begriffs open source - cmsis-freertos/blob - Source/portable/ThirdParty/GCC/ATmega/port.c

   1 /*
   2  * FreeRTOS Kernel V11.2.0
   3  * Copyright (C) 2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
   4  *
   5  * SPDX-License-Identifier: MIT
   6  *
   7  * Permission is hereby granted, free of charge, to any person obtaining a copy of
   8  * this software and associated documentation files (the "Software"), to deal in
   9  * the Software without restriction, including without limitation the rights to
  10  * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
  11  * the Software, and to permit persons to whom the Software is furnished to do so,
  12  * subject to the following conditions:
  13  *
  14  * The above copyright notice and this permission notice shall be included in all
  15  * copies or substantial portions of the Software.
  16  *
  17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  18  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
  19  * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
  20  * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
  21  * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  22  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  23  *
  24  * https://www.FreeRTOS.org
  25  * https://github.com/FreeRTOS
  26  *
  27  */
  28
  29
  30 #include <stdlib.h>
  31
  32 #include <avr/io.h>
  33 #include <avr/interrupt.h>
  34 #include <avr/wdt.h>
  35
  36 #include "FreeRTOS.h"
  37 #include "task.h"
  38
  39 /*-----------------------------------------------------------
  40 * Implementation of functions defined in portable.h for the AVR port.
  41 *----------------------------------------------------------*/
  42
  43 /* Start tasks with interrupts enabled. */
  44 #define portFLAGS_INT_ENABLED    ( ( StackType_t ) 0x80 )
  45
  46 #if defined( portUSE_WDTO )
  47     #warning "Watchdog Timer used for scheduler."
  48     #define portSCHEDULER_ISR    WDT_vect
  49
  50 #elif defined( portUSE_TIMER0 )
  51 /* Hardware constants for Timer0. */
  52     #warning "Timer0 used for scheduler."
  53     #define portSCHEDULER_ISR                       TIMER0_COMPA_vect
  54     #define portCLEAR_COUNTER_ON_MATCH              ( ( uint8_t ) _BV( WGM01 ) )
  55     #define portPRESCALE_1024                       ( ( uint8_t ) ( _BV( CS02 ) | _BV( CS00 ) ) )
  56     #define portCLOCK_PRESCALER                     ( ( uint32_t ) 1024 )
  57     #define portCOMPARE_MATCH_A_INTERRUPT_ENABLE    ( ( uint8_t ) _BV( OCIE0A ) )
  58     #define portOCRL                                OCR0A
  59     #define portTCCRa                               TCCR0A
  60     #define portTCCRb                               TCCR0B
  61     #define portTIMSK                               TIMSK0
  62     #define portTIFR                                TIFR0
  63
  64 #else /* if defined( portUSE_WDTO ) */
  65     #error "No Timer defined for scheduler"
  66 #endif /* if defined( portUSE_WDTO ) */
  67
  68 /*-----------------------------------------------------------*/
  69
  70 /* We require the address of the pxCurrentTCB variable, but don't want to know
  71  * any details of its type. */
  72 typedef void TCB_t;
  73 extern volatile TCB_t * volatile pxCurrentTCB;
  74
  75 /*-----------------------------------------------------------*/
  76
  77 /**
  78  *  Enable the watchdog timer, configuring it for expire after
  79  *  (value) timeout (which is a combination of the WDP0
  80  *  through WDP3 bits).
  81  *
  82  *  This function is derived from <avr/wdt.h> but enables only
  83  *  the interrupt bit (WDIE), rather than the reset bit (WDE).
  84  *
  85  *  Can't find it documented but the WDT, once enabled,
  86  *  rolls over and fires a new interrupt each time.
  87  *
  88  *  See also the symbolic constants WDTO_15MS et al.
