2 FreeRTOS.org V4.2.1 - Copyright (C) 2003-2007 Richard Barry.
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4 This file is part of the FreeRTOS.org distribution.
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6 FreeRTOS.org is free software; you can redistribute it and/or modify
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7 it under the terms of the GNU General Public License as published by
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8 the Free Software Foundation; either version 2 of the License, or
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9 (at your option) any later version.
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11 FreeRTOS.org is distributed in the hope that it will be useful,
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12 but WITHOUT ANY WARRANTY; without even the implied warranty of
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13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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14 GNU General Public License for more details.
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16 You should have received a copy of the GNU General Public License
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17 along with FreeRTOS.org; if not, write to the Free Software
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18 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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20 A special exception to the GPL can be applied should you wish to distribute
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21 a combined work that includes FreeRTOS.org, without being obliged to provide
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22 the source code for any proprietary components. See the licensing section
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23 of http://www.FreeRTOS.org for full details of how and when the exception
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26 ***************************************************************************
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27 See http://www.FreeRTOS.org for documentation, latest information, license
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28 and contact details. Please ensure to read the configuration and relevant
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29 port sections of the online documentation.
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31 Also see http://www.SafeRTOS.com for an IEC 61508 compliant version along
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32 with commercial development and support options.
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33 ***************************************************************************
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40 + AVR port - Replaced the inb() and outb() functions with direct memory
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41 access. This allows the port to be built with the 20050414 build of
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46 #include <avr/interrupt.h>
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48 #include "FreeRTOS.h"
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51 /*-----------------------------------------------------------
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52 * Implementation of functions defined in portable.h for the AVR port.
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53 *----------------------------------------------------------*/
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55 /* Start tasks with interrupts enables. */
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56 #define portFLAGS_INT_ENABLED ( ( portSTACK_TYPE ) 0x80 )
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58 /* Hardware constants for timer 1. */
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59 #define portCLEAR_COUNTER_ON_MATCH ( ( unsigned portCHAR ) 0x08 )
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60 #define portPRESCALE_64 ( ( unsigned portCHAR ) 0x03 )
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61 #define portCLOCK_PRESCALER ( ( unsigned portLONG ) 64 )
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62 #define portCOMPARE_MATCH_A_INTERRUPT_ENABLE ( ( unsigned portCHAR ) 0x10 )
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64 /*-----------------------------------------------------------*/
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66 /* We require the address of the pxCurrentTCB variable, but don't want to know
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67 any details of its type. */
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68 typedef void tskTCB;
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69 extern volatile tskTCB * volatile pxCurrentTCB;
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71 /*-----------------------------------------------------------*/
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74 * Macro to save all the general purpose registers, the save the stack pointer
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77 * The first thing we do is save the flags then disable interrupts. This is to
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78 * guard our stack against having a context switch interrupt after we have already
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79 * pushed the registers onto the stack - causing the 32 registers to be on the
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82 * r1 is set to zero as the compiler expects it to be thus, however some
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83 * of the math routines make use of R1.
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85 * The interrupts will have been disabled during the call to portSAVE_CONTEXT()
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86 * so we need not worry about reading/writing to the stack pointer.
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89 #define portSAVE_CONTEXT() \
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90 asm volatile ( "push r0 \n\t" \
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91 "in r0, __SREG__ \n\t" \
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126 "lds r26, pxCurrentTCB \n\t" \
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127 "lds r27, pxCurrentTCB + 1 \n\t" \
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128 "in r0, 0x3d \n\t" \
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130 "in r0, 0x3e \n\t" \
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135 * Opposite to portSAVE_CONTEXT(). Interrupts will have been disabled during
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136 * the context save so we can write to the stack pointer.
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139 #define portRESTORE_CONTEXT() \
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140 asm volatile ( "lds r26, pxCurrentTCB \n\t" \
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141 "lds r27, pxCurrentTCB + 1 \n\t" \
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142 "ld r28, x+ \n\t" \
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143 "out __SP_L__, r28 \n\t" \
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144 "ld r29, x+ \n\t" \
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145 "out __SP_H__, r29 \n\t" \
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178 "out __SREG__, r0 \n\t" \
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182 /*-----------------------------------------------------------*/
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185 * Perform hardware setup to enable ticks from timer 1, compare match A.
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187 static void prvSetupTimerInterrupt( void );
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188 /*-----------------------------------------------------------*/
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191 * See header file for description.
