sdcc/device/lib/mos6502/crt0.s

   1 ;--------------------------------------------------------------------------
   2 ;  crt0.s - Generic crt0.s for a bare metal 6502
   3 ;
   4 ;  Copyright (C) 2021-2023, Gabriele Gorla
   5 ;  Copyright (C) 2023, Maarten Brock
   6 ;
   7 ;  This library is free software; you can redistribute it and/or modify it
   8 ;  under the terms of the GNU General Public License as published by the
   9 ;  Free Software Foundation; either version 2, or (at your option) any
  10 ;  later version.
  11 ;
  12 ;  This library is distributed in the hope that it will be useful,
  13 ;  but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 ;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  15 ;  GNU General Public License for more details.
  16 ;
  17 ;  You should have received a copy of the GNU General Public License
  18 ;  along with this library; see the file COPYING. If not, write to the
  19 ;  Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
  20 ;   MA 02110-1301, USA.
  21 ;
  22 ;  As a special exception, if you link this library with other files,
  23 ;  some of which are compiled with SDCC, to produce an executable,
  24 ;  this library does not by itself cause the resulting executable to
  25 ;  be covered by the GNU General Public License. This exception does
  26 ;  not however invalidate any other reasons why the executable file
  27 ;   might be covered by the GNU General Public License.
  28 ;--------------------------------------------------------------------------
  29
  30         .module crt0
  31
  32         ;; Ordering of segments for the linker.
  33         .area ZP      (PAG)
  34         .area OSEG    (PAG, OVR)
  35
  36         .area _DATA
  37         .area DATA
  38         .area BSS
  39
  40         .area _CODE
  41         .area GSINIT
  42         .area GSFINAL
  43         .area CODE
  44         .area RODATA
  45         .area XINIT
  46
  47         ;; Reset/interrupt vectors
  48         .area CODEIVT (ABS)
  49         .org  0xfffa
  50         .dw     __sdcc_gs_init_startup ; NMI
  51         .dw     __sdcc_gs_init_startup ; RESET
  52         .dw     __sdcc_gs_init_startup ; IRQ/BRK
  53
  54         .area GSINIT
  55 __sdcc_gs_init_startup:
  56         ldx     #0xff
  57         txs
  58 ;       ldx     #0x01         ; MSB of stack ptr
  59 ;       stx     __BASEPTR+1
  60
  61 ;; Skip initialisation of global variables if __sdcc_external_startup
  62 ;; returned non-zero value.
  63         jsr     ___sdcc_external_startup
  64         ora     #0
  65         beq     __sdcc_init_data
  66         jmp     __sdcc_program_startup
  67
  68 __sdcc_init_data:
  69 ;; clear ZP
  70         lda     #0x00
  71         ldx     #<s_ZP
  72         ldy     #<l_ZP
  73         beq     00101$
  74 00100$:
  75         sta     *0,X
  76         inx
  77         dey
  78         bne     00100$
  79 00101$:
  80
  81 ;; initialize DATA
  82         lda     #>l_XINIT
  83         sta     *___memcpy_PARM_3+1
  84         lda     #<l_XINIT
  85         sta     *___memcpy_PARM_3
  86         lda     #>s_XINIT
  87         sta     *___memcpy_PARM_2+1
  88         lda     #<s_XINIT
  89         sta     *___memcpy_PARM_2
  90         lda     #<s_DATA
  91         ldx     #>s_DATA
  92         jsr     ___memcpy
  93
  94 ;; clear BSS
  95         lda     #>l_BSS
  96         sta     *_memset_PARM_3+1
  97         lda     #<l_BSS
  98         sta     *_memset_PARM_3
  99         lda     #0x00
 100         sta     *_memset_PARM_2
 101         lda     #<s_BSS
 102         ldx     #>s_BSS
 103         jsr     _memset
 104
 105         .area GSFINAL
 106 __sdcc_program_startup:
 107         jsr     _main
 108         jmp     .
 109