  89  *
  90  *  Updated to match avr-libc 2.0.0
  91  */
  92
  93 #if defined( portUSE_WDTO )
  94
  95     static __inline__
  96     __attribute__( ( __always_inline__ ) )
  97     void wdt_interrupt_enable( const uint8_t value )
  98     {
  99         if( _SFR_IO_REG_P( _WD_CONTROL_REG ) )
 100         {
 101             __asm__ __volatile__ (
 102                 "in __tmp_reg__,__SREG__"   "\n\t"
 103                 "cli"                       "\n\t"
 104                 "wdr"                       "\n\t"
 105                 "out %0, %1"                "\n\t"
 106                 "out __SREG__,__tmp_reg__"  "\n\t"
 107                 "out %0, %2"                "\n\t"
 108                 : /* no outputs */
 109                 : "I" ( _SFR_IO_ADDR( _WD_CONTROL_REG ) ),
 110                 "r" ( ( uint8_t ) ( _BV( _WD_CHANGE_BIT ) | _BV( WDE ) ) ),
 111                 "r" ( ( uint8_t ) ( ( value & 0x08 ? _WD_PS3_MASK : 0x00 ) |
 112                                     _BV( WDIF ) | _BV( WDIE ) | ( value & 0x07 ) ) )
 113                 : "r0"
 114                 );
 115         }
 116         else
 117         {
 118             __asm__ __volatile__ (
 119                 "in __tmp_reg__,__SREG__"   "\n\t"
 120                 "cli"                       "\n\t"
 121                 "wdr"                       "\n\t"
 122                 "sts %0, %1"                "\n\t"
 123                 "out __SREG__,__tmp_reg__"  "\n\t"
 124                 "sts %0, %2"                "\n\t"
 125                 : /* no outputs */
 126                 : "n" ( _SFR_MEM_ADDR( _WD_CONTROL_REG ) ),
 127                 "r" ( ( uint8_t ) ( _BV( _WD_CHANGE_BIT ) | _BV( WDE ) ) ),
 128                 "r" ( ( uint8_t ) ( ( value & 0x08 ? _WD_PS3_MASK : 0x00 ) |
 129                                     _BV( WDIF ) | _BV( WDIE ) | ( value & 0x07 ) ) )
 130                 : "r0"
 131                 );
 132         }
 133     }
 134 #endif /* if defined( portUSE_WDTO ) */
 135
 136 /*-----------------------------------------------------------*/
 137
 138 /**
 139  *  Enable the watchdog timer, configuring it for expire after
 140  *  (value) timeout (which is a combination of the WDP0
 141  *  through WDP3 bits).
 142  *
 143  *  This function is derived from <avr/wdt.h> but enables both
 144  *  the reset bit (WDE), and the interrupt bit (WDIE).
 145  *
 146  *  This will ensure that if the interrupt is not serviced
 147  *  before the second timeout, the AVR will reset.
 148  *
 149  *  Servicing the interrupt automatically clears it,
 150  *  and ensures the AVR does not reset.
 151  *
 152  *  Can't find it documented but the WDT, once enabled,
 153  *  rolls over and fires a new interrupt each time.
 154  *
 155  *  See also the symbolic constants WDTO_15MS et al.
 156  *
 157  *  Updated to match avr-libc 2.0.0
 158  */
 159
 160 #if defined( portUSE_WDTO )
 161
 162     static __inline__
 163     __attribute__( ( __always_inline__ ) )
 164     void wdt_interrupt_reset_enable( const uint8_t value )
 165     {
 166         if( _SFR_IO_REG_P( _WD_CONTROL_REG ) )
 167         {
 168             __asm__ __volatile__ (
 169                 "in __tmp_reg__,__SREG__"   "\n\t"
 170                 "cli"                       "\n\t"
 171                 "wdr"                       "\n\t"
 172                 "out %0, %1"                "\n\t"
 173                 "out __SREG__,__tmp_reg__"  "\n\t"
 174                 "out %0, %2"                "\n\t"
 175                 : /* no outputs */
 176                 : "I" ( _SFR_IO_ADDR( _WD_CONTROL_REG ) ),
 177                 "r" ( ( uint8_t ) ( _BV( _WD_CHANGE_BIT ) | _BV( WDE ) ) ),
 178                 "r" ( ( uint8_t ) ( ( value & 0x08 ? _WD_PS3_MASK : 0x00 ) |
 179                                     _BV( WDIF ) | _BV( WDIE ) | _BV( WDE ) | ( value & 0x07 ) ) )
 180                 : "r0"
 181                 );
 182         }
 183         else
 184         {
 185             __asm__ __volatile__ (
 186                 "in __tmp_reg__,__SREG__"   "\n\t"
 187                 "cli"                       "\n\t"
 188                 "wdr"                       "\n\t"
 189                 "sts %0, %1"                "\n\t"
 190                 "out __SREG__,__tmp_reg__"  "\n\t"
 191                 "sts %0, %2"                "\n\t"
 192                 : /* no outputs */
 193                 : "n" ( _SFR_MEM_ADDR( _WD_CONTROL_REG ) ),
 194                 "r" ( ( uint8_t ) ( _BV( _WD_CHANGE_BIT ) | _BV( WDE ) ) ),
 195                 "r" ( ( uint8_t ) ( ( value & 0x08 ? _WD_PS3_MASK : 0x00 ) |
 196                                     _BV( WDIF ) | _BV( WDIE ) | _BV( WDE ) | ( value & 0x07 ) ) )
 197                 : "r0"
 198                 );
 199         }
 200     }
 201 #endif /* if defined( portUSE_WDTO ) */
 202
 203 /*-----------------------------------------------------------*/
 204
 205 /*
 206  * Macro to save all the general purpose registers, the save the stack pointer
 207  * into the TCB.