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193 portSTACK_TYPE *pxPortInitialiseStack( portSTACK_TYPE *pxTopOfStack, pdTASK_CODE pxCode, void *pvParameters )
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195 unsigned portSHORT usAddress;
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197 /* Place a few bytes of known values on the bottom of the stack.
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198 This is just useful for debugging. */
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200 *pxTopOfStack = 0x11;
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202 *pxTopOfStack = 0x22;
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204 *pxTopOfStack = 0x33;
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207 /* Simulate how the stack would look after a call to vPortYield() generated by
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210 /*lint -e950 -e611 -e923 Lint doesn't like this much - but nothing I can do about it. */
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212 /* The start of the task code will be popped off the stack last, so place
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214 usAddress = ( unsigned portSHORT ) pxCode;
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215 *pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned portSHORT ) 0x00ff );
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219 *pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned portSHORT ) 0x00ff );
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222 /* Next simulate the stack as if after a call to portSAVE_CONTEXT().
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223 portSAVE_CONTEXT places the flags on the stack immediately after r0
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224 to ensure the interrupts get disabled as soon as possible, and so ensuring
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225 the stack use is minimal should a context switch interrupt occur. */
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226 *pxTopOfStack = ( portSTACK_TYPE ) 0x00; /* R0 */
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228 *pxTopOfStack = portFLAGS_INT_ENABLED;
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232 /* Now the remaining registers. The compiler expects R1 to be 0. */
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233 *pxTopOfStack = ( portSTACK_TYPE ) 0x00; /* R1 */
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235 *pxTopOfStack = ( portSTACK_TYPE ) 0x02; /* R2 */
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237 *pxTopOfStack = ( portSTACK_TYPE ) 0x03; /* R3 */
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239 *pxTopOfStack = ( portSTACK_TYPE ) 0x04; /* R4 */
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241 *pxTopOfStack = ( portSTACK_TYPE ) 0x05; /* R5 */
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243 *pxTopOfStack = ( portSTACK_TYPE ) 0x06; /* R6 */
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245 *pxTopOfStack = ( portSTACK_TYPE ) 0x07; /* R7 */
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247 *pxTopOfStack = ( portSTACK_TYPE ) 0x08; /* R8 */
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249 *pxTopOfStack = ( portSTACK_TYPE ) 0x09; /* R9 */
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251 *pxTopOfStack = ( portSTACK_TYPE ) 0x10; /* R10 */
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253 *pxTopOfStack = ( portSTACK_TYPE ) 0x11; /* R11 */
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255 *pxTopOfStack = ( portSTACK_TYPE ) 0x12; /* R12 */
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257 *pxTopOfStack = ( portSTACK_TYPE ) 0x13; /* R13 */
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259 *pxTopOfStack = ( portSTACK_TYPE ) 0x14; /* R14 */
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261 *pxTopOfStack = ( portSTACK_TYPE ) 0x15; /* R15 */
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263 *pxTopOfStack = ( portSTACK_TYPE ) 0x16; /* R16 */
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265 *pxTopOfStack = ( portSTACK_TYPE ) 0x17; /* R17 */
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267 *pxTopOfStack = ( portSTACK_TYPE ) 0x18; /* R18 */
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269 *pxTopOfStack = ( portSTACK_TYPE ) 0x19; /* R19 */
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271 *pxTopOfStack = ( portSTACK_TYPE ) 0x20; /* R20 */
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273 *pxTopOfStack = ( portSTACK_TYPE ) 0x21; /* R21 */
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275 *pxTopOfStack = ( portSTACK_TYPE ) 0x22; /* R22 */
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277 *pxTopOfStack = ( portSTACK_TYPE ) 0x23; /* R23 */
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280 /* Place the parameter on the stack in the expected location. */
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281 usAddress = ( unsigned portSHORT ) pvParameters;
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282 *pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned portSHORT ) 0x00ff );
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286 *pxTopOfStack = ( portSTACK_TYPE ) ( usAddress & ( unsigned portSHORT ) 0x00ff );
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289 *pxTopOfStack = ( portSTACK_TYPE ) 0x26; /* R26 X */
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291 *pxTopOfStack = ( portSTACK_TYPE ) 0x27; /* R27 */
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293 *pxTopOfStack = ( portSTACK_TYPE ) 0x28; /* R28 Y */
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295 *pxTopOfStack = ( portSTACK_TYPE ) 0x29; /* R29 */
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297 *pxTopOfStack = ( portSTACK_TYPE ) 0x30; /* R30 Z */
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299 *pxTopOfStack = ( portSTACK_TYPE ) 0x031; /* R31 */
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302 /*lint +e950 +e611 +e923 */
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304 return pxTopOfStack;
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306 /*-----------------------------------------------------------*/
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308 portBASE_TYPE xPortStartScheduler( void )
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310 /* In this port we ignore the parameter and use the configUSE_PREEMPTION
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311 definition instead. */
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313 /* Setup the hardware to generate the tick. */
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314 prvSetupTimerInterrupt();
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316 /* Restore the context of the first task that is going to run. */
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317 portRESTORE_CONTEXT();
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319 /* Simulate a function call end as generated by the compiler. We will now
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320 jump to the start of the task the context of which we have just restored. */
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321 asm volatile ( "ret" );
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323 /* Should not get here. */
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326 /*-----------------------------------------------------------*/
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328 void vPortEndScheduler( void )
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330 /* It is unlikely that the AVR port will get stopped. If required simply
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331 disable the tick interrupt here. */
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333 /*-----------------------------------------------------------*/
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336 * Manual context switch. The first thing we do is save the registers so we
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337 * can use a naked attribute.
