261 lines
9.6 KiB
ArmAsm
261 lines
9.6 KiB
ArmAsm
/*--------------------------------------------------------------------------------
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Copyright devkitPro Project
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https://github.com/devkitPro/devkitarm-crtls/blob/master/gba_crt0.s
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This Source Code Form is subject to the terms of the Mozilla Public License,
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v. 2.0. If a copy of the MPL was not distributed with this file, You can
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obtain one at https://mozilla.org/MPL/2.0/.
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--------------------------------------------------------------------------------*/
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.section ".crt0","ax"
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.global _start
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.align
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.arm
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.cpu arm7tdmi
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@---------------------------------------------------------------------------------
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_start:
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@---------------------------------------------------------------------------------
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b rom_header_end
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.fill 156,1,0 @ Nintendo Logo Character Data (8000004h)
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.fill 16,1,0 @ Game Title
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.byte 0x30,0x31 @ Maker Code (80000B0h)
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.byte 0x96 @ Fixed Value (80000B2h)
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.byte 0x00 @ Main Unit Code (80000B3h)
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.byte 0x00 @ Device Type (80000B4h)
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.fill 7,1,0 @ unused
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.byte 0x00 @ Software Version No (80000BCh)
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.byte 0xf0 @ Complement Check (80000BDh)
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.byte 0x00,0x00 @ Checksum (80000BEh)
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@---------------------------------------------------------------------------------
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rom_header_end:
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@---------------------------------------------------------------------------------
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b start_vector @ This branch must be here for proper
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@ positioning of the following header.
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.GLOBAL __boot_method, __slave_number
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@---------------------------------------------------------------------------------
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__boot_method:
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@---------------------------------------------------------------------------------
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.byte 0 @ boot method (0=ROM boot, 3=Multiplay boot)
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@---------------------------------------------------------------------------------
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__slave_number:
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@---------------------------------------------------------------------------------
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.byte 0 @ slave # (1=slave#1, 2=slave#2, 3=slave#3)
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.byte 0 @ reserved
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.byte 0 @ reserved
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.word 0 @ reserved
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.word 0 @ reserved
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.word 0 @ reserved
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.word 0 @ reserved
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.word 0 @ reserved
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.word 0 @ reserved
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.global start_vector
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.align
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@---------------------------------------------------------------------------------
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start_vector:
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@---------------------------------------------------------------------------------
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mov r0, #0x4000000 @ REG_BASE
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str r0, [r0, #0x208]
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mov r0, #0x12 @ Switch to IRQ Mode
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msr cpsr, r0
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ldr sp, =__sp_irq @ Set IRQ stack
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mov r0, #0x1f @ Switch to System Mode
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msr cpsr, r0
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ldr sp, =__sp_usr @ Set user stack
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@---------------------------------------------------------------------------------
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@ Enter Thumb mode
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@---------------------------------------------------------------------------------
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add r0, pc, #1
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bx r0
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.thumb
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ldr r0, =__text_start
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lsl r0, #5 @ Was code compiled at 0x08000000 or higher?
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bcs DoEWRAMClear @ yes, you can not run it in external WRAM
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mov r0, pc
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lsl r0, #5 @ Are we running from ROM (0x8000000 or higher) ?
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bcc SkipEWRAMClear @ No, so no need to do a copy.
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@---------------------------------------------------------------------------------
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@ We were started in ROM, silly emulators. :P
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@ So we need to copy to ExWRAM.
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@---------------------------------------------------------------------------------
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mov r2, #2
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lsl r2, r2, #24 @ r2= 0x02000000
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ldr r3, =__end__ @ last ewram address
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sub r3, r2 @ r3= actual binary size
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mov r6, r2 @ r6= 0x02000000
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lsl r1, r2, #2 @ r1= 0x08000000
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bl CopyMem
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bx r6 @ Jump to the code to execute
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@---------------------------------------------------------------------------------
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DoEWRAMClear: @ Clear External WRAM to 0x00
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@---------------------------------------------------------------------------------
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mov r1, #0x40
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lsl r1, #12 @ r1 = 0x40000
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lsl r0, r1, #7 @ r0 = 0x2000000
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bl ClearMem
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@---------------------------------------------------------------------------------
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SkipEWRAMClear: @ Clear Internal WRAM to 0x00
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@---------------------------------------------------------------------------------
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@---------------------------------------------------------------------------------
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@ Clear BSS section to 0x00
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@---------------------------------------------------------------------------------
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ldr r0, =__bss_start__
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ldr r1, =__bss_end__
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sub r1, r0
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bl ClearMem
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@---------------------------------------------------------------------------------
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@ Clear SBSS section to 0x00
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@---------------------------------------------------------------------------------
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ldr r0, =__sbss_start__
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ldr r1, =__sbss_end__
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sub r1, r0
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bl ClearMem
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@---------------------------------------------------------------------------------
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@ Copy initialized data (data section) from LMA to VMA (ROM to RAM)
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@---------------------------------------------------------------------------------
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ldr r1, =__data_lma
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ldr r2, =__data_start__
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ldr r4, =__data_end__
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bl CopyMemChk
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@---------------------------------------------------------------------------------
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@ Copy internal work ram (iwram section) from LMA to VMA (ROM to RAM)
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@---------------------------------------------------------------------------------
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ldr r1,= __iwram_lma
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ldr r2,= __iwram_start__
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ldr r4,= __iwram_end__
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bl CopyMemChk
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@---------------------------------------------------------------------------------
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@ Copy internal work ram overlay 0 (iwram0 section) from LMA to VMA (ROM to RAM)
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@---------------------------------------------------------------------------------
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ldr r2,= __load_stop_iwram0
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ldr r1,= __load_start_iwram0
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sub r3, r2, r1 @ Is there any data to copy?
