2 FreeRTOS V7.6.0 - Copyright (C) 2013 Real Time Engineers Ltd.
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5 VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.
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7 ***************************************************************************
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9 * FreeRTOS provides completely free yet professionally developed, *
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10 * robust, strictly quality controlled, supported, and cross *
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11 * platform software that has become a de facto standard. *
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13 * Help yourself get started quickly and support the FreeRTOS *
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14 * project by purchasing a FreeRTOS tutorial book, reference *
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15 * manual, or both from: http://www.FreeRTOS.org/Documentation *
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19 ***************************************************************************
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21 This file is part of the FreeRTOS distribution.
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23 FreeRTOS is free software; you can redistribute it and/or modify it under
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24 the terms of the GNU General Public License (version 2) as published by the
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25 Free Software Foundation >>!AND MODIFIED BY!<< the FreeRTOS exception.
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27 >>! NOTE: The modification to the GPL is included to allow you to distribute
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28 >>! a combined work that includes FreeRTOS without being obliged to provide
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29 >>! the source code for proprietary components outside of the FreeRTOS
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32 FreeRTOS is distributed in the hope that it will be useful, but WITHOUT ANY
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33 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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34 FOR A PARTICULAR PURPOSE. Full license text is available from the following
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35 link: http://www.freertos.org/a00114.html
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39 ***************************************************************************
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41 * Having a problem? Start by reading the FAQ "My application does *
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42 * not run, what could be wrong?" *
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44 * http://www.FreeRTOS.org/FAQHelp.html *
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46 ***************************************************************************
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48 http://www.FreeRTOS.org - Documentation, books, training, latest versions,
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49 license and Real Time Engineers Ltd. contact details.
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51 http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products,
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52 including FreeRTOS+Trace - an indispensable productivity tool, a DOS
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53 compatible FAT file system, and our tiny thread aware UDP/IP stack.
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55 http://www.OpenRTOS.com - Real Time Engineers ltd license FreeRTOS to High
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56 Integrity Systems to sell under the OpenRTOS brand. Low cost OpenRTOS
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57 licenses offer ticketed support, indemnification and middleware.
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59 http://www.SafeRTOS.com - High Integrity Systems also provide a safety
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60 engineered and independently SIL3 certified version for use in safety and
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61 mission critical applications that require provable dependability.
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66 /*-----------------------------------------------------------
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67 * Implementation of functions defined in portable.h for the ARM CM0 port.
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68 *----------------------------------------------------------*/
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70 /* Scheduler includes. */
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71 #include "FreeRTOS.h"
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74 /* Constants required to manipulate the NVIC. */
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75 #define portNVIC_SYSTICK_CTRL ( ( volatile unsigned long *) 0xe000e010 )
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76 #define portNVIC_SYSTICK_LOAD ( ( volatile unsigned long *) 0xe000e014 )
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77 #define portNVIC_INT_CTRL ( ( volatile unsigned long *) 0xe000ed04 )
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78 #define portNVIC_SYSPRI2 ( ( volatile unsigned long *) 0xe000ed20 )
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79 #define portNVIC_SYSTICK_CLK 0x00000004
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80 #define portNVIC_SYSTICK_INT 0x00000002
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81 #define portNVIC_SYSTICK_ENABLE 0x00000001
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82 #define portNVIC_PENDSVSET 0x10000000
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83 #define portMIN_INTERRUPT_PRIORITY ( 255UL )
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84 #define portNVIC_PENDSV_PRI ( portMIN_INTERRUPT_PRIORITY << 16UL )
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85 #define portNVIC_SYSTICK_PRI ( portMIN_INTERRUPT_PRIORITY << 24UL )
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87 /* Constants required to set up the initial stack. */
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88 #define portINITIAL_XPSR ( 0x01000000 )
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90 /* Let the user override the pre-loading of the initial LR with the address of
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91 prvTaskExitError() in case is messes up unwinding of the stack in the
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93 #ifdef configTASK_RETURN_ADDRESS
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94 #define portTASK_RETURN_ADDRESS configTASK_RETURN_ADDRESS
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96 #define portTASK_RETURN_ADDRESS prvTaskExitError
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99 /* Each task maintains its own interrupt status in the critical nesting
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101 static unsigned portBASE_TYPE uxCriticalNesting = 0xaaaaaaaa;
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104 * Setup the timer to generate the tick interrupts.
