2 FreeRTOS V7.5.2 - Copyright (C) 2013 Real Time Engineers Ltd.
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4 VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.
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6 ***************************************************************************
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8 * FreeRTOS provides completely free yet professionally developed, *
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9 * robust, strictly quality controlled, supported, and cross *
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10 * platform software that has become a de facto standard. *
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12 * Help yourself get started quickly and support the FreeRTOS *
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13 * project by purchasing a FreeRTOS tutorial book, reference *
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14 * manual, or both from: http://www.FreeRTOS.org/Documentation *
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18 ***************************************************************************
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20 This file is part of the FreeRTOS distribution.
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22 FreeRTOS is free software; you can redistribute it and/or modify it under
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23 the terms of the GNU General Public License (version 2) as published by the
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24 Free Software Foundation >>!AND MODIFIED BY!<< the FreeRTOS exception.
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26 >>! NOTE: The modification to the GPL is included to allow you to distribute
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27 >>! a combined work that includes FreeRTOS without being obliged to provide
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28 >>! the source code for proprietary components outside of the FreeRTOS
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31 FreeRTOS is distributed in the hope that it will be useful, but WITHOUT ANY
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32 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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33 FOR A PARTICULAR PURPOSE. Full license text is available from the following
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34 link: http://www.freertos.org/a00114.html
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38 ***************************************************************************
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40 * Having a problem? Start by reading the FAQ "My application does *
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41 * not run, what could be wrong?" *
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43 * http://www.FreeRTOS.org/FAQHelp.html *
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45 ***************************************************************************
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47 http://www.FreeRTOS.org - Documentation, books, training, latest versions,
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48 license and Real Time Engineers Ltd. contact details.
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50 http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products,
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51 including FreeRTOS+Trace - an indispensable productivity tool, a DOS
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52 compatible FAT file system, and our tiny thread aware UDP/IP stack.
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54 http://www.OpenRTOS.com - Real Time Engineers ltd license FreeRTOS to High
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55 Integrity Systems to sell under the OpenRTOS brand. Low cost OpenRTOS
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56 licenses offer ticketed support, indemnification and middleware.
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58 http://www.SafeRTOS.com - High Integrity Systems also provide a safety
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59 engineered and independently SIL3 certified version for use in safety and
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60 mission critical applications that require provable dependability.
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65 /* Standard includes. */
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68 /* FreeRTOS includes. */
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69 #include "FreeRTOS.h"
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72 /* Library includes. */
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77 * When configCREATE_LOW_POWER_DEMO is set to 1 then the tick interrupt
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78 * is generated by the AST. The AST configuration and handling functions are
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79 * defined in this file.
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81 * When configCREATE_LOW_POWER_DEMO is set to 0 the tick interrupt is
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82 * generated by the standard FreeRTOS Cortex-M port layer, which uses the
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85 #if configCREATE_LOW_POWER_DEMO == 1
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87 /* Constants required to pend a PendSV interrupt from the tick ISR if the
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88 preemptive scheduler is being used. These are just standard bits and registers
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89 within the Cortex-M core itself. */
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90 #define portNVIC_INT_CTRL_REG ( * ( ( volatile unsigned long * ) 0xe000ed04 ) )
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91 #define portNVIC_PENDSVSET_BIT ( 1UL << 28UL )
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93 /* The alarm used to generate interrupts in the asynchronous timer. */
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94 #define portAST_ALARM_CHANNEL 0
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96 /*-----------------------------------------------------------*/
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99 * The tick interrupt is generated by the asynchronous timer. The default tick
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100 * interrupt handler cannot be used (even with the AST being handled from the
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101 * tick hook function) because the default tick interrupt accesses the SysTick
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102 * registers when configUSE_TICKLESS_IDLE set to 1. AST_ALARM_Handler() is the
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103 * default name for the AST alarm interrupt. This definition overrides the
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104 * default implementation that is weakly defined in the interrupt vector table
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107 void AST_ALARM_Handler(void);
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110 * Functions that disable and enable the AST respectively, not returning until
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111 * the operation is known to have taken effect.