 208  *
 209  * The first thing we do is save the flags then disable interrupts. This is to
 210  * guard our stack against having a context switch interrupt after we have already
 211  * pushed the registers onto the stack - causing the 32 registers to be on the
 212  * stack twice.
 213  *
 214  * r1 is set to zero (__zero_reg__) as the compiler expects it to be thus, however
 215  * some of the math routines make use of R1.
 216  *
 217  * r0 is set to __tmp_reg__ as the compiler expects it to be thus.
 218  *
 219  * #if defined(__AVR_HAVE_RAMPZ__)
 220  * #define __RAMPZ__ 0x3B
 221  * #endif
 222  *
 223  * #if defined(__AVR_3_BYTE_PC__)
 224  * #define __EIND__ 0x3C
 225  * #endif
 226  *
 227  * The interrupts will have been disabled during the call to portSAVE_CONTEXT()
 228  * so we need not worry about reading/writing to the stack pointer.
 229  */
 230 #if defined( __AVR_3_BYTE_PC__ ) && defined( __AVR_HAVE_RAMPZ__ )
 231 /* 3-Byte PC Save  with RAMPZ */
 232     #define portSAVE_CONTEXT()                                                   \
 233     __asm__ __volatile__ ( "push   __tmp_reg__                             \n\t" \
 234                            "in     __tmp_reg__, __SREG__                   \n\t" \
 235                            "cli                                            \n\t" \
 236                            "push   __tmp_reg__                             \n\t" \
 237                            "in     __tmp_reg__, 0x3B                       \n\t" \
 238                            "push   __tmp_reg__                             \n\t" \
 239                            "in     __tmp_reg__, 0x3C                       \n\t" \
 240                            "push   __tmp_reg__                             \n\t" \
 241                            "push   __zero_reg__                            \n\t" \
 242                            "clr    __zero_reg__                            \n\t" \
 243                            "push   r2                                      \n\t" \
 244                            "push   r3                                      \n\t" \
 245                            "push   r4                                      \n\t" \
 246                            "push   r5                                      \n\t" \
 247                            "push   r6                                      \n\t" \
 248                            "push   r7                                      \n\t" \
 249                            "push   r8                                      \n\t" \
 250                            "push   r9                                      \n\t" \
 251                            "push   r10                                     \n\t" \
 252                            "push   r11                                     \n\t" \
 253                            "push   r12                                     \n\t" \
 254                            "push   r13                                     \n\t" \
 255                            "push   r14                                     \n\t" \
 256                            "push   r15                                     \n\t" \
 257                            "push   r16                                     \n\t" \
 258                            "push   r17                                     \n\t" \
 259                            "push   r18                                     \n\t" \
 260                            "push   r19                                     \n\t" \
 261                            "push   r20                                     \n\t" \
 262                            "push   r21                                     \n\t" \
 263                            "push   r22                                     \n\t" \
 264                            "push   r23                                     \n\t" \
 265                            "push   r24                                     \n\t" \
 266                            "push   r25                                     \n\t" \
 267                            "push   r26                                     \n\t" \
 268                            "push   r27                                     \n\t" \
 269                            "push   r28                                     \n\t" \
 270                            "push   r29                                     \n\t" \
 271                            "push   r30                                     \n\t" \
 272                            "push   r31                                     \n\t" \
 273                            "lds    r26, pxCurrentTCB                       \n\t" \
 274                            "lds    r27, pxCurrentTCB + 1                   \n\t" \
 275                            "in     __tmp_reg__, __SP_L__                   \n\t" \
 276                            "st     x+, __tmp_reg__                         \n\t" \
 277                            "in     __tmp_reg__, __SP_H__                   \n\t" \
 278                            "st     x+, __tmp_reg__                         \n\t" \
 279                            );
 280 #elif defined( __AVR_HAVE_RAMPZ__ )
 281 /* 2-Byte PC Save  with RAMPZ */
 282     #define portSAVE_CONTEXT()                                                   \
 283     __asm__ __volatile__ ( "push   __tmp_reg__                             \n\t" \
 284                            "in     __tmp_reg__, __SREG__                   \n\t" \
 285                            "cli                                            \n\t" \
 286                            "push   __tmp_reg__                             \n\t" \
 287                            "in     __tmp_reg__, 0x3B                       \n\t" \
 288                            "push   __tmp_reg__                             \n\t" \
 289                            "push   __zero_reg__                            \n\t" \
 290                            "clr    __zero_reg__                            \n\t" \
 291                            "push   r2                                      \n\t" \
 292                            "push   r3                                      \n\t" \
 293                            "push   r4                                      \n\t" \
 294                            "push   r5                                      \n\t" \
 295                            "push   r6                                      \n\t" \
 296                            "push   r7                                      \n\t" \
 297                            "push   r8                                      \n\t" \
 298                            "push   r9                                      \n\t" \
