2 FreeRTOS V7.5.0 - 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 /*-----------------------------------------------------------
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66 * Implementation of functions defined in portable.h for the ARM CM4F port.
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67 *----------------------------------------------------------*/
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69 /* Scheduler includes. */
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70 #include "FreeRTOS.h"
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74 #error This port can only be used when the project options are configured to enable hardware floating point support.
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77 #ifndef configSYSTICK_CLOCK_HZ
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78 #define configSYSTICK_CLOCK_HZ configCPU_CLOCK_HZ
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81 /* Constants required to manipulate the core. Registers first... */
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82 #define portNVIC_SYSTICK_CTRL_REG ( * ( ( volatile unsigned long * ) 0xe000e010 ) )
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83 #define portNVIC_SYSTICK_LOAD_REG ( * ( ( volatile unsigned long * ) 0xe000e014 ) )
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84 #define portNVIC_SYSTICK_CURRENT_VALUE_REG ( * ( ( volatile unsigned long * ) 0xe000e018 ) )
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85 #define portNVIC_SYSPRI2_REG ( * ( ( volatile unsigned long * ) 0xe000ed20 ) )
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86 /* ...then bits in the registers. */
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87 #define portNVIC_SYSTICK_CLK_BIT ( 1UL << 2UL )
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88 #define portNVIC_SYSTICK_INT_BIT ( 1UL << 1UL )
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89 #define portNVIC_SYSTICK_ENABLE_BIT ( 1UL << 0UL )
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90 #define portNVIC_SYSTICK_COUNT_FLAG_BIT ( 1UL << 16UL )
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91 #define portNVIC_PENDSVCLEAR_BIT ( 1UL << 27UL )
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92 #define portNVIC_PEND_SYSTICK_CLEAR_BIT ( 1UL << 25UL )
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94 #define portNVIC_PENDSV_PRI ( ( ( unsigned long ) configKERNEL_INTERRUPT_PRIORITY ) << 16UL )
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95 #define portNVIC_SYSTICK_PRI ( ( ( unsigned long ) configKERNEL_INTERRUPT_PRIORITY ) << 24UL )
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97 /* Constants required to check the validity of an interrupt prority. */
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98 #define portFIRST_USER_INTERRUPT_NUMBER ( 16 )
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99 #define portNVIC_IP_REGISTERS_OFFSET_16 ( 0xE000E3F0 )
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100 #define portAIRCR_REG ( * ( ( volatile unsigned long * ) 0xE000ED0C ) )
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101 #define portPRIORITY_GROUP_MASK ( 0x07UL << 8UL )
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103 /* Constants required to manipulate the VFP. */
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104 #define portFPCCR ( ( volatile unsigned long * ) 0xe000ef34 ) /* Floating point context control register. */
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105 #define portASPEN_AND_LSPEN_BITS ( 0x3UL << 30UL )
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107 /* Constants required to set up the initial stack. */
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108 #define portINITIAL_XPSR ( 0x01000000 )
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109 #define portINITIAL_EXEC_RETURN ( 0xfffffffd )
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111 /* The systick is a 24-bit counter. */
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112 #define portMAX_24_BIT_NUMBER ( 0xffffffUL )
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114 /* A fiddle factor to estimate the number of SysTick counts that would have
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115 occurred while the SysTick counter is stopped during tickless idle
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117 #define portMISSED_COUNTS_FACTOR ( 45UL )
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119 /* Each task maintains its own interrupt status in the critical nesting
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121 static unsigned portBASE_TYPE uxCriticalNesting = 0xaaaaaaaa;
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124 * Setup the timer to generate the tick interrupts. The implementation in this
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125 * file is weak to allow application writers to change the timer used to
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126 * generate the tick interrupt.
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128 void vPortSetupTimerInterrupt( void );
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131 * Exception handlers.