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beq CIW0Skip @ no
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ldr r2,= __iwram_overlay_start
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bl CopyMem
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@---------------------------------------------------------------------------------
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CIW0Skip:
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@---------------------------------------------------------------------------------
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@ Copy external work ram (ewram section) from LMA to VMA (ROM to RAM)
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@---------------------------------------------------------------------------------
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ldr r1, =__ewram_lma
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ldr r2, =__ewram_start
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ldr r4, =__ewram_end
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bl CopyMemChk
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@---------------------------------------------------------------------------------
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CEW0Skip:
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@---------------------------------------------------------------------------------
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@ set heap end
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@---------------------------------------------------------------------------------
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// fake_heap_end does not appear to exist,
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// and Nostalgia has its own heap allocator anyway
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//ldr r1, =fake_heap_end
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//ldr r0, =__eheap_end
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//str r0, [r1]
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@---------------------------------------------------------------------------------
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@ global constructors
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@---------------------------------------------------------------------------------
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ldr r3, =__libc_init_array
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bl _blx_r3_stub
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@---------------------------------------------------------------------------------
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@ Jump to user code
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@---------------------------------------------------------------------------------
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mov r0, #0 @ int argc
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mov r1, #0 @ char *argv[]
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ldr r3, =main
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bl _blx_r3_stub
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@---------------------------------------------------------------------------------
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@ Clear memory to 0x00 if length != 0
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@---------------------------------------------------------------------------------
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@ r0 = Start Address
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@ r1 = Length
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@---------------------------------------------------------------------------------
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ClearMem:
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@---------------------------------------------------------------------------------
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mov r2,#3 @ These commands are used in cases where
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add r1,r2 @ the length is not a multiple of 4,
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bic r1,r2 @ even though it should be.
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beq ClearMX @ Length is zero so exit
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mov r2,#0
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@---------------------------------------------------------------------------------
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ClrLoop:
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@---------------------------------------------------------------------------------
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stmia r0!, {r2}
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sub r1,#4
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bne ClrLoop
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@---------------------------------------------------------------------------------
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ClearMX:
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@---------------------------------------------------------------------------------
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bx lr
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@---------------------------------------------------------------------------------
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_blx_r3_stub:
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@---------------------------------------------------------------------------------
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bx r3
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@---------------------------------------------------------------------------------
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@ Copy memory if length != 0
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@---------------------------------------------------------------------------------
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@ r1 = Source Address
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@ r2 = Dest Address
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@ r4 = Dest Address + Length
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@---------------------------------------------------------------------------------
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CopyMemChk:
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@---------------------------------------------------------------------------------
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sub r3, r4, r2 @ Is there any data to copy?
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@---------------------------------------------------------------------------------
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@ Copy memory
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@---------------------------------------------------------------------------------
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@ r1 = Source Address
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@ r2 = Dest Address
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@ r3 = Length
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@---------------------------------------------------------------------------------
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CopyMem:
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@---------------------------------------------------------------------------------
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mov r0, #3 @ These commands are used in cases where
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add r3, r0 @ the length is not a multiple of 4,
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bic r3, r0 @ even though it should be.
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beq CIDExit @ Length is zero so exit
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@---------------------------------------------------------------------------------
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CIDLoop:
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@---------------------------------------------------------------------------------
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ldmia r1!, {r0}
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stmia r2!, {r0}
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sub r3, #4
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bne CIDLoop
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@---------------------------------------------------------------------------------
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CIDExit:
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@---------------------------------------------------------------------------------
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bx lr
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.align
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.pool
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.end
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