 299                            "push   r10                                     \n\t" \
 300                            "push   r11                                     \n\t" \
 301                            "push   r12                                     \n\t" \
 302                            "push   r13                                     \n\t" \
 303                            "push   r14                                     \n\t" \
 304                            "push   r15                                     \n\t" \
 305                            "push   r16                                     \n\t" \
 306                            "push   r17                                     \n\t" \
 307                            "push   r18                                     \n\t" \
 308                            "push   r19                                     \n\t" \
 309                            "push   r20                                     \n\t" \
 310                            "push   r21                                     \n\t" \
 311                            "push   r22                                     \n\t" \
 312                            "push   r23                                     \n\t" \
 313                            "push   r24                                     \n\t" \
 314                            "push   r25                                     \n\t" \
 315                            "push   r26                                     \n\t" \
 316                            "push   r27                                     \n\t" \
 317                            "push   r28                                     \n\t" \
 318                            "push   r29                                     \n\t" \
 319                            "push   r30                                     \n\t" \
 320                            "push   r31                                     \n\t" \
 321                            "lds    r26, pxCurrentTCB                       \n\t" \
 322                            "lds    r27, pxCurrentTCB + 1                   \n\t" \
 323                            "in     __tmp_reg__, __SP_L__                   \n\t" \
 324                            "st     x+, __tmp_reg__                         \n\t" \
 325                            "in     __tmp_reg__, __SP_H__                   \n\t" \
 326                            "st     x+, __tmp_reg__                         \n\t" \
 327                            );
 328 #else /* if defined( __AVR_3_BYTE_PC__ ) && defined( __AVR_HAVE_RAMPZ__ ) */
 329 /* 2-Byte PC Save */
 330     #define portSAVE_CONTEXT()                                                   \
 331     __asm__ __volatile__ ( "push   __tmp_reg__                             \n\t" \
 332                            "in     __tmp_reg__, __SREG__                   \n\t" \
 333                            "cli                                            \n\t" \
 334                            "push   __tmp_reg__                             \n\t" \
 335                            "push   __zero_reg__                            \n\t" \
 336                            "clr    __zero_reg__                            \n\t" \
 337                            "push   r2                                      \n\t" \
 338                            "push   r3                                      \n\t" \
 339                            "push   r4                                      \n\t" \
 340                            "push   r5                                      \n\t" \
 341                            "push   r6                                      \n\t" \
 342                            "push   r7                                      \n\t" \
 343                            "push   r8                                      \n\t" \
 344                            "push   r9                                      \n\t" \
 345                            "push   r10                                     \n\t" \
 346                            "push   r11                                     \n\t" \
 347                            "push   r12                                     \n\t" \
 348                            "push   r13                                     \n\t" \
 349                            "push   r14                                     \n\t" \
 350                            "push   r15                                     \n\t" \
 351                            "push   r16                                     \n\t" \
 352                            "push   r17                                     \n\t" \
 353                            "push   r18                                     \n\t" \
 354                            "push   r19                                     \n\t" \
 355                            "push   r20                                     \n\t" \
 356                            "push   r21                                     \n\t" \
 357                            "push   r22                                     \n\t" \
 358                            "push   r23                                     \n\t" \
 359                            "push   r24                                     \n\t" \
 360                            "push   r25                                     \n\t" \
 361                            "push   r26                                     \n\t" \
 362                            "push   r27                                     \n\t" \
 363                            "push   r28                                     \n\t" \
 364                            "push   r29                                     \n\t" \
 365                            "push   r30                                     \n\t" \
 366                            "push   r31                                     \n\t" \
 367                            "lds    r26, pxCurrentTCB                       \n\t" \
 368                            "lds    r27, pxCurrentTCB + 1                   \n\t" \
 369                            "in     __tmp_reg__, __SP_L__                   \n\t" \
 370                            "st     x+, __tmp_reg__                         \n\t" \
 371                            "in     __tmp_reg__, __SP_H__                   \n\t" \
 372                            "st     x+, __tmp_reg__                         \n\t" \
 373                            );
 374 #endif /* if defined( __AVR_3_BYTE_PC__ ) && defined( __AVR_HAVE_RAMPZ__ ) */
 375
 376 /*
 377  * Opposite to portSAVE_CONTEXT().  Interrupts will have been disabled during
 378  * the context save so we can write to the stack pointer.