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133 void xPortPendSVHandler( void ) __attribute__ (( naked ));
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134 void xPortSysTickHandler( void );
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135 void vPortSVCHandler( void ) __attribute__ (( naked ));
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138 * Start first task is a separate function so it can be tested in isolation.
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140 static void prvPortStartFirstTask( void ) __attribute__ (( naked ));
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143 * Function to enable the VFP.
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145 static void vPortEnableVFP( void ) __attribute__ (( naked ));
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147 /*-----------------------------------------------------------*/
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150 * The number of SysTick increments that make up one tick period.
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152 #if configUSE_TICKLESS_IDLE == 1
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153 static unsigned long ulTimerCountsForOneTick = 0;
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154 #endif /* configUSE_TICKLESS_IDLE */
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157 * The maximum number of tick periods that can be suppressed is limited by the
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158 * 24 bit resolution of the SysTick timer.
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160 #if configUSE_TICKLESS_IDLE == 1
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161 static unsigned long xMaximumPossibleSuppressedTicks = 0;
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162 #endif /* configUSE_TICKLESS_IDLE */
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165 * Compensate for the CPU cycles that pass while the SysTick is stopped (low
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166 * power functionality only.
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168 #if configUSE_TICKLESS_IDLE == 1
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169 static unsigned long ulStoppedTimerCompensation = 0;
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170 #endif /* configUSE_TICKLESS_IDLE */
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173 * Used by the portASSERT_IF_INTERRUPT_PRIORITY_INVALID() macro to ensure
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174 * FreeRTOS API functions are not called from interrupts that have been assigned
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175 * a priority above configMAX_SYSCALL_INTERRUPT_PRIORITY.
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177 #if ( configASSERT_DEFINED == 1 )
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178 static unsigned char ucMaxSysCallPriority = 0;
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179 static const volatile unsigned char * const pcInterruptPriorityRegisters = ( const volatile unsigned char * const ) portNVIC_IP_REGISTERS_OFFSET_16;
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180 #endif /* configASSERT_DEFINED */
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182 /*-----------------------------------------------------------*/
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185 * See header file for description.
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187 portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
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189 /* Simulate the stack frame as it would be created by a context switch
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192 /* Offset added to account for the way the MCU uses the stack on entry/exit
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193 of interrupts, and to ensure alignment. */
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196 *pxTopOfStack = portINITIAL_XPSR; /* xPSR */
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198 *pxTopOfStack = ( portSTACK_TYPE ) pxCode; /* PC */
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200 *pxTopOfStack = 0; /* LR */
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202 /* Save code space by skipping register initialisation. */
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203 pxTopOfStack -= 5; /* R12, R3, R2 and R1. */
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204 *pxTopOfStack = ( portSTACK_TYPE ) pvParameters; /* R0 */
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206 /* A save method is being used that requires each task to maintain its
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207 own exec return value. */
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209 *pxTopOfStack = portINITIAL_EXEC_RETURN;
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211 pxTopOfStack -= 8; /* R11, R10, R9, R8, R7, R6, R5 and R4. */
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213 return pxTopOfStack;
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215 /*-----------------------------------------------------------*/
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217 void vPortSVCHandler( void )
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220 " ldr r3, pxCurrentTCBConst2 \n" /* Restore the context. */
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221 " ldr r1, [r3] \n" /* Use pxCurrentTCBConst to get the pxCurrentTCB address. */
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222 " ldr r0, [r1] \n" /* The first item in pxCurrentTCB is the task top of stack. */
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223 " ldmia r0!, {r4-r11, r14} \n" /* Pop the registers that are not automatically saved on exception entry and the critical nesting count. */
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224 " msr psp, r0 \n" /* Restore the task stack pointer. */
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226 " msr basepri, r0 \n"
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230 "pxCurrentTCBConst2: .word pxCurrentTCB \n"
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233 /*-----------------------------------------------------------*/
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235 static void prvPortStartFirstTask( void )
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238 " ldr r0, =0xE000ED08 \n" /* Use the NVIC offset register to locate the stack. */
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241 " msr msp, r0 \n" /* Set the msp back to the start of the stack. */
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242 " cpsie i \n" /* Globally enable interrupts. */
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243 " svc 0 \n" /* System call to start first task. */
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247 /*-----------------------------------------------------------*/
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250 * See header file for description.
