mini/start.S

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ArmAsm
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.arm
.extern _main
.extern __got_start
.extern __got_end
.extern __bss_start
.extern __bss_end
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.extern __bss2_start
.extern __bss2_end
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.extern __stack_addr
.globl _start
.globl debug_output
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.extern v_irq
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.section .init
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_vectors:
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_start:
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ldr pc, =v_reset
ldr pc, =v_undf
ldr pc, =v_swi
ldr pc, =v_instr_abrt
ldr pc, =v_data_abrt
ldr pc, =v_reserved
ldr pc, =v_irq
ldr pc, =v_fiq
.pool
v_reset:
@ Get loader base from ELF loader
mov r4, r0
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@ Output 0x42 to the debug port
mov r0, #0x42
bl debug_output
@ Set up a stack
ldr sp, =__stack_addr
add sp, r4
@ clear BSS
ldr r1, =__bss_start
add r1, r4
ldr r2, =__bss_end
add r2, r4
mov r3, #0
bss_loop:
@ check for the end
cmp r1, r2
beq done_bss
@ clear the word and move on
str r3, [r1]
add r1, r1, #4
b bss_loop
done_bss:
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@ clear BSS2
ldr r1, =__bss2_start
add r1, r4
ldr r2, =__bss2_end
add r2, r4
mov r3, #0
bss2_loop:
@ check for the end
cmp r1, r2
beq done_bss2
@ clear the word and move on
str r3, [r1]
add r1, r1, #4
b bss2_loop
done_bss2:
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mov r0, #0x84
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bl debug_output
@ take the plunge
mov r0, r4
bl _main
@ _main returned! Go to whatever address it returned...
mov pc, r0
.pool
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v_undf:
b v_undf
v_swi:
b v_swi
v_instr_abrt:
b v_instr_abrt
v_data_abrt:
b v_data_abrt
v_reserved:
b v_reserved
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#v_irq:
# b v_irq
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v_fiq:
b v_fiq
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debug_output:
@ load address of port
mov r3, #0xd800000
@ load old value
ldr r2, [r3, #0xe0]
@ clear debug byte
bic r2, r2, #0xFF0000
@ insert new value
and r0, r0, #0xFF
orr r2, r2, r0, LSL #16
@ store back
str r2, [r3, #0xe0]
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bx lr
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.pool