boot.s

GBA游戏程序

@********************************************************************
@*   crt0.S v1.26 by Jeff Frohwein                                  *
@********************************************************************

@ v1.0 - Original release
@ v1.1 - Added proper .data section support
@ v1.2 - Added support for c++, overlays, interrupts, and
@        far calls (__FarFunction & __FarProcedure).
@      - Some ideas from Jason Wilkins & Mike Heckenbach.
@ v1.21- Killed the dumb test bug left in the code.
@ v1.22- Killed dumb bug "numero dos" in multiple interrupts routine. Thanks Mike H. :)
@ v1.23- Now correctly handles zero length .bss section.
@ v1.24- Loop back to start_vector now works if main {} exits.
@ v1.25- __FarProcedure now works. It was missing a .thumb_func directive.
@ v1.26- Added missing Serial Interrupt processing to __MultipleInterrupts section.
@        Added __FastInterrupt option for minimal interrupt processing.
@        Optimized __MultipleInterrupts section to save 4 bytes of stack space.
@        Added __ISRinIWRAM option that puts interrupt processing in IWRAM by default.
@        Options passed to main() or AgbMain() are now set to 0. (Thanks to DarkFader)
@
@ This file is released into the public domain for commercial
@ or non-commercial usage with no restrictions placed upon it.

    .TEXT

@ Comment out the next line ONLY if you plan to never support
@ multiboot mode and want to save a few bytes by removing
@ multiboot support code. Otherwise, leave it alone. It wont
@ disturb code designed to run only on flash carts.
@
@ The normal way to enable generating code that works with
@ both multiboot and flash carts is to add the following to
@ your C code in your main project file AS A GLOBAL VARIABLE:
@
@   #define MULTIBOOT int __gba_multiboot;
@ Then use it like this : MULTIBOOT
@
@ IT MUST BE A GLOBAL VARIABLE OR IT WILL NOT WORK!
@ If this variable is not defined somewhere in your project
@ then code will be generated to run out of ROM instead of
@ EXRAM. The value of this variable is not important.

 .equ __MultiBootInclude, 1

@ If you are compiling for multiboot dedicated (will not
@ run in a cart) code then uncomment the following. Normally
@ you should leave this commented out so that a multiboot
@ image will run in a cart as well (by copying from ROM to RAM).
@
@ This sets the maker code to "MB  " which is a key that
@ some emulators look for to know to load the rom image
@ at 0x2000000 instead of the standard 0x8000000.

@ .equ __MultibootDedicated, 1

@ There are two methods for clearing memory and
@ copying appropriate setup data. The fast & bulky
@ method is GBA DMA copy/clear but some emulators
@ do not accurately do DMA. If you have an inaccurate
@ emulator or want to conserve ROM space then comment
@ out the following line. There is not much advantage
@ gained by doing DMA copy/clear.

@ .equ __DMACopyClear, 1

@ Uncomment the following line to support C++ development.
@ You also need to name your main C function the following:
@    int main (void)  ...instead of... int AgbMain (void)
@ Doing so will cause ~5500 bytes of c++ support code to be
@ linked in with your project so do not enable c++ support
@ unless you plan to use it.

@ .equ __CPPSupport, 1

@ Comment out the following line to disable interrupt support
@ in your code and to save some space in this file.

@ .equ __InterruptSupport, 1


@ Comment out the following line to put interrupt support in
@ ROM instead of IWRAM. Interrupt support in ROM will slow
@ down interrupt execution and has no advantage other than
@ saving a little bit of IWRAM.

 .equ __ISRinIWRAM, 1

@ NOTE: Only ONE of the following 3 interrupt options may be
@ uncommented. Also, __InterruptSupport above must be uncommented
@ for any of the following to have an effect.
@
@ __FastInterrupts
@   Uncomment this line for minimal interrupt processing.
@
@ __SingleInterrupts
@   Uncomment this line if you wish to use a table of function
@   pointers to process specific interrupts.
@
@ __MultipleInterrupts
@   Uncomment this line to allow multiple-interrupts-at-once
@   support. If you have several interrupts where one can
@   occur while another is being serviced then you need to
@   enable this option.

.equ __FastInterrupts, 1
@ .equ __SingleInterrupts, 1
@ .equ __MultipleInterrupts, 1


@ Uncomment the following line to disable sound and enter an
@ infinite loop if cart is removed during game play. You
@ must have the cart interrupt enabled for this to work and
@ __ISRinIWRAM, above, must be enabled (not commented out.)

@ .equ __HandleCartInterrupt, 1

@ The following prevents IRQ stack overflow by switching to
@ System mode (User stack) when handling multiple interrupts.
@ To force use of IRQ stack only, comment out the following line.

 .equ __SwitchToUserStack, 1

@ !!!! NOTE: THE COPY ROUTINES IN THIS FILE WORK ON 4 BYTE
@ BOUNDARIES. YOUR LINKER SCRIPT MUST ALIGN SECTION STARTS
@ AND SECTION ENDS FOR SECTIONS THAT GET COPIED TO RAM WITH
@ ALIGN(4) !!!!