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106 static void prvSetupTimerInterrupt( void );
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109 * Exception handlers.
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111 void xPortPendSVHandler( void ) __attribute__ (( naked ));
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112 void xPortSysTickHandler( void );
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113 void vPortSVCHandler( void );
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116 * Start first task is a separate function so it can be tested in isolation.
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118 static void vPortStartFirstTask( void ) __attribute__ (( naked ));
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121 * Used to catch tasks that attempt to return from their implementing function.
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123 static void prvTaskExitError( void );
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125 /*-----------------------------------------------------------*/
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128 * See header file for description.
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130 portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
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132 /* Simulate the stack frame as it would be created by a context switch
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134 pxTopOfStack--; /* Offset added to account for the way the MCU uses the stack on entry/exit of interrupts. */
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135 *pxTopOfStack = portINITIAL_XPSR; /* xPSR */
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137 *pxTopOfStack = ( portSTACK_TYPE ) pxCode; /* PC */
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139 *pxTopOfStack = ( portSTACK_TYPE ) portTASK_RETURN_ADDRESS; /* LR */
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140 pxTopOfStack -= 5; /* R12, R3, R2 and R1. */
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141 *pxTopOfStack = ( portSTACK_TYPE ) pvParameters; /* R0 */
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142 pxTopOfStack -= 8; /* R11..R4. */
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144 return pxTopOfStack;
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146 /*-----------------------------------------------------------*/
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148 static void prvTaskExitError( void )
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150 /* A function that implements a task must not exit or attempt to return to
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151 its caller as there is nothing to return to. If a task wants to exit it
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152 should instead call vTaskDelete( NULL ).
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154 Artificially force an assert() to be triggered if configASSERT() is
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155 defined, then stop here so application writers can catch the error. */
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156 configASSERT( uxCriticalNesting == ~0UL );
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157 portDISABLE_INTERRUPTS();
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160 /*-----------------------------------------------------------*/
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162 void vPortSVCHandler( void )
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164 /* This function is no longer used, but retained for backward
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167 /*-----------------------------------------------------------*/
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169 void vPortStartFirstTask( void )
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171 /* The MSP stack is not reset as, unlike on M3/4 parts, there is no vector
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172 table offset register that can be used to locate the initial stack value.
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173 Not all M0 parts have the application vector table at address 0. */
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175 " ldr r2, pxCurrentTCBConst2 \n" /* Obtain location of pxCurrentTCB. */
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177 " ldr r0, [r3] \n" /* The first item in pxCurrentTCB is the task top of stack. */
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178 " add r0, #32 \n" /* Discard everything up to r0. */
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179 " msr psp, r0 \n" /* This is now the new top of stack to use in the task. */
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180 " movs r0, #2 \n" /* Switch to the psp stack. */
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181 " msr CONTROL, r0 \n"
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182 " pop {r0-r5} \n" /* Pop the registers that are saved automatically. */
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183 " mov lr, r5 \n" /* lr is now in r5. */
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184 " cpsie i \n" /* The first task has its context and interrupts can be enabled. */
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185 " pop {pc} \n" /* Finally, pop the PC to jump to the user defined task code. */
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188 "pxCurrentTCBConst2: .word pxCurrentTCB "
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191 /*-----------------------------------------------------------*/
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194 * See header file for description.
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196 portBASE_TYPE xPortStartScheduler( void )
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198 /* Make PendSV, CallSV and SysTick the same priroity as the kernel. */
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199 *(portNVIC_SYSPRI2) |= portNVIC_PENDSV_PRI;
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200 *(portNVIC_SYSPRI2) |= portNVIC_SYSTICK_PRI;
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202 /* Start the timer that generates the tick ISR. Interrupts are disabled
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204 prvSetupTimerInterrupt();
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206 /* Initialise the critical nesting count ready for the first task. */
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207 uxCriticalNesting = 0;
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209 /* Start the first task. */
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210 vPortStartFirstTask();
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212 /* Should never get here as the tasks will now be executing! Call the task
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213 exit error function to prevent compiler warnings about a static function
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214 not being called in the case that the application writer overrides this
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215 functionality by defining configTASK_RETURN_ADDRESS. */
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216 prvTaskExitError();
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218 /* Should not get here! */
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221 /*-----------------------------------------------------------*/
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223 void vPortEndScheduler( void )
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225 /* Not implemented in ports where there is nothing to return to.