 379  */
 380 #if defined( __AVR_3_BYTE_PC__ ) && defined( __AVR_HAVE_RAMPZ__ )
 381 /* 3-Byte PC Restore with RAMPZ */
 382     #define portRESTORE_CONTEXT()                                                \
 383     __asm__ __volatile__ ( "lds    r26, pxCurrentTCB                       \n\t" \
 384                            "lds    r27, pxCurrentTCB + 1                   \n\t" \
 385                            "ld     r28, x+                                 \n\t" \
 386                            "out    __SP_L__, r28                           \n\t" \
 387                            "ld     r29, x+                                 \n\t" \
 388                            "out    __SP_H__, r29                           \n\t" \
 389                            "pop    r31                                     \n\t" \
 390                            "pop    r30                                     \n\t" \
 391                            "pop    r29                                     \n\t" \
 392                            "pop    r28                                     \n\t" \
 393                            "pop    r27                                     \n\t" \
 394                            "pop    r26                                     \n\t" \
 395                            "pop    r25                                     \n\t" \
 396                            "pop    r24                                     \n\t" \
 397                            "pop    r23                                     \n\t" \
 398                            "pop    r22                                     \n\t" \
 399                            "pop    r21                                     \n\t" \
 400                            "pop    r20                                     \n\t" \
 401                            "pop    r19                                     \n\t" \
 402                            "pop    r18                                     \n\t" \
 403                            "pop    r17                                     \n\t" \
 404                            "pop    r16                                     \n\t" \
 405                            "pop    r15                                     \n\t" \
 406                            "pop    r14                                     \n\t" \
 407                            "pop    r13                                     \n\t" \
 408                            "pop    r12                                     \n\t" \
 409                            "pop    r11                                     \n\t" \
 410                            "pop    r10                                     \n\t" \
 411                            "pop    r9                                      \n\t" \
 412                            "pop    r8                                      \n\t" \
 413                            "pop    r7                                      \n\t" \
 414                            "pop    r6                                      \n\t" \
 415                            "pop    r5                                      \n\t" \
 416                            "pop    r4                                      \n\t" \
 417                            "pop    r3                                      \n\t" \
 418                            "pop    r2                                      \n\t" \
 419                            "pop    __zero_reg__                            \n\t" \
 420                            "pop    __tmp_reg__                             \n\t" \
 421                            "out    0x3C, __tmp_reg__                       \n\t" \
 422                            "pop    __tmp_reg__                             \n\t" \
 423                            "out    0x3B, __tmp_reg__                       \n\t" \
 424                            "pop    __tmp_reg__                             \n\t" \
 425                            "out    __SREG__, __tmp_reg__                   \n\t" \
 426                            "pop    __tmp_reg__                             \n\t" \
 427                            );
 428 #elif defined( __AVR_HAVE_RAMPZ__ )
 429 /* 2-Byte PC Restore with RAMPZ */
 430     #define portRESTORE_CONTEXT()                                                \
 431     __asm__ __volatile__ ( "lds    r26, pxCurrentTCB                       \n\t" \
 432                            "lds    r27, pxCurrentTCB + 1                   \n\t" \
 433                            "ld     r28, x+                                 \n\t" \
 434                            "out    __SP_L__, r28                           \n\t" \
 435                            "ld     r29, x+                                 \n\t" \
 436                            "out    __SP_H__, r29                           \n\t" \
 437                            "pop    r31                                     \n\t" \
 438                            "pop    r30                                     \n\t" \
 439                            "pop    r29                                     \n\t" \
 440                            "pop    r28                                     \n\t" \
 441                            "pop    r27                                     \n\t" \
 442                            "pop    r26                                     \n\t" \
 443                            "pop    r25                                     \n\t" \
 444                            "pop    r24                                     \n\t" \
 445                            "pop    r23                                     \n\t" \
 446                            "pop    r22                                     \n\t" \
 447                            "pop    r21                                     \n\t" \
 448                            "pop    r20                                     \n\t" \
 449                            "pop    r19                                     \n\t" \
 450                            "pop    r18                                     \n\t" \
 451                            "pop    r17                                     \n\t" \
 452                            "pop    r16                                     \n\t" \
 453                            "pop    r15                                     \n\t" \
 454                            "pop    r14                                     \n\t" \
 455                            "pop    r13                                     \n\t" \
 456                            "pop    r12                                     \n\t" \
 457                            "pop    r11                                     \n\t" \