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339 void vPortYield( void ) __attribute__ ( ( naked ) );
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340 void vPortYield( void )
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342 portSAVE_CONTEXT();
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343 vTaskSwitchContext();
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344 portRESTORE_CONTEXT();
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346 asm volatile ( "ret" );
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348 /*-----------------------------------------------------------*/
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351 * Context switch function used by the tick. This must be identical to
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352 * vPortYield() from the call to vTaskSwitchContext() onwards. The only
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353 * difference from vPortYield() is the tick count is incremented as the
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354 * call comes from the tick ISR.
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356 void vPortYieldFromTick( void ) __attribute__ ( ( naked ) );
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357 void vPortYieldFromTick( void )
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359 portSAVE_CONTEXT();
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360 vTaskIncrementTick();
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361 vTaskSwitchContext();
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362 portRESTORE_CONTEXT();
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364 asm volatile ( "ret" );
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366 /*-----------------------------------------------------------*/
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369 * Setup timer 1 compare match A to generate a tick interrupt.
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371 static void prvSetupTimerInterrupt( void )
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373 unsigned portLONG ulCompareMatch;
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374 unsigned portCHAR ucHighByte, ucLowByte;
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376 /* Using 16bit timer 1 to generate the tick. Correct fuses must be
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377 selected for the configCPU_CLOCK_HZ clock. */
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379 ulCompareMatch = configCPU_CLOCK_HZ / configTICK_RATE_HZ;
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381 /* We only have 16 bits so have to scale to get our required tick rate. */
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382 ulCompareMatch /= portCLOCK_PRESCALER;
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384 /* Adjust for correct value. */
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385 ulCompareMatch -= ( unsigned portLONG ) 1;
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387 /* Setup compare match value for compare match A. Interrupts are disabled
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388 before this is called so we need not worry here. */
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389 ucLowByte = ( unsigned portCHAR ) ( ulCompareMatch & ( unsigned portLONG ) 0xff );
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390 ulCompareMatch >>= 8;
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391 ucHighByte = ( unsigned portCHAR ) ( ulCompareMatch & ( unsigned portLONG ) 0xff );
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392 OCR1AH = ucHighByte;
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393 OCR1AL = ucLowByte;
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395 /* Setup clock source and compare match behaviour. */
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396 ucLowByte = portCLEAR_COUNTER_ON_MATCH | portPRESCALE_64;
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397 TCCR1B = ucLowByte;
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399 /* Enable the interrupt - this is okay as interrupt are currently globally
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402 ucLowByte |= portCOMPARE_MATCH_A_INTERRUPT_ENABLE;
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405 /*-----------------------------------------------------------*/
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407 #if configUSE_PREEMPTION == 1
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410 * Tick ISR for preemptive scheduler. We can use a naked attribute as
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411 * the context is saved at the start of vPortYieldFromTick(). The tick
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412 * count is incremented after the context is saved.
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414 void SIG_OUTPUT_COMPARE1A( void ) __attribute__ ( ( signal, naked ) );
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415 void SIG_OUTPUT_COMPARE1A( void )
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417 vPortYieldFromTick();
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418 asm volatile ( "reti" );
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423 * Tick ISR for the cooperative scheduler. All this does is increment the
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424 * tick count. We don't need to switch context, this can only be done by
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425 * manual calls to taskYIELD();
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427 void SIG_OUTPUT_COMPARE1A( void ) __attribute__ ( ( signal ) );
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428 void SIG_OUTPUT_COMPARE1A( void )
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430 vTaskIncrementTick();
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