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@ Tiny bare metal example
@ vim:ft=armv5
.section .init
_start:
LDR PC, [PC, #24] @ Reset
LDR PC, [PC, #24] @ Undefined
LDR PC, [PC, #24] @ SWI
LDR PC, [PC, #24] @ Prefetch abort
LDR PC, [PC, #24] @ Data abort
LDR PC, [PC, #24] @ Reserved
LDR PC, [PC, #24] @ IRQ
LDR PC, [PC, #24] @ FIQ
.word reset @ Reset
.word hang @ Undefined
.word swi_handler @ SWI
.word hang @ Prefetch abort
.word hang @ Data abort
.word hang @ Reserved
.word hang @ IRQ
.word hang @ FIQ
hang:
B hang
reset:
@ Hang all except one of the processors
MRC P15, 0, R0, C0, C0, 5
AND R0, R0, #3
CMP R0, #0
BNE hang
@ Get out of HYP mode
MRS R0, CPSR
BIC R0, R0, #0x1f
ORR R0, R0, #0x13
MSR SPSR_cxsf, R0
ADD R0, PC, #4
MSR ELR_hyp,r0
ERET
LDR R13, =stack_svc @ Set up stack for SVC mode
@ Relocate vector table
MOV R10, #0x8000
MOV R11, #0
LDMIA R10!, {R0-R7}
STMIA R11!, {R0-R7}
LDMIA R10!, {R0-R7}
STMIA R11!, {R0-R7}
LDR R8, =0x3f200000
LDR R1, [R8, #0x04] @ GPFSEL1
ORR R1, R1, #1<<18 @ GPIO pin 16 is output
BIC R1, R1, #3<<21 @ GPIO pin 17 is input
ORR R1, R1, #1<<24 @ GPIO pin 18 is output
STR R1, [R8, #0x04] @ GPFSEL1
@ Flash green LED
MOV R1, #1<<18
STR R1, [R8, #0x1c] @ GPSET0
BL pause
MOV R1, #1<<18
STR R1, [R8, #0x28] @ GPCLR0
BL pause
@ Switch to USR mode and set up stack
MRS R0, CPSR
BIC R0, R0, #0x1f
ORR R0, R0, #0x10
MSR CPSR_c, R0
LDR R13, =stack_usr
repeat:
MOV R0, #0
SWI 0
TST R0, #1<<17
MOVNE R0, #1
SWINE 0
B repeat
swi_handler:
STMDB R13!, {R8, LR}
LDR R8, =0x3f200000
CMP R0, #0
BEQ get_gpio
CMP R0, #1
BLEQ flash
LDMIA R13!, {R8, PC}^
get_gpio:
LDR R0, [R8, #0x34] @ GPLEV0
LDMIA R13!, {R8, PC}^
flash:
STMDB R13!, {R1, R2, R4, LR}
MOV R4, #5
flashloop:
MOV R1, #1<<16
STR R1, [R8, #0x28] @ GPCLR0
MOV R1, #1<<18
STR R1, [R8, #0x1c] @ GPSET0
BL pause
MOV R1, #1<<18
STR R1, [R8, #0x28] @ GPCLR0
MOV R1, #1<<16
STR R1, [R8, #0x1c] @ GPSET0
BL pause
MOV R1, #1<<18
ORR R1, #1<<16
STR R1, [R8, #0x28] @ GPCLR0
SUBS R4, R4, #1
BNE flashloop
LDMIA R13!, {R1, R2, R4, PC}
pause:
MOV R2, #0x3f000
wait:
SUBS R2, R2, #1
BNE wait
MOV PC, LR
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