 458                            "pop    r10                                     \n\t" \
 459                            "pop    r9                                      \n\t" \
 460                            "pop    r8                                      \n\t" \
 461                            "pop    r7                                      \n\t" \
 462                            "pop    r6                                      \n\t" \
 463                            "pop    r5                                      \n\t" \
 464                            "pop    r4                                      \n\t" \
 465                            "pop    r3                                      \n\t" \
 466                            "pop    r2                                      \n\t" \
 467                            "pop    __zero_reg__                            \n\t" \
 468                            "pop    __tmp_reg__                             \n\t" \
 469                            "out    0x3B, __tmp_reg__                       \n\t" \
 470                            "pop    __tmp_reg__                             \n\t" \
 471                            "out    __SREG__, __tmp_reg__                   \n\t" \
 472                            "pop    __tmp_reg__                             \n\t" \
 473                            );
 474 #else /* if defined( __AVR_3_BYTE_PC__ ) && defined( __AVR_HAVE_RAMPZ__ ) */
 475 /* 2-Byte PC Restore */
 476     #define portRESTORE_CONTEXT()                                                \
 477     __asm__ __volatile__ ( "lds    r26, pxCurrentTCB                       \n\t" \
 478                            "lds    r27, pxCurrentTCB + 1                   \n\t" \
 479                            "ld     r28, x+                                 \n\t" \
 480                            "out    __SP_L__, r28                           \n\t" \
 481                            "ld     r29, x+                                 \n\t" \
 482                            "out    __SP_H__, r29                           \n\t" \
 483                            "pop    r31                                     \n\t" \
 484                            "pop    r30                                     \n\t" \
 485                            "pop    r29                                     \n\t" \
 486                            "pop    r28                                     \n\t" \
 487                            "pop    r27                                     \n\t" \
 488                            "pop    r26                                     \n\t" \
 489                            "pop    r25                                     \n\t" \
 490                            "pop    r24                                     \n\t" \
 491                            "pop    r23                                     \n\t" \
 492                            "pop    r22                                     \n\t" \
 493                            "pop    r21                                     \n\t" \
 494                            "pop    r20                                     \n\t" \
 495                            "pop    r19                                     \n\t" \
 496                            "pop    r18                                     \n\t" \
 497                            "pop    r17                                     \n\t" \
 498                            "pop    r16                                     \n\t" \
 499                            "pop    r15                                     \n\t" \
 500                            "pop    r14                                     \n\t" \
 501                            "pop    r13                                     \n\t" \
 502                            "pop    r12                                     \n\t" \
 503                            "pop    r11                                     \n\t" \
 504                            "pop    r10                                     \n\t" \
 505                            "pop    r9                                      \n\t" \
 506                            "pop    r8                                      \n\t" \
 507                            "pop    r7                                      \n\t" \
 508                            "pop    r6                                      \n\t" \
 509                            "pop    r5                                      \n\t" \
 510                            "pop    r4                                      \n\t" \
 511                            "pop    r3                                      \n\t" \
 512                            "pop    r2                                      \n\t" \
 513                            "pop    __zero_reg__                            \n\t" \
 514                            "pop    __tmp_reg__                             \n\t" \
 515                            "out    __SREG__, __tmp_reg__                   \n\t" \
 516                            "pop    __tmp_reg__                             \n\t" \
 517                            );
 518 #endif /* if defined( __AVR_3_BYTE_PC__ ) && defined( __AVR_HAVE_RAMPZ__ ) */
 519 /*-----------------------------------------------------------*/
 520
 521 /*
 522  * Perform hardware setup to enable ticks from relevant Timer.
 523  */
 524 static void prvSetupTimerInterrupt( void );
 525 /*-----------------------------------------------------------*/
 526
 527 /*
 528  * See header file for description.
 529  */
 530 StackType_t * pxPortInitialiseStack( StackType_t * pxTopOfStack,
 531                                      TaskFunction_t pxCode,
 532                                      void * pvParameters )
 533 {
 534     uint16_t usAddress;
 535
 536     /* Simulate how the stack would look after a call to vPortYield() generated by
 537      * the compiler. */
 538
 539     /* The start of the task code will be popped off the stack last, so place
 540      * it on first. */
 541     usAddress = ( uint16_t ) pxCode;
 542     *pxTopOfStack = ( StackType_t ) ( usAddress & ( uint16_t ) 0x00ff );
 543     pxTopOfStack--;
 544
 545     usAddress >>= 8;
 546     *pxTopOfStack = ( StackType_t ) ( usAddress & ( uint16_t ) 0x00ff );
 547     pxTopOfStack--;
 548
 549     #if defined( __AVR_3_BYTE_PC__ )
 550
 551         /* The AVR ATmega2560/ATmega2561 have 256KBytes of program memory and a 17-bit
 552          * program counter. When a code address is stored on the stack, it takes 3 bytes
 553          * instead of 2 for the other ATmega* chips.