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252 portBASE_TYPE xPortStartScheduler( void )
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254 /* configMAX_SYSCALL_INTERRUPT_PRIORITY must not be set to 0.
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255 See http://www.FreeRTOS.org/RTOS-Cortex-M3-M4.html */
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256 configASSERT( configMAX_SYSCALL_INTERRUPT_PRIORITY );
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258 #if( configASSERT_DEFINED == 1 )
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260 volatile unsigned long ulOriginalPriority;
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261 volatile char * const pcFirstUserPriorityRegister = ( volatile char * const ) ( portNVIC_IP_REGISTERS_OFFSET_16 + portFIRST_USER_INTERRUPT_NUMBER );
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263 /* Determine the maximum priority from which ISR safe FreeRTOS API
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264 functions can be called. ISR safe functions are those that end in
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265 "FromISR". FreeRTOS maintains separate thread and ISR API functions to
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266 ensure interrupt entry is as fast and simple as possible.
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268 Save the interrupt priority value that is about to be clobbered. */
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269 ulOriginalPriority = *pcFirstUserPriorityRegister;
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271 /* Write the configMAX_SYSCALL_INTERRUPT_PRIORITY value to an interrupt
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272 priority register. */
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273 *pcFirstUserPriorityRegister = configMAX_SYSCALL_INTERRUPT_PRIORITY;
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275 /* Read back the written priority to obtain its value as seen by the
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276 hardware, which will only implement a subset of the priority bits. */
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277 ucMaxSysCallPriority = *pcFirstUserPriorityRegister;
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279 /* Restore the clobbered interrupt priority register to its original
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281 *pcFirstUserPriorityRegister = ulOriginalPriority;
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283 #endif /* conifgASSERT_DEFINED */
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285 /* Make PendSV and SysTick the lowest priority interrupts. */
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286 portNVIC_SYSPRI2_REG |= portNVIC_PENDSV_PRI;
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287 portNVIC_SYSPRI2_REG |= portNVIC_SYSTICK_PRI;
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289 /* Start the timer that generates the tick ISR. Interrupts are disabled
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291 vPortSetupTimerInterrupt();
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293 /* Initialise the critical nesting count ready for the first task. */
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294 uxCriticalNesting = 0;
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296 /* Ensure the VFP is enabled - it should be anyway. */
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299 /* Lazy save always. */
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300 *( portFPCCR ) |= portASPEN_AND_LSPEN_BITS;
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302 /* Start the first task. */
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303 prvPortStartFirstTask();
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305 /* Should not get here! */
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308 /*-----------------------------------------------------------*/
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310 void vPortEndScheduler( void )
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312 /* It is unlikely that the CM4F port will require this function as there
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313 is nothing to return to. */
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315 /*-----------------------------------------------------------*/
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317 void vPortYield( void )
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319 /* Set a PendSV to request a context switch. */
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320 portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;
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322 /* Barriers are normally not required but do ensure the code is completely
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323 within the specified behaviour for the architecture. */
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324 __asm volatile( "dsb" );
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325 __asm volatile( "isb" );
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327 /*-----------------------------------------------------------*/
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329 void vPortEnterCritical( void )
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331 portDISABLE_INTERRUPTS();
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332 uxCriticalNesting++;
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333 __asm volatile( "dsb" );
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334 __asm volatile( "isb" );
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336 /*-----------------------------------------------------------*/
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338 void vPortExitCritical( void )
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340 uxCriticalNesting--;
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341 if( uxCriticalNesting == 0 )
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343 portENABLE_INTERRUPTS();
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346 /*-----------------------------------------------------------*/
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348 __attribute__(( naked )) unsigned long ulPortSetInterruptMask( void )
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352 " mrs r0, basepri \n" \
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354 " msr basepri, r1 \n" \
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356 :: "i" ( configMAX_SYSCALL_INTERRUPT_PRIORITY ) : "r0", "r1" \
