*-----------------------------------------------------------*/
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162 * See header file for description.
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164 StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
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165 TaskFunction_t pxCode,
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166 void * pvParameters )
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168 /* Simulate the stack frame as it would be created by a context switch
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171 /* Offset added to account for the way the MCU uses the stack on entry/exit
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172 of interrupts, and to ensure alignment. */
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175 *pxTopOfStack = portINITIAL_XPSR; /* xPSR */
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177 *pxTopOfStack = ( ( StackType_t ) pxCode ) & portSTART_ADDRESS_MASK; /* PC */
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179 *pxTopOfStack = ( StackType_t ) prvTaskExitError; /* LR */
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181 /* Save code space by skipping register initialisation. */
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182 pxTopOfStack -= 5; /* R12, R3, R2 and R1. */
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183 *pxTopOfStack = ( StackType_t ) pvParameters; /* R0 */
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185 pxTopOfStack -= 8; /* R11, R10, R9, R8, R7, R6, R5 and R4. */
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187 return pxTopOfStack;
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189 /*-----------------------------------------------------------*/
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191 static void prvTaskExitError( void )
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193 /* A function that implements a task must not exit or attempt to return to
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194 its caller as there is nothing to return to. If a task wants to exit it
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195 should instead call vTaskDelete( NULL ).
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197 Artificially force an assert() to be triggered if configASSERT() is
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198 defined, then stop here so application writers can catch the error. */
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199 configASSERT( uxCriticalNesting == ~0UL );
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200 portDISABLE_INTERRUPTS();
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203 /*-----------------------------------------------------------*/
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206 * See header file for description.
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208 BaseType_t xPortStartScheduler( void )
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210 #if( configASSERT_DEFINED == 1 )
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212 volatile uint32_t ulOriginalPriority;
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213 volatile uint8_t * const pucFirstUserPriorityRegister = ( uint8_t * ) ( portNVIC_IP_REGISTERS_OFFSET_16 + portFIRST_USER_INTERRUPT_NUMBER );
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214 volatile uint8_t ucMaxPriorityValue;
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216 /* Determine the maximum priority from which ISR safe FreeRTOS API
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217 functions can be called. ISR safe functions are those that end in
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218 "FromISR". FreeRTOS maintains separate thread and ISR API functions to
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219 ensure interrupt entry is as fast and simple as possible.
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221 Save the interrupt priority value that is about to be clobbered. */
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222 ulOriginalPriority = *pucFirstUserPriorityRegister;
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224 /* Determine the number of priority bits available. First write to all
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226 *pucFirstUserPriorityRegister = portMAX_8_BIT_VALUE;
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228 /* Read the value back to see how many bits stuck. */
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229 ucMaxPriorityValue = *pucFirstUserPriorityRegister;
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231 /* Use the same mask on the maximum system call priority. */
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232 ucMaxSysCallPriority = configMAX_SYSCALL_INTERRUPT_PRIORITY & ucMaxPriorityValue;
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234 /* Calculate the maximum acceptable priority group value for the number
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235 of bits read back. */
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236 ulMaxPRIGROUPValue = portMAX_PRIGROUP_BITS;
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237 while( ( ucMaxPriorityValue & portTOP_BIT_OF_BYTE ) == portTOP_BIT_OF_BYTE )
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239 ulMaxPRIGROUPValue--;
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240 ucMaxPriorityValue <<= ( uint8_t ) 0x01;
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243 #ifdef __NVIC_PRIO_BITS
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245 /* Check the CMSIS configuration that defines the number of
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246 priority bits matches the number of priority bits actually queried
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247 from the hardware. */
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248 configASSERT( ( portMAX_PRIGROUP_BITS - ulMaxPRIGROUPValue ) == __NVIC_PRIO_BITS );
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252 #ifdef configPRIO_BITS
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254 /* Check the FreeRTOS configuration that defines the number of
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255 priority bits matches the number of priority bits actually queried
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256 from the hardware. */
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257 configASSERT( ( portMAX_PRIGROUP_BITS - ulMaxPRIGROUPValue ) == configPRIO_BITS );
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261 /* Shift the priority group value back to its position within the AIRCR
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263 ulMaxPRIGROUPValue <<= portPRIGROUP_SHIFT;
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264 ulMaxPRIGROUPValue &= portPRIORITY_GROUP_MASK;
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266 /* Restore the clobbered interrupt priority register to its original
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268 *pucFirstUserPriorityRegister = ulOriginalPriority;
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270 #endif /* conifgASSERT_DEFINED */
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272 /* Make PendSV and SysTick the lowest priority interrupts. */
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273 portNVIC_SYSPRI2_REG |= portNVIC_PENDSV_PRI;
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274 portNVIC_SYSPRI2_REG |= portNVIC_SYSTICK_PRI;
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276 /* Start the timer that generates the tick ISR. Interrupts are disabled
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278 vPortSetupTimerInterrupt();
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280 /* Initialise the critical nesting count ready for the first task. */
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281 uxCriticalNesting = 0;
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283 /* Start the first task. */
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284 vPortStartFirstTask();
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286 /* Should not get here! */
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289 /*-----------------------------------------------------------*/
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291 void vPortEndScheduler( void )
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293 /* Not implemented in ports where there is nothing to return to.