 554          *
 555          * Store 0 as the top byte since we force all task routines to the bottom 128K
 556          * of flash. We do this by using the .lowtext label in the linker script.
 557          *
 558          * In order to do this properly, we would need to get a full 3-byte pointer to
 559          * pxCode. That requires a change to GCC. Not likely to happen any time soon.
 560          */
 561         *pxTopOfStack = 0;
 562         pxTopOfStack--;
 563     #endif
 564
 565     /* Next simulate the stack as if after a call to portSAVE_CONTEXT().
 566      *  portSAVE_CONTEXT places the flags on the stack immediately after r0
 567      *  to ensure the interrupts get disabled as soon as possible, and so ensuring
 568      *  the stack use is minimal should a context switch interrupt occur. */
 569     *pxTopOfStack = ( StackType_t ) 0x00; /* R0 */
 570     pxTopOfStack--;
 571     *pxTopOfStack = portFLAGS_INT_ENABLED;
 572     pxTopOfStack--;
 573
 574     #if defined( __AVR_3_BYTE_PC__ )
 575
 576         /* If we have an ATmega256x, we are also saving the EIND register.
 577          * We should default to 0.
 578          */
 579         *pxTopOfStack = ( StackType_t ) 0x00; /* EIND */
 580         pxTopOfStack--;
 581     #endif
 582
 583     #if defined( __AVR_HAVE_RAMPZ__ )
 584
 585         /* We are saving the RAMPZ register.
 586          * We should default to 0.
 587          */
 588         *pxTopOfStack = ( StackType_t ) 0x00; /* RAMPZ */
 589         pxTopOfStack--;
 590     #endif
 591
 592     /* Now the remaining registers. The compiler expects R1 to be 0. */
 593     *pxTopOfStack = ( StackType_t ) 0x00; /* R1 */
 594
 595     /* Leave R2 - R23 untouched */
 596     pxTopOfStack -= 23;
 597
 598     /* Place the parameter on the stack in the expected location. */
 599     usAddress = ( uint16_t ) pvParameters;
 600     *pxTopOfStack = ( StackType_t ) ( usAddress & ( uint16_t ) 0x00ff );
 601     pxTopOfStack--;
 602
 603     usAddress >>= 8;
 604     *pxTopOfStack = ( StackType_t ) ( usAddress & ( uint16_t ) 0x00ff );
 605
 606     /* Leave register R26 - R31 untouched */
 607     pxTopOfStack -= 7;
 608
 609     return pxTopOfStack;
 610 }
 611 /*-----------------------------------------------------------*/
 612
 613 BaseType_t xPortStartScheduler( void )
 614 {
 615     /* Setup the relevant timer hardware to generate the tick. */
 616     prvSetupTimerInterrupt();
 617
 618     /* Restore the context of the first task that is going to run. */
 619     portRESTORE_CONTEXT();
 620
 621     /* Simulate a function call end as generated by the compiler. We will now
 622      * jump to the start of the task the context of which we have just restored. */
 623     __asm__ __volatile__ ( "ret" );
 624
 625     /* Should not get here. */
 626     return pdTRUE;
 627 }
 628 /*-----------------------------------------------------------*/
 629
 630 void vPortEndScheduler( void )
 631 {
 632     /* It is unlikely that the ATmega port will get stopped. */
 633 }
 634 /*-----------------------------------------------------------*/
 635
 636 /*
 637  * Manual context switch. The first thing we do is save the registers so we
 638  * can use a naked attribute.
 639  */
 640 void vPortYield( void ) __attribute__( ( hot, flatten, naked ) );
 641 void vPortYield( void )
 642 {
 643     portSAVE_CONTEXT();
 644     vTaskSwitchContext();
 645     portRESTORE_CONTEXT();
 646
 647     __asm__ __volatile__ ( "ret" );
 648 }
 649 /*-----------------------------------------------------------*/
 650
 651 /*
 652  * Manual context switch callable from ISRs. The first thing we do is save
 653  * the registers so we can use a naked attribute.
 654  */
 655 void vPortYieldFromISR( void ) __attribute__( ( hot, flatten, naked ) );
 656 void vPortYieldFromISR( void )
 657 {
 658     portSAVE_CONTEXT();
 659     vTaskSwitchContext();
 660     portRESTORE_CONTEXT();
 661
 662     __asm__ __volatile__ ( "reti" );
 663 }
 664 /*-----------------------------------------------------------*/
 665
 666 /*
 667  * Context switch function used by the tick. This must be identical to
 668  * vPortYield() from the call to vTaskSwitchContext() onwards. The only
 669  * difference from vPortYield() is the tick count is incremented as the
 670  * call comes from the tick ISR.