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359 /* This return will not be reached but is necessary to prevent compiler
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363 /*-----------------------------------------------------------*/
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365 __attribute__(( naked )) void vPortClearInterruptMask( unsigned long ulNewMaskValue )
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369 " msr basepri, r0 \n" \
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374 /* Just to avoid compiler warnings. */
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375 ( void ) ulNewMaskValue;
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377 /*-----------------------------------------------------------*/
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379 void xPortPendSVHandler( void )
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381 /* This is a naked function. */
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387 " ldr r3, pxCurrentTCBConst \n" /* Get the location of the current TCB. */
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390 " tst r14, #0x10 \n" /* Is the task using the FPU context? If so, push high vfp registers. */
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392 " vstmdbeq r0!, {s16-s31} \n"
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394 " stmdb r0!, {r4-r11, r14} \n" /* Save the core registers. */
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396 " str r0, [r2] \n" /* Save the new top of stack into the first member of the TCB. */
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398 " stmdb sp!, {r3, r14} \n"
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400 " msr basepri, r0 \n"
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401 " bl vTaskSwitchContext \n"
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403 " msr basepri, r0 \n"
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404 " ldmia sp!, {r3, r14} \n"
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406 " ldr r1, [r3] \n" /* The first item in pxCurrentTCB is the task top of stack. */
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409 " ldmia r0!, {r4-r11, r14} \n" /* Pop the core registers. */
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411 " tst r14, #0x10 \n" /* Is the task using the FPU context? If so, pop the high vfp registers too. */
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413 " vldmiaeq r0!, {s16-s31} \n"
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419 "pxCurrentTCBConst: .word pxCurrentTCB \n"
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420 ::"i"(configMAX_SYSCALL_INTERRUPT_PRIORITY)
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423 /*-----------------------------------------------------------*/
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425 void xPortSysTickHandler( void )
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427 /* The SysTick runs at the lowest interrupt priority, so when this interrupt
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428 executes all interrupts must be unmasked. There is therefore no need to
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429 save and then restore the interrupt mask value as its value is already
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431 ( void ) portSET_INTERRUPT_MASK_FROM_ISR();
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433 /* Increment the RTOS tick. */
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434 if( xTaskIncrementTick() != pdFALSE )
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436 /* A context switch is required. Context switching is performed in
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437 the PendSV interrupt. Pend the PendSV interrupt. */
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438 portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;
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441 portCLEAR_INTERRUPT_MASK_FROM_ISR( 0 );
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443 /*-----------------------------------------------------------*/
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445 #if configUSE_TICKLESS_IDLE == 1
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447 __attribute__((weak)) void vPortSuppressTicksAndSleep( portTickType xExpectedIdleTime )
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449 unsigned long ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements;
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450 portTickType xModifiableIdleTime;
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452 /* Make sure the SysTick reload value does not overflow the counter. */
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453 if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
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455 xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
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458 /* Stop the SysTick momentarily. The time the SysTick is stopped for
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459 is accounted for as best it can be, but using the tickless mode will
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460 inevitably result in some tiny drift of the time maintained by the
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461 kernel with respect to calendar time. */
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462 portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT;
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464 /* Calculate the reload value required to wait xExpectedIdleTime
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465 tick periods. -1 is used because this code will execute part way
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466 through one of the tick periods. */
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467 ulReloadValue = portNVIC_SYSTICK_CURRENT_VALUE_REG + ( ulTimerCountsForOneTick * ( xExpectedIdleTime - 1UL ) );
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468 if( ulReloadValue > ulStoppedTimerCompensation )
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470 ulReloadValue -= ulStoppedTimerCompensation;
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473 /* Enter a critical section but don't use the taskENTER_CRITICAL()
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474 method as that will mask interrupts that should exit sleep mode. */
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475 __asm volatile( "cpsid i" );
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477 /* If a context switch is pending or a task is waiting for the scheduler