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294 Artificially force an assert. */
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295 configASSERT( uxCriticalNesting == 1000UL );
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297 /*-----------------------------------------------------------*/
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299 void vPortEnterCritical( void )
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301 portDISABLE_INTERRUPTS();
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302 uxCriticalNesting++;
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304 /* This is not the interrupt safe version of the enter critical function so
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305 assert() if it is being called from an interrupt context. Only API
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306 functions that end in "FromISR" can be used in an interrupt. Only assert if
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307 the critical nesting count is 1 to protect against recursive calls if the
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308 assert function also uses a critical section. */
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309 if( uxCriticalNesting == 1 )
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311 configASSERT( ( portNVIC_INT_CTRL_REG & portVECTACTIVE_MASK ) == 0 );
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314 /*-----------------------------------------------------------*/
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316 void vPortExitCritical( void )
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318 configASSERT( uxCriticalNesting );
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319 uxCriticalNesting--;
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320 if( uxCriticalNesting == 0 )
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322 portENABLE_INTERRUPTS();
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325 /*-----------------------------------------------------------*/
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327 void xPortSysTickHandler( void )
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329 /* The SysTick runs at the lowest interrupt priority, so when this interrupt
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330 executes all interrupts must be unmasked. There is therefore no need to
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331 save and then restore the interrupt mask value as its value is already
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333 ( void ) portSET_INTERRUPT_MASK_FROM_ISR();
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335 /* Increment the RTOS tick. */
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336 if( xTaskIncrementTick() != pdFALSE )
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338 /* A context switch is required. Context switching is performed in
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339 the PendSV interrupt. Pend the PendSV interrupt. */
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340 portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;
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343 portCLEAR_INTERRUPT_MASK_FROM_ISR( 0 );
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345 /*-----------------------------------------------------------*/
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347 #if( configUSE_TICKLESS_IDLE == 1 )
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349 #pragma WEAK( vPortSuppressTicksAndSleep )
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350 void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
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352 uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements;
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353 TickType_t xModifiableIdleTime;
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355 /* Make sure the SysTick reload value does not overflow the counter. */
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356 if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
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358 xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
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361 /* Stop the SysTick momentarily. The time the SysTick is stopped for
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362 is accounted for as best it can be, but using the tickless mode will
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363 inevitably result in some tiny drift of the time maintained by the
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364 kernel with respect to calendar time. */
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365 portNVIC_SYSTICK_CTRL_REG &= ~portNVIC_SYSTICK_ENABLE_BIT;
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367 /* Calculate the reload value required to wait xExpectedIdleTime
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368 tick periods. -1 is used because this code will execute part way
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369 through one of the tick periods. */
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370 ulReloadValue = portNVIC_SYSTICK_CURRENT_VALUE_REG + ( ulTimerCountsForOneTick * ( xExpectedIdleTime - 1UL ) );
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371 if( ulReloadValue > ulStoppedTimerCompensation )
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373 ulReloadValue -= ulStoppedTimerCompensation;
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376 /* Enter a critical section but don't use the taskENTER_CRITICAL()
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377 method as that will mask interrupts that should exit sleep mode. */
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378 __asm( " cpsid i" );
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383 /* If a context switch is pending or a task is waiting for the scheduler
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384 to be unsuspended then abandon the low power entry. */
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385 if( eTaskConfirmSleepModeStatus() == eAbortSleep )
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387 /* Restart from whatever is left in the count register to complete
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388 this tick period. */
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389 portNVIC_SYSTICK_LOAD_REG = portNVIC_SYSTICK_CURRENT_VALUE_REG;