    .GLOBAL     _start
_start:
        .ALIGN
        .CODE 32
    @ Start Vector

        b       rom_header_end

    @ Nintendo Logo Character Data (8000004h)
        .fill   156,1,0

    @ Game Title (80000A0h)
        .byte   0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
        .byte   0x00,0x00,0x00,0x00

 .ifdef __MultibootDedicated
    @ Game Code (80000ACh)
        .ascii  "MB  "
 .else
    @ Game Code (80000ACh)
        .byte   0x00,0x00,0x00,0x00
 .endif

    @ Maker Code (80000B0h)
        .byte   0x30,0x31

    @ Fixed Value (80000B2h)
        .byte   0x96

    @ Main Unit Code (80000B3h)
        .byte   0x00

    @ Device Type (80000B4h)
        .byte   0x00

    @ Unused Data (7Byte) (80000B5h)
        .byte   0x00,0x00,0x00,0x00,0x00,0x00,0x00

    @ Software Version No (80000BCh)
        .byte   0x00

    @ Complement Check (80000BDh)
        .byte   0xf0

    @ Checksum (80000BEh)
        .byte   0x00,0x00

    .ALIGN
    .ARM                                @ ..or you can use CODE 32 here

rom_header_end:
        b       start_vector        @ This branch must be here for proper
                                    @ positioning of the following header.
                                    @ DO NOT REMOVE IT.

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ The following reserved bytes are used if the code is compiled for      @
@ multiboot mode. It does not hurt anything to leave this header in
@ even if the code is not compiled for multiboot. The GBA BIOS will
@ auto-patch the first two bytes with 0x03 and 0x01, respectively,
@ before running any code if it is executed as multiboot.
@

@ The following two bytes are included even for non-multiboot supporting
@ builds to guarantee that any generic library code that depends on them
@ will still be functional.

    .GLOBAL     __boot_method, __slave_number

__boot_method:
        .byte   0       @ boot method (0=ROM boot, 3=Multiplay boot)
__slave_number:
        .byte   0       @ slave # (1=slave#1, 2=slave#2, 3=slave#3)

 .ifdef __MultiBootInclude

        .byte   0       @ reserved
        .byte   0       @ reserved
        .word   0       @ reserved
        .word   0       @ reserved
        .word   0       @ reserved
        .word   0       @ reserved
        .word   0       @ reserved
        .word   0       @ reserved
 .endif
@                                                                        @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@


@@@@@@@@@@@@@@@@@@@@@@
@        Reset       @
@@@@@@@@@@@@@@@@@@@@@@

    .GLOBAL     start_vector
    .ALIGN
    .ARM                                @ ..or you can use CODE 32 here
start_vector:
        mov     r0, #0x12               @ Switch to IRQ Mode
        msr     cpsr, r0
        ldr     sp,=__sp_irq            @ Set SP_irq
        mov     r0, #0x1f               @ Switch to System Mode
        msr     cpsr, r0
        ldr     sp,=__sp_usr            @ Set SP_usr

@ Enter Thumb mode
        adr    r0,1f + 1                @ add r0,pc,#1 also works here
                                        @  for those that want to conserve labels.
        bx     r0

        .THUMB                          @ ..or you can use .CODE 16 here
1:

 .ifdef __InterruptSupport
        ldr     r1, =__intr_vector_buf  @ Set Interrupt Address
        ldr     r0, =intr_main
        str     r0, [r1]
 .endif

 .ifdef __MultiBootInclude

@ *** Multiboot Copy Routine ***
@   Check the Program Counter to see if code is running
@ at 0x2000000 or 0x8000000. If it is running at 0x8000000
@ then copy 256K bytes of it to 0x2000000 and then branch
@ to 0x2000000.
@   The reason for all this is to allow a program to be used
@ "as is" with an flash cart/emulator or with an MBV2-style
@ multiboot cable.
@   NOTE: You can also detect if this ROM is running from
@ 0x2000000 by checking the multiboot header above.

        ldr     r0,=__text_start
        lsl     r0,#5           @ Was code compiled at 0x08000000 or higher?
        bcs     DoEWRAMClear    @ yes, you can not run it in external WRAM

@ Make sure we're in ExWRAM

        mov     r0,pc
        lsl     r0,#5           @ Are we running from ROM (0x8000000 or higher) ?
        bcc     SkipEWRAMClear  @ No, so no need to do a copy.

@ We were started in ROM, silly emulators. :P
@ So we need to copy to ExWRAM.

        mov     r3,#0x40
        lsl     r3,#12          @ r3 = 0x40000
        lsl     r2,r3,#7        @ r2 = 0x2000000
        mov     r6,r2           @ r6 = 0x2000000
        lsl     r1,r2,#2        @ r1 = 0x8000000

        bl      CopyMem

@ Jump to the code to execute

        bx      r6
 .endif

DoEWRAMClear:
@ Clear External WRAM to 0x00

        mov     r1,#0x40
        lsl     r1,#12          @ r1 = 0x40000
        lsl     r0,r1,#7        @ r0 = 0x2000000
        bl      ClearMem

SkipEWRAMClear:
@        ldr     r0,=AgbMain
@        bx r0

@ Clear Internal WRAM to 0x00
        mov     r0,#3
        lsl     r0,#24          @ r0 = 0x3000000
        ldr     r1,=__sp_usr_offset - 16
        bl      ClearMem

 .ifdef __MultiBootInclude
@ Clear BSS section to 0x00
@ (Sometimes BSS may be in External WRAM)
        ldr     r0,=__bss_start
        ldr     r1,=__bss_end
        sub     r1,r0
        bl      ClearMem
 .endif

@ Copy initialized data (data section) from LMA to VMA (ROM to RAM)
        ldr     r1,=__data_lma
        ldr     r2,=__data_start
        ldr     r4,=__data_end
        bl      CopyMemChk

@ Copy internal work ram (iwram section) from LMA to VMA (ROM to RAM)
        ldr     r1,=__iwram_lma
        ldr     r2,=__iwram_start
        ldr     r4,=__iwram_end
        bl      CopyMemChk

@ Copy internal work ram overlay 0 (iwram0 section) from LMA to VMA (ROM to RAM)
        ldr     r2,=__load_stop_iwram0
        ldr     r1,=__load_start_iwram0
        sub     r3,r2,r1         @ Is there any data to copy?
        beq     CIW0Skip         @ no

        ldr     r2,=__iwram_overlay_start