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113 static void prvDisableAST( void );
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114 static void prvEnableAST( void );
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116 /*-----------------------------------------------------------*/
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118 /* Calculate how many clock increments make up a single tick period. */
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119 static const uint32_t ulAlarmValueForOneTick = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ );
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121 /* Holds the maximum number of ticks that can be suppressed - which is
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122 basically how far into the future an interrupt can be generated. Set
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123 during initialisation. */
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124 static portTickType xMaximumPossibleSuppressedTicks = 0;
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126 /* Flag set from the tick interrupt to allow the sleep processing to know if
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127 sleep mode was exited because of an AST interrupt or a different interrupt. */
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128 static volatile uint32_t ulTickFlag = pdFALSE;
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130 /* The AST counter is stopped temporarily each time it is re-programmed. The
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131 following variable offsets the AST counter alarm value by the number of AST
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132 counts that would typically be missed while the counter was stopped to compensate
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133 for the lost time. _RB_ Value needs calculating correctly. */
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134 static uint32_t ulStoppedTimerCompensation = 2 / ( configCPU_CLOCK_HZ / configSYSTICK_CLOCK_HZ );
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136 /*-----------------------------------------------------------*/
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138 /* The tick interrupt handler. This is always the same other than the part that
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139 clears the interrupt, which is specific to the clock being used to generate the
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141 void AST_ALARM_Handler(void)
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143 /* Protect incrementing the tick with an interrupt safe critical section. */
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144 ( void ) portSET_INTERRUPT_MASK_FROM_ISR();
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146 if( xTaskIncrementTick() != pdFALSE )
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148 portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;
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151 /* Just completely clear the interrupt mask on exit by passing 0 because
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152 it is known that this interrupt will only ever execute with the lowest
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153 possible interrupt priority. */
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155 portCLEAR_INTERRUPT_MASK_FROM_ISR( 0 );
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157 /* The CPU woke because of a tick. */
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158 ulTickFlag = pdTRUE;
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160 /* If this is the first tick since exiting tickless mode then the AST needs
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161 to be reconfigured to generate interrupts at the defined tick frequency. */
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162 ast_write_alarm0_value( AST, ulAlarmValueForOneTick );
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164 /* Ensure the interrupt is clear before exiting. */
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165 ast_clear_interrupt_flag( AST, AST_INTERRUPT_ALARM );
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167 /*-----------------------------------------------------------*/
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169 /* Override the default definition of vPortSetupTimerInterrupt() that is weakly
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170 defined in the FreeRTOS Cortex-M3 port layer with a version that configures the
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171 asynchronous timer (AST) to generate the tick interrupt. */
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172 void vPortSetupTimerInterrupt( void )
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174 struct ast_config ast_conf;
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176 /* Ensure the AST can bring the CPU out of sleep mode. */
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177 sleepmgr_lock_mode( SLEEPMGR_RET );
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179 /* Ensure the 32KHz oscillator is enabled. */
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180 if( osc_is_ready( OSC_ID_OSC32 ) == pdFALSE )
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182 osc_enable( OSC_ID_OSC32 );
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183 osc_wait_ready( OSC_ID_OSC32 );
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186 /* Enable the AST itself. */
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189 ast_conf.mode = AST_COUNTER_MODE; /* Simple up counter. */
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190 ast_conf.osc_type = AST_OSC_32KHZ;
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191 ast_conf.psel = 0; /* No prescale so the actual frequency is 32KHz/2. */
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192 ast_conf.counter = 0;
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193 ast_set_config( AST, &ast_conf );
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195 /* The AST alarm interrupt is used as the tick interrupt. Ensure the alarm
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196 status starts clear. */
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197 ast_clear_interrupt_flag( AST, AST_INTERRUPT_ALARM );
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199 /* Enable wakeup from alarm 0 in the AST and power manager. */
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200 ast_enable_wakeup( AST, AST_WAKEUP_ALARM );
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201 bpm_enable_wakeup_source( BPM, ( 1 << BPM_BKUPWEN_AST ) );
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203 /* Tick interrupt MUST execute at the lowest interrupt priority. */
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204 NVIC_SetPriority( AST_ALARM_IRQn, configLIBRARY_LOWEST_INTERRUPT_PRIORITY);
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205 ast_enable_interrupt( AST, AST_INTERRUPT_ALARM );
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206 NVIC_ClearPendingIRQ( AST_ALARM_IRQn );
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207 NVIC_EnableIRQ( AST_ALARM_IRQn );
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209 /* Automatically clear the counter on interrupt. */
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210 ast_enable_counter_clear_on_alarm( AST, portAST_ALARM_CHANNEL );
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212 /* Start with the tick active and generating a tick with regular period. */
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213 ast_write_alarm0_value( AST, ulAlarmValueForOneTick );
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214 ast_write_counter_value( AST, 0 );
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216 /* See the comments where xMaximumPossibleSuppressedTicks is declared. */
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217 xMaximumPossibleSuppressedTicks = ULONG_MAX / ulAlarmValueForOneTick;
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219 /*-----------------------------------------------------------*/
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221 static void prvDisableAST( void )
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223 while( ast_is_busy( AST ) )
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225 /* Nothing to do here, just waiting. */
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227 AST->AST_CR &= ~( AST_CR_EN );
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228 while( ast_is_busy( AST ) )
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230 /* Nothing to do here, just waiting. */
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233 /*-----------------------------------------------------------*/
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235 static void prvEnableAST( void )
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237 while( ast_is_busy( AST ) )
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239 /* Nothing to do here, just waiting. */
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241 AST->AST_CR |= AST_CR_EN;
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242 while( ast_is_busy( AST ) )
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244 /* Nothing to do here, just waiting. */
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247 /*-----------------------------------------------------------*/