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391 /* Restart SysTick. */
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392 portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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394 /* Reset the reload register to the value required for normal tick
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396 portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
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398 /* Re-enable interrupts - see comments above __disable_interrupt()
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400 __asm( " cpsie i" );
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404 /* Set the new reload value. */
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405 portNVIC_SYSTICK_LOAD_REG = ulReloadValue;
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407 /* Clear the SysTick count flag and set the count value back to
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409 portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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411 /* Restart SysTick. */
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412 portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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414 /* Sleep until something happens. configPRE_SLEEP_PROCESSING() can
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415 set its parameter to 0 to indicate that its implementation contains
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416 its own wait for interrupt or wait for event instruction, and so wfi
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417 should not be executed again. However, the original expected idle
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418 time variable must remain unmodified, so a copy is taken. */
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419 xModifiableIdleTime = xExpectedIdleTime;
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420 configPRE_SLEEP_PROCESSING( xModifiableIdleTime );
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421 if( xModifiableIdleTime > 0 )
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427 configPOST_SLEEP_PROCESSING( xExpectedIdleTime );
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429 /* Re-enable interrupts to allow the interrupt that brought the MCU
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430 out of sleep mode to execute immediately. see comments above
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431 __disable_interrupt() call above. */
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432 __asm( " cpsie i" );
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436 /* Disable interrupts again because the clock is about to be stopped
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437 and interrupts that execute while the clock is stopped will increase
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438 any slippage between the time maintained by the RTOS and calendar
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440 __asm( " cpsid i" );
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444 /* Disable the SysTick clock without reading the
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445 portNVIC_SYSTICK_CTRL_REG register to ensure the
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446 portNVIC_SYSTICK_COUNT_FLAG_BIT is not cleared if it is set. Again,
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447 the time the SysTick is stopped for is accounted for as best it can
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448 be, but using the tickless mode will inevitably result in some tiny
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449 drift of the time maintained by the kernel with respect to calendar
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451 portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT );
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453 /* Determine if the SysTick clock has already counted to zero and
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454 been set back to the current reload value (the reload back being
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455 correct for the entire expected idle time) or if the SysTick is yet
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456 to count to zero (in which case an interrupt other than the SysTick
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457 must have brought the system out of sleep mode). */
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458 if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
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460 uint32_t ulCalculatedLoadValue;
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462 /* The tick interrupt is already pending, and the SysTick count
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463 reloaded with ulReloadValue. Reset the
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464 portNVIC_SYSTICK_LOAD_REG with whatever remains of this tick
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466 ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );
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468 /* Don't allow a tiny value, or values that have somehow
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469 underflowed because the post sleep hook did something
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470 that took too long. */
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471 if( ( ulCalculatedLoadValue < ulStoppedTimerCompensation ) || ( ulCalculatedLoadValue > ulTimerCountsForOneTick ) )
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473 ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL );
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476 portNVIC_SYSTICK_LOAD_REG = ulCalculatedLoadValue;
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478 /* As the pending tick will be processed as soon as this
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479 function exits, the tick value maintained by the tick is stepped
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480 forward by one less than the time spent waiting. */
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481 ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
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485 /* Something other than the tick interrupt ended the sleep.