 671  */
 672 void vPortYieldFromTick( void ) __attribute__( ( hot, flatten, naked ) );
 673 void vPortYieldFromTick( void )
 674 {
 675     portSAVE_CONTEXT();
 676
 677     if( xTaskIncrementTick() != pdFALSE )
 678     {
 679         vTaskSwitchContext();
 680     }
 681
 682     portRESTORE_CONTEXT();
 683
 684     __asm__ __volatile__ ( "ret" );
 685 }
 686 /*-----------------------------------------------------------*/
 687
 688 #if defined( portUSE_WDTO )
 689
 690 /*
 691  * Setup WDT to generate a tick interrupt.
 692  */
 693     void prvSetupTimerInterrupt( void )
 694     {
 695         /* reset watchdog */
 696         wdt_reset();
 697
 698         /* set up WDT Interrupt (rather than the WDT Reset). */
 699         wdt_interrupt_enable( portUSE_WDTO );
 700     }
 701
 702 #elif defined( portUSE_TIMER0 )
 703
 704 /*
 705  * Setup Timer0 compare match A to generate a tick interrupt.
 706  */
 707     static void prvSetupTimerInterrupt( void )
 708     {
 709         uint32_t ulCompareMatch;
 710         uint8_t ucLowByte;
 711
 712         /* Using 8bit Timer0 to generate the tick. Correct fuses must be
 713          * selected for the configCPU_CLOCK_HZ clock.*/
 714
 715         ulCompareMatch = configCPU_CLOCK_HZ / configTICK_RATE_HZ;
 716
 717         /* We only have 8 bits so have to scale 1024 to get our required tick rate. */
 718         ulCompareMatch /= portCLOCK_PRESCALER;
 719
 720         /* Adjust for correct value. */
 721         ulCompareMatch -= ( uint32_t ) 1;
 722
 723         /* Setup compare match value for compare match A. Interrupts are disabled
 724          * before this is called so we need not worry here. */
 725         ucLowByte = ( uint8_t ) ( ulCompareMatch & ( uint32_t ) 0xff );
 726         portOCRL = ucLowByte;
 727
 728         /* Setup clock source and compare match behaviour. */
 729         portTCCRa = portCLEAR_COUNTER_ON_MATCH;
 730         portTCCRb = portPRESCALE_1024;
 731
 732
 733         /* Enable the interrupt - this is okay as interrupt are currently globally disabled. */
 734         ucLowByte = portTIMSK;
 735         ucLowByte |= portCOMPARE_MATCH_A_INTERRUPT_ENABLE;
 736         portTIMSK = ucLowByte;
 737     }
 738
 739 #endif /* if defined( portUSE_WDTO ) */
 740
 741 /*-----------------------------------------------------------*/
 742
 743 #if configUSE_PREEMPTION == 1
 744
 745 /*
 746  * Tick ISR for preemptive scheduler. We can use a naked attribute as
 747  * the context is saved at the start of vPortYieldFromTick(). The tick
 748  * count is incremented after the context is saved.
 749  *
 750  * use ISR_NOBLOCK where there is an important timer running, that should preempt the scheduler.
 751  *
 752  */
 753     ISR( portSCHEDULER_ISR, ISR_NAKED ) __attribute__( ( hot, flatten ) );
 754
 755 /*  ISR(portSCHEDULER_ISR, ISR_NAKED ISR_NOBLOCK) __attribute__ ((hot, flatten));
 756  */
 757     ISR( portSCHEDULER_ISR )
 758     {
 759         vPortYieldFromTick();
 760         __asm__ __volatile__ ( "reti" );
 761     }
 762 #else /* if configUSE_PREEMPTION == 1 */
 763
 764 /*
 765  * Tick ISR for the cooperative scheduler. All this does is increment the
 766  * tick count. We don't need to switch context, this can only be done by
 767  * manual calls to taskYIELD();
 768  *
 769  * use ISR_NOBLOCK where there is an important timer running, that should preempt the scheduler.
 770  */
 771     ISR( portSCHEDULER_ISR ) __attribute__( ( hot, flatten ) );
 772
 773 /*  ISR(portSCHEDULER_ISR, ISR_NOBLOCK) __attribute__ ((hot, flatten));
 774  */
 775     ISR( portSCHEDULER_ISR )
 776     {
 777         xTaskIncrementTick();
 778     }
 779 #endif /* if configUSE_PREEMPTION == 1 */