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226 Artificially force an assert. */
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227 configASSERT( uxCriticalNesting == 1000UL );
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229 /*-----------------------------------------------------------*/
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231 void vPortYield( void )
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233 /* Set a PendSV to request a context switch. */
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234 *( portNVIC_INT_CTRL ) = portNVIC_PENDSVSET;
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236 /* Barriers are normally not required but do ensure the code is completely
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237 within the specified behaviour for the architecture. */
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238 __asm volatile( "dsb" );
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239 __asm volatile( "isb" );
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241 /*-----------------------------------------------------------*/
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243 void vPortEnterCritical( void )
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245 portDISABLE_INTERRUPTS();
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246 uxCriticalNesting++;
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247 __asm volatile( "dsb" );
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248 __asm volatile( "isb" );
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250 /*-----------------------------------------------------------*/
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252 void vPortExitCritical( void )
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254 configASSERT( uxCriticalNesting );
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255 uxCriticalNesting--;
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256 if( uxCriticalNesting == 0 )
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258 portENABLE_INTERRUPTS();
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261 /*-----------------------------------------------------------*/
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263 unsigned long ulSetInterruptMaskFromISR( void )
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266 " mrs r0, PRIMASK \n"
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271 /* To avoid compiler warnings. This line will never be reached. */
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274 /*-----------------------------------------------------------*/
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276 void vClearInterruptMaskFromISR( unsigned long ulMask )
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279 " msr PRIMASK, r0 \n"
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283 /* Just to avoid compiler warning. */
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286 /*-----------------------------------------------------------*/
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288 void xPortPendSVHandler( void )
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290 /* This is a naked function. */
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296 " ldr r3, pxCurrentTCBConst \n" /* Get the location of the current TCB. */
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299 " sub r0, r0, #32 \n" /* Make space for the remaining low registers. */
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300 " str r0, [r2] \n" /* Save the new top of stack. */
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301 " stmia r0!, {r4-r7} \n" /* Store the low registers that are not saved automatically. */
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302 " mov r4, r8 \n" /* Store the high registers. */
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306 " stmia r0!, {r4-r7} \n"
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308 " push {r3, r14} \n"
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310 " bl vTaskSwitchContext \n"
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312 " pop {r2, r3} \n" /* lr goes in r3. r2 now holds tcb pointer. */
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315 " ldr r0, [r1] \n" /* The first item in pxCurrentTCB is the task top of stack. */
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316 " add r0, r0, #16 \n" /* Move to the high registers. */
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317 " ldmia r0!, {r4-r7} \n" /* Pop the high registers. */
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323 " msr psp, r0 \n" /* Remember the new top of stack for the task. */
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325 " sub r0, r0, #32 \n" /* Go back for the low registers that are not automatically restored. */
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326 " ldmia r0!, {r4-r7} \n" /* Pop low registers. */
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331 "pxCurrentTCBConst: .word pxCurrentTCB "
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334 /*-----------------------------------------------------------*/
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336 void xPortSysTickHandler( void )
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338 unsigned long ulPreviousMask;
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340 ulPreviousMask = portSET_INTERRUPT_MASK_FROM_ISR();
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342 /* Increment the RTOS tick. */
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343 if( xTaskIncrementTick() != pdFALSE )
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345 /* Pend a context switch. */
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346 *(portNVIC_INT_CTRL) = portNVIC_PENDSVSET;
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349 portCLEAR_INTERRUPT_MASK_FROM_ISR( ulPreviousMask );
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351 /*-----------------------------------------------------------*/
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354 * Setup the systick timer to generate the tick interrupts at the required
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357 void prvSetupTimerInterrupt( void )
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359 /* Configure SysTick to interrupt at the requested rate. */
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360 *(portNVIC_SYSTICK_LOAD) = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
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361 *(portNVIC_SYSTICK_CTRL) = portNVIC_SYSTICK_CLK | portNVIC_SYSTICK_INT | portNVIC_SYSTICK_ENABLE;
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363 /*-----------------------------------------------------------*/
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