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478 to be unsuspended then abandon the low power entry. */
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479 if( eTaskConfirmSleepModeStatus() == eAbortSleep )
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481 /* Restart SysTick. */
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482 portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;
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484 /* Re-enable interrupts - see comments above the cpsid instruction()
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486 __asm volatile( "cpsie i" );
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490 /* Set the new reload value. */
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491 portNVIC_SYSTICK_LOAD_REG = ulReloadValue;
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493 /* Clear the SysTick count flag and set the count value back to
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495 portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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497 /* Restart SysTick. */
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498 portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;
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500 /* Sleep until something happens. configPRE_SLEEP_PROCESSING() can
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501 set its parameter to 0 to indicate that its implementation contains
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502 its own wait for interrupt or wait for event instruction, and so wfi
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503 should not be executed again. However, the original expected idle
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504 time variable must remain unmodified, so a copy is taken. */
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505 xModifiableIdleTime = xExpectedIdleTime;
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506 configPRE_SLEEP_PROCESSING( xModifiableIdleTime );
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507 if( xModifiableIdleTime > 0 )
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509 __asm volatile( "dsb" );
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510 __asm volatile( "wfi" );
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511 __asm volatile( "isb" );
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513 configPOST_SLEEP_PROCESSING( xExpectedIdleTime );
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515 /* Stop SysTick. Again, the time the SysTick is stopped for is
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516 accounted for as best it can be, but using the tickless mode will
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517 inevitably result in some tiny drift of the time maintained by the
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518 kernel with respect to calendar time. */
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519 portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT;
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521 /* Re-enable interrupts - see comments above the cpsid instruction()
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523 __asm volatile( "cpsie i" );
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525 if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
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527 /* The tick interrupt has already executed, and the SysTick
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528 count reloaded with ulReloadValue. Reset the
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529 portNVIC_SYSTICK_LOAD_REG with whatever remains of this tick
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531 portNVIC_SYSTICK_LOAD_REG = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );
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533 /* The tick interrupt handler will already have pended the tick
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534 processing in the kernel. As the pending tick will be
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535 processed as soon as this function exits, the tick value
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536 maintained by the tick is stepped forward by one less than the
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537 time spent waiting. */
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538 ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
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542 /* Something other than the tick interrupt ended the sleep.
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543 Work out how long the sleep lasted rounded to complete tick
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544 periods (not the ulReload value which accounted for part
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546 ulCompletedSysTickDecrements = ( xExpectedIdleTime * ulTimerCountsForOneTick ) - portNVIC_SYSTICK_CURRENT_VALUE_REG;
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548 /* How many complete tick periods passed while the processor
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550 ulCompleteTickPeriods = ulCompletedSysTickDecrements / ulTimerCountsForOneTick;
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552 /* The reload value is set to whatever fraction of a single tick
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554 portNVIC_SYSTICK_LOAD_REG = ( ( ulCompleteTickPeriods + 1 ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
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557 /* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD_REG
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558 again, then set portNVIC_SYSTICK_LOAD_REG back to its standard
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560 portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
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561 portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;
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563 vTaskStepTick( ulCompleteTickPeriods );
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565 /* The counter must start by the time the reload value is reset. */
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566 configASSERT( portNVIC_SYSTICK_CURRENT_VALUE_REG );
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567 portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;
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571 #endif /* #if configUSE_TICKLESS_IDLE */
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572 /*-----------------------------------------------------------*/