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249 /* Override the default definition of vPortSuppressTicksAndSleep() that is weakly
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250 defined in the FreeRTOS Cortex-M3 port layet with a version that manages the
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251 asynchronous timer (AST), as the tick is generated from the low power AST and
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252 not the SysTick as would normally be the case on a Cortex-M. */
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253 void vPortSuppressTicksAndSleep( portTickType xExpectedIdleTime )
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255 uint32_t ulAlarmValue, ulCompleteTickPeriods;
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256 eSleepModeStatus eSleepAction;
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257 portTickType xModifiableIdleTime;
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258 enum sleepmgr_mode xSleepMode;
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260 /* THIS FUNCTION IS CALLED WITH THE SCHEDULER SUSPENDED. */
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262 /* Make sure the AST reload value does not overflow the counter. */
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263 if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
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265 xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
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268 /* Calculate the reload value required to wait xExpectedIdleTime tick
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270 ulAlarmValue = ulAlarmValueForOneTick * xExpectedIdleTime;
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271 if( ulAlarmValue > ulStoppedTimerCompensation )
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273 /* Compensate for the fact that the AST is going to be stopped
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275 ulAlarmValue -= ulStoppedTimerCompensation;
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278 /* Stop the AST momentarily. The time the AST is stopped for is accounted
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279 for as best it can be, but using the tickless mode will inevitably result in
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280 some tiny drift of the time maintained by the kernel with respect to
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284 /* Enter a critical section but don't use the taskENTER_CRITICAL() method as
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285 that will mask interrupts that should exit sleep mode. */
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286 __asm volatile( "cpsid i \n\t"
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289 /* The tick flag is set to false before sleeping. If it is true when sleep
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290 mode is exited then sleep mode was probably exited because the tick was
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291 suppressed for the entire xExpectedIdleTime period. */
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292 ulTickFlag = pdFALSE;
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294 /* If a context switch is pending then abandon the low power entry as
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295 the context switch might have been pended by an external interrupt that
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296 requires processing. */
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297 eSleepAction = eTaskConfirmSleepModeStatus();
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298 if( eSleepAction == eAbortSleep )
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300 /* Restart tick. */
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303 /* Re-enable interrupts - see comments above the cpsid instruction()
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305 __asm volatile( "cpsie i" );
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309 /* Adjust the alarm value to take into account that the current time
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310 slice is already partially complete. */
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311 ulAlarmValue -= ast_read_counter_value( AST );
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312 ast_write_alarm0_value( AST, ulAlarmValue );
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314 /* Restart the AST. */
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317 /* Allow the application to define some pre-sleep processing. */
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318 xModifiableIdleTime = xExpectedIdleTime;
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319 configPRE_SLEEP_PROCESSING( xModifiableIdleTime );
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321 /* xExpectedIdleTime being set to 0 by configPRE_SLEEP_PROCESSING()
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322 means the application defined code has already executed the WAIT
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324 if( xModifiableIdleTime > 0 )
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326 /* Find the deepest allowable sleep mode. */
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327 xSleepMode = sleepmgr_get_sleep_mode();
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329 if( xSleepMode != SLEEPMGR_ACTIVE )
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331 /* Sleep until something happens. */
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332 bpm_sleep( BPM, xSleepMode );
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336 /* Allow the application to define some post sleep processing. */
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337 configPOST_SLEEP_PROCESSING( xModifiableIdleTime );
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339 /* Stop AST. Again, the time the SysTick is stopped for is accounted
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340 for as best it can be, but using the tickless mode will inevitably
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341 result in some tiny drift of the time maintained by the kernel with
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342 respect to calendar time. */
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345 /* Re-enable interrupts - see comments above the cpsid instruction()
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347 __asm volatile( "cpsie i" );
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349 if( ulTickFlag != pdFALSE )
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351 /* The tick interrupt has already executed, although because this
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352 function is called with the scheduler suspended the actual tick
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353 processing will not occur until after this function has exited.
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354 Reset the alarm value with whatever remains of this tick period. */
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355 ulAlarmValue = ulAlarmValueForOneTick - ast_read_counter_value( AST );
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356 ast_write_alarm0_value( AST, ulAlarmValue );
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358 /* The tick interrupt handler will already have pended the tick
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359 processing in the kernel. As the pending tick will be processed as
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360 soon as this function exits, the tick value maintained by the tick
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361 is stepped forward by one less than the time spent sleeping. The
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362 actual stepping of the tick appears later in this function. */
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363 ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
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367 /* Something other than the tick interrupt ended the sleep. How
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368 many complete tick periods passed while the processor was
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370 ulCompleteTickPeriods = ast_read_counter_value( AST ) / ulAlarmValueForOneTick;
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372 /* The alarm value is set to whatever fraction of a single tick
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374 ulAlarmValue = ast_read_counter_value( AST ) - ( ulCompleteTickPeriods * ulAlarmValueForOneTick );
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375 ast_write_alarm0_value( AST, ulAlarmValue );
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378 /* Restart the AST so it runs up to the alarm value. The alarm value
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379 will get set to the value required to generate exactly one tick period
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380 the next time the AST interrupt executes. */
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383 /* Wind the tick forward by the number of tick periods that the CPU
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384 remained in a low power state. */
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385 vTaskStepTick( ulCompleteTickPeriods );
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390 #endif /* configCREATE_LOW_POWER_DEMO == 1 */
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