simple-FreeRTOS-demo/boot.s

   1         /* Sample initialization file */
   2
   3         .extern main
   4         .extern exit
   5
   6         .text
   7         .code 32
   8
   9
  10         .align  0
  11
  12         .extern __bss_beg__
  13         .extern __bss_end__
  14         .extern __stack_end__
  15         .extern __data_beg__
  16         .extern __data_end__
  17         .extern __data+beg_src__
  18
  19         .global start
  20         .global endless_loop
  21
  22         /* Stack Sizes */
  23     .set  UND_STACK_SIZE, 0x00000004
  24     .set  ABT_STACK_SIZE, 0x00000004
  25     .set  FIQ_STACK_SIZE, 0x00000004
  26     .set  IRQ_STACK_SIZE, 0X00000400
  27     .set  SVC_STACK_SIZE, 0x00000400
  28
  29         /* Standard definitions of Mode bits and Interrupt (I & F) flags in PSRs */
  30     .set  MODE_USR, 0x10            /* User Mode */
  31     .set  MODE_FIQ, 0x11            /* FIQ Mode */
  32     .set  MODE_IRQ, 0x12            /* IRQ Mode */
  33     .set  MODE_SVC, 0x13            /* Supervisor Mode */
  34     .set  MODE_ABT, 0x17            /* Abort Mode */
  35     .set  MODE_UND, 0x1B            /* Undefined Mode */
  36     .set  MODE_SYS, 0x1F            /* System Mode */
  37
  38     .equ  I_BIT, 0x80               /* when I bit is set, IRQ is disabled */
  39     .equ  F_BIT, 0x40               /* when F bit is set, FIQ is disabled */
  40
  41
  42 start:
  43 _start:
  44 _mainCRTStartup:
  45
  46         /* Setup a stack for each mode - note that this only sets up a usable stack
  47         for system/user, SWI and IRQ modes.   Also each mode is setup with
  48         interrupts initially disabled. */
  49     ldr   r0, .LC6
  50     msr   CPSR_c, #MODE_UND|I_BIT|F_BIT /* Undefined Instruction Mode */
  51     mov   sp, r0
  52     sub   r0, r0, #UND_STACK_SIZE
  53     msr   CPSR_c, #MODE_ABT|I_BIT|F_BIT /* Abort Mode */
  54     mov   sp, r0
  55     sub   r0, r0, #ABT_STACK_SIZE
  56     msr   CPSR_c, #MODE_FIQ|I_BIT|F_BIT /* FIQ Mode */
  57     mov   sp, r0
  58     sub   r0, r0, #FIQ_STACK_SIZE
  59     msr   CPSR_c, #MODE_IRQ|I_BIT|F_BIT /* IRQ Mode */
  60     mov   sp, r0
  61     sub   r0, r0, #IRQ_STACK_SIZE
  62     msr   CPSR_c, #MODE_SVC|I_BIT|F_BIT /* Supervisor Mode */
  63     mov   sp, r0
  64     sub   r0, r0, #SVC_STACK_SIZE
  65     msr   CPSR_c, #MODE_SYS|I_BIT|F_BIT /* System Mode */
  66     mov   sp, r0
  67
  68         /* We want to start in supervisor mode.  Operation will switch to system
  69         mode when the first task starts. */
  70         msr   CPSR_c, #MODE_SVC|I_BIT|F_BIT
  71
  72         /* Clear BSS. */
  73
  74         mov     a2, #0                  /* Fill value */
  75         mov             fp, a2                  /* Null frame pointer */
  76         mov             r7, a2                  /* Null frame pointer for Thumb */
  77
  78         ldr             r1, .LC1                /* Start of memory block */
  79         ldr             r3, .LC2                /* End of memory block */
  80         subs    r3, r3, r1      /* Length of block */
  81         beq             .end_clear_loop
  82         mov             r2, #0
  83
  84 .clear_loop:
  85         strb    r2, [r1], #1
  86         subs    r3, r3, #1
  87         bgt             .clear_loop
  88
  89 .end_clear_loop:
  90
  91         /* Initialise data. */
  92
  93         ldr             r1, .LC3                /* Start of memory block */
  94         ldr             r2, .LC4                /* End of memory block */
  95         ldr             r3, .LC5
  96         subs    r3, r3, r1              /* Length of block */
  97         beq             .end_set_loop
  98
  99 .set_loop:
 100         ldrb    r4, [r2], #1
 101         strb    r4, [r1], #1
 102         subs    r3, r3, #1
 103         bgt             .set_loop
 104
 105 .end_set_loop:
 106
 107         mov             r0, #0          /* no arguments  */
 108         mov             r1, #0          /* no argv either */
 109
 110         bl              main
 111
 112 endless_loop:
 113         b               endless_loop
 114
 115
 116         .align 0
 117
 118         .LC1:
 119         .word   __bss_beg__
 120         .LC2:
 121         .word   __bss_end__
 122         .LC3:
 123         .word   __data_beg__
 124         .LC4:
 125         .word   __data_beg_src__
 126         .LC5:
 127         .word   __data_end__
 128         .LC6:
 129         .word   __stack_end__
 130
 131
 132         /* Setup vector table.  Note that undf, pabt, dabt, fiq just execute
 133         a null loop. */
 134
 135 .section .startup,"ax"
 136          .code 32
 137          .align 0
 138
 139         b     _start                                            /* reset - _start                       */
 140         ldr   pc, _undf                                         /* undefined - _undf            */
 141         ldr   pc, _swi                                          /* SWI - _swi                           */
 142         ldr   pc, _pabt                                         /* program abort - _pabt        */
 143         ldr   pc, _dabt                                         /* data abort - _dabt           */
 144         nop                                                                     /* reserved                                     */
 145         ldr   pc, [pc,#-0xFF0]                          /* IRQ - read the VIC           */
 146         ldr   pc, _fiq                                          /* FIQ - _fiq                           */
 147
 148 _undf:  .word __undf                    /* undefined                            */
 149 _swi:   .word vPortYieldProcessor       /* SWI                                          */
 150 _pabt:  .word __pabt                    /* program abort                        */
 151 _dabt:  .word __dabt                    /* data abort                           */
 152 _fiq:   .word __fiq                     /* FIQ                                          */
 153
 154 __undf: b     .                         /* undefined                            */
 155 __pabt: b     .                         /* program abort                        */
 156 __dabt: b     .                         /* data abort                           */
 157 __fiq:  b     .                         /* FIQ                                          */