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486 Work out how long the sleep lasted rounded to complete tick
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487 periods (not the ulReload value which accounted for part
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489 ulCompletedSysTickDecrements = ( xExpectedIdleTime * ulTimerCountsForOneTick ) - portNVIC_SYSTICK_CURRENT_VALUE_REG;
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491 /* How many complete tick periods passed while the processor
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493 ulCompleteTickPeriods = ulCompletedSysTickDecrements / ulTimerCountsForOneTick;
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495 /* The reload value is set to whatever fraction of a single tick
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497 portNVIC_SYSTICK_LOAD_REG = ( ( ulCompleteTickPeriods + 1UL ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
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500 /* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG
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501 again, then set portNVIC_SYSTICK_LOAD_REG back to its standard
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503 portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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504 portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
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505 vTaskStepTick( ulCompleteTickPeriods );
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506 portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
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508 /* Exit with interrpts enabled. */
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509 __asm( " cpsie i" );
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513 #endif /* configUSE_TICKLESS_IDLE */
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514 /*-----------------------------------------------------------*/
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517 * Setup the systick timer to generate the tick interrupts at the required
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520 #pragma WEAK( vPortSetupTimerInterrupt )
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521 void vPortSetupTimerInterrupt( void )
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523 /* Calculate the constants required to configure the tick interrupt. */
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524 #if( configUSE_TICKLESS_IDLE == 1 )
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526 ulTimerCountsForOneTick = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ );
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527 xMaximumPossibleSuppressedTicks = portMAX_24_BIT_NUMBER / ulTimerCountsForOneTick;
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528 ulStoppedTimerCompensation = portMISSED_COUNTS_FACTOR / ( configCPU_CLOCK_HZ / configSYSTICK_CLOCK_HZ );
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530 #endif /* configUSE_TICKLESS_IDLE */
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532 /* Stop and clear the SysTick. */
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533 portNVIC_SYSTICK_CTRL_REG = 0UL;
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534 portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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536 /* Configure SysTick to interrupt at the requested rate. */
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537 portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
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538 portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT );
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540 /*-----------------------------------------------------------*/
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542 #if( configASSERT_DEFINED == 1 )
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544 void vPortValidateInterruptPriority( void )
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546 extern uint32_t ulPortGetIPSR( void );
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547 uint32_t ulCurrentInterrupt;
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548 uint8_t ucCurrentPriority;
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550 ulCurrentInterrupt = ulPortGetIPSR();
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552 /* Is the interrupt number a user defined interrupt? */
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553 if( ulCurrentInterrupt >= portFIRST_USER_INTERRUPT_NUMBER )
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555 /* Look up the interrupt's priority. */
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556 ucCurrentPriority = pcInterruptPriorityRegisters[ ulCurrentInterrupt ];
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558 /* The following assertion will fail if a service routine (ISR) for
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559 an interrupt that has been assigned a priority above
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560 configMAX_SYSCALL_INTERRUPT_PRIORITY calls an ISR safe FreeRTOS API
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561 function. ISR safe FreeRTOS API functions must *only* be called
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562 from interrupts that have been assigned a priority at or below
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563 configMAX_SYSCALL_INTERRUPT_PRIORITY.
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565 Numerically low interrupt priority numbers represent logically high
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566 interrupt priorities, therefore the priority of the interrupt must
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567 be set to a value equal to or numerically *higher* than
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568 configMAX_SYSCALL_INTERRUPT_PRIORITY.
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570 Interrupts that use the FreeRTOS API must not be left at their
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571 default priority of zero as that is the highest possible priority,
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572 which is guaranteed to be above configMAX_SYSCALL_INTERRUPT_PRIORITY,
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573 and therefore also guaranteed to be invalid.
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575 FreeRTOS maintains separate thread and ISR API functions to ensure
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576 interrupt entry is as fast and simple as possible.
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578 The following links provide detailed information:
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579 http://www.freertos.org/RTOS-Cortex-M3-M4.html
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580 http://www.freertos.org/FAQHelp.html */
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581 configASSERT( ucCurrentPriority >= ucMaxSysCallPriority );
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584 /* Priority grouping: The interrupt controller (NVIC) allows the bits
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585 that define each interrupt's priority to be split between bits that
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586 define the interrupt's pre-emption priority bits and bits that define
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587 the interrupt's sub-priority. For simplicity all bits must be defined
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588 to be pre-emption priority bits. The following assertion will fail if
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589 this is not the case (if some bits represent a sub-priority).
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591 If the application only uses CMSIS libraries for interrupt
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592 configuration then the correct setting can be achieved on all Cortex-M
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593 devices by calling NVIC_SetPriorityGrouping( 0 ); before starting the
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594 scheduler. Note however that some vendor specific peripheral libraries
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595 assume a non-zero priority group setting, in which cases using a value
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596 of zero will result in unpredictable behaviour. */
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597 configASSERT( ( portAIRCR_REG & portPRIORITY_GROUP_MASK ) <= ulMaxPRIGROUPValue );
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600 #endif /* configASSERT_DEFINED */
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