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575 * Setup the systick timer to generate the tick interrupts at the required
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578 __attribute__(( weak )) void vPortSetupTimerInterrupt( void )
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580 /* Calculate the constants required to configure the tick interrupt. */
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581 #if configUSE_TICKLESS_IDLE == 1
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583 ulTimerCountsForOneTick = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ );
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584 xMaximumPossibleSuppressedTicks = portMAX_24_BIT_NUMBER / ulTimerCountsForOneTick;
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585 ulStoppedTimerCompensation = portMISSED_COUNTS_FACTOR / ( configCPU_CLOCK_HZ / configSYSTICK_CLOCK_HZ );
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587 #endif /* configUSE_TICKLESS_IDLE */
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589 /* Configure SysTick to interrupt at the requested rate. */
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590 portNVIC_SYSTICK_LOAD_REG = ( configSYSTICK_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;;
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591 portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;
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593 /*-----------------------------------------------------------*/
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595 /* This is a naked function. */
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596 static void vPortEnableVFP( void )
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600 " ldr.w r0, =0xE000ED88 \n" /* The FPU enable bits are in the CPACR. */
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603 " orr r1, r1, #( 0xf << 20 ) \n" /* Enable CP10 and CP11 coprocessors, then save back. */
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608 /*-----------------------------------------------------------*/
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610 #if( configASSERT_DEFINED == 1 )
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612 void vPortValidateInterruptPriority( void )
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614 unsigned long ulCurrentInterrupt;
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615 unsigned char ucCurrentPriority;
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617 /* Obtain the number of the currently executing interrupt. */
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618 __asm volatile( "mrs %0, ipsr" : "=r"( ulCurrentInterrupt ) );
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620 /* Is the interrupt number a user defined interrupt? */
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621 if( ulCurrentInterrupt >= portFIRST_USER_INTERRUPT_NUMBER )
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623 /* Look up the interrupt's priority. */
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624 ucCurrentPriority = pcInterruptPriorityRegisters[ ulCurrentInterrupt ];
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626 /* The following assertion will fail if a service routine (ISR) for
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627 an interrupt that has been assigned a priority above
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628 configMAX_SYSCALL_INTERRUPT_PRIORITY calls an ISR safe FreeRTOS API
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629 function. ISR safe FreeRTOS API functions must *only* be called
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630 from interrupts that have been assigned a priority at or below
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631 configMAX_SYSCALL_INTERRUPT_PRIORITY.
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633 Numerically low interrupt priority numbers represent logically high
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634 interrupt priorities, therefore the priority of the interrupt must
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635 be set to a value equal to or numerically *higher* than
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636 configMAX_SYSCALL_INTERRUPT_PRIORITY.
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638 Interrupts that use the FreeRTOS API must not be left at their
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639 default priority of zero as that is the highest possible priority,
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640 which is guaranteed to be above configMAX_SYSCALL_INTERRUPT_PRIORITY,
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641 and therefore also guaranteed to be invalid.
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643 FreeRTOS maintains separate thread and ISR API functions to ensure
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644 interrupt entry is as fast and simple as possible.
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646 The following links provide detailed information:
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647 http://www.freertos.org/RTOS-Cortex-M3-M4.html
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648 http://www.freertos.org/FAQHelp.html */
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649 configASSERT( ucCurrentPriority >= ucMaxSysCallPriority );
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652 /* Priority grouping: The interrupt controller (NVIC) allows the bits
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653 that define each interrupt's priority to be split between bits that
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654 define the interrupt's pre-emption priority bits and bits that define
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655 the interrupt's sub-priority. For simplicity all bits must be defined
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656 to be pre-emption priority bits. The following assertion will fail if
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657 this is not the case (if some bits represent a sub-priority).
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659 If CMSIS libraries are being used then the correct setting can be
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660 achieved by calling NVIC_SetPriorityGrouping( 0 ); before starting the
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662 configASSERT( ( portAIRCR_REG & portPRIORITY_GROUP_MASK ) == 0 );
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665 #endif /* configASSERT_DEFINED */
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