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gba_crt0.s
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gba_crt0.s
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.section ".init"
.global _start
.align
.arm
@---------------------------------------------------------------------------------
_start:
@---------------------------------------------------------------------------------
b rom_header_end
.fill 156,1,0 @ Nintendo Logo Character Data (8000004h)
.fill 16,1,0 @ Game Title
.byte 0x30,0x31 @ Maker Code (80000B0h)
.byte 0x96 @ Fixed Value (80000B2h)
.byte 0x00 @ Main Unit Code (80000B3h)
.byte 0x00 @ Device Type (80000B4h)
.fill 7,1,0 @ unused
.byte 0x00 @ Software Version No (80000BCh)
.byte 0xf0 @ Complement Check (80000BDh)
.byte 0x00,0x00 @ Checksum (80000BEh)
@---------------------------------------------------------------------------------
rom_header_end:
@---------------------------------------------------------------------------------
b start_vector @ This branch must be here for proper
@ positioning of the following header.
.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)
.byte 0 @ reserved
.byte 0 @ reserved
.word 0 @ reserved
.word 0 @ reserved
.word 0 @ reserved
.word 0 @ reserved
.word 0 @ reserved
.word 0 @ reserved
.global start_vector
.align
@---------------------------------------------------------------------------------
start_vector:
@---------------------------------------------------------------------------------
mov r0, #0x4000000 @ REG_BASE
str r0, [r0, #0x208]
mov r0, #0x12 @ Switch to IRQ Mode
msr cpsr, r0
ldr sp, =__sp_irq @ Set IRQ stack
mov r0, #0x1f @ Switch to System Mode
msr cpsr, r0
ldr sp, =__sp_usr @ Set user stack
@---------------------------------------------------------------------------------
@ Enter Thumb mode
@---------------------------------------------------------------------------------
add r0, pc, #1
bx r0
.thumb
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
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 r2, #2
lsl r2, r2, #24 @ r2= 0x02000000
ldr r3, =__end__ @ last ewram address
sub r3, r2 @ r3= actual binary size
mov r6, r2 @ r6= 0x02000000
lsl r1, r2, #2 @ r1= 0x08000000
bl CopyMem
bx r6 @ Jump to the code to execute
@---------------------------------------------------------------------------------
DoEWRAMClear: @ Clear External WRAM to 0x00
@---------------------------------------------------------------------------------
mov r1, #0x40
lsl r1, #12 @ r1 = 0x40000
lsl r0, r1, #7 @ r0 = 0x2000000
bl ClearMem
@---------------------------------------------------------------------------------
SkipEWRAMClear: @ Clear Internal WRAM to 0x00
@---------------------------------------------------------------------------------
@---------------------------------------------------------------------------------
@ Clear BSS section to 0x00
@---------------------------------------------------------------------------------
ldr r0, =__bss_start__
ldr r1, =__bss_end__
sub r1, r0
bl ClearMem
@---------------------------------------------------------------------------------
@ Clear SBSS section to 0x00
@---------------------------------------------------------------------------------
ldr r0, =__sbss_start__
ldr r1, =__sbss_end__
sub r1, r0
bl ClearMem
@---------------------------------------------------------------------------------
@ 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
bl CopyMem
@---------------------------------------------------------------------------------
CIW0Skip:
@---------------------------------------------------------------------------------
@ Copy external work ram (ewram section) from LMA to VMA (ROM to RAM)
@---------------------------------------------------------------------------------
ldr r1, =__ewram_lma
ldr r2, =__ewram_start
ldr r4, =__ewram_end
bl CopyMemChk
@---------------------------------------------------------------------------------
CEW0Skip:
@---------------------------------------------------------------------------------
@ set heap end
@---------------------------------------------------------------------------------
ldr r1, =fake_heap_end
ldr r0, =__eheap_end
str r0, [r1]
@---------------------------------------------------------------------------------
@ global constructors
@---------------------------------------------------------------------------------
ldr r3, =__libc_init_array
bl _blx_r3_stub
@---------------------------------------------------------------------------------
@ Jump to user code
@---------------------------------------------------------------------------------
mov r0, #0 @ int argc
mov r1, #0 @ char *argv[]
ldr r3, =main
bl _blx_r3_stub
@---------------------------------------------------------------------------------
@ Clear memory to 0x00 if length != 0
@---------------------------------------------------------------------------------
@ r0 = Start Address
@ r1 = Length
@---------------------------------------------------------------------------------
ClearMem:
@---------------------------------------------------------------------------------
mov r2,#3 @ These commands are used in cases where
add r1,r2 @ the length is not a multiple of 4,
bic r1,r2 @ even though it should be.
beq ClearMX @ Length is zero so exit
mov r2,#0
@---------------------------------------------------------------------------------
ClrLoop:
@---------------------------------------------------------------------------------
stmia r0!, {r2}
sub r1,#4
bne ClrLoop
@---------------------------------------------------------------------------------
ClearMX:
@---------------------------------------------------------------------------------
bx lr
@---------------------------------------------------------------------------------
_blx_r3_stub:
@---------------------------------------------------------------------------------
bx r3
@---------------------------------------------------------------------------------
@ Copy memory if length != 0
@---------------------------------------------------------------------------------
@ r1 = Source Address
@ r2 = Dest Address
@ r4 = Dest Address + Length
@---------------------------------------------------------------------------------
CopyMemChk:
@---------------------------------------------------------------------------------
sub r3, r4, r2 @ Is there any data to copy?
@---------------------------------------------------------------------------------
@ Copy memory
@---------------------------------------------------------------------------------
@ r1 = Source Address
@ r2 = Dest Address
@ r3 = Length
@---------------------------------------------------------------------------------
CopyMem:
@---------------------------------------------------------------------------------
mov r0, #3 @ These commands are used in cases where
add r3, r0 @ the length is not a multiple of 4,
bic r3, r0 @ even though it should be.
beq CIDExit @ Length is zero so exit
@---------------------------------------------------------------------------------
CIDLoop:
@---------------------------------------------------------------------------------
ldmia r1!, {r0}
stmia r2!, {r0}
sub r3, #4
bne CIDLoop
@---------------------------------------------------------------------------------
CIDExit:
@---------------------------------------------------------------------------------
bx lr
.align
.pool
.end