mirror of
https://github.com/autc04/Retro68.git
synced 2024-11-30 19:53:46 +00:00
64 lines
1.5 KiB
ArmAsm
64 lines
1.5 KiB
ArmAsm
|
.text
|
||
|
|
.global _start
|
||
|
|
.type _start,@function
|
||
|
|
.stabs "crt0.S",100,0,0,_start
|
||
|
|
.stabs "int:t(0,1)=r(0,1);-32768;32767;",128,0,0,0
|
||
|
|
.stabs "_start:F(0,1)",36,0,1,_start
|
||
|
|
|
||
|
|
_start:
|
||
|
|
|
||
|
|
; R14 always contains memory base address (0)
|
||
|
|
|
||
|
|
ldi r14,0
|
||
|
|
|
||
|
|
; Set the USER and SYSTEM stack pointers.
|
||
|
|
|
||
|
|
ldi r0, 0 ; zero arguments
|
||
|
|
ldi r1, 0
|
||
|
|
mvtc r0, psw ; select SPI and set it
|
||
|
|
ldi sp, _stack
|
||
|
|
ldi r10, 0x8000 ; select SPU/FP and set it
|
||
|
|
mvtc r10, psw || ldi r11, 0; clear stack frame
|
||
|
|
ldi sp, _stack - 0x200
|
||
|
|
ldi r13, 0
|
||
|
|
|
||
|
|
; Clear the BSS. Do it in two parts for efficiency: longwords first
|
||
|
|
; for most of it, then the remaining 0 to 3 bytes.
|
||
|
|
|
||
|
|
ldi r2, __bss_start ; R2 = start of BSS
|
||
|
|
ldi r3, _end ; R3 = end of BSS + 1
|
||
|
|
sub r3, r2 ; R3 = BSS size in bytes
|
||
|
|
mv r4, r3
|
||
|
|
srli r4, 2 ; R4 = BSS size in longwords (rounded down)
|
||
|
|
loop1:
|
||
|
|
cmpeqi r4, 0 ; more longords to zero out?
|
||
|
|
brf0t.s endloop1 ; nope
|
||
|
|
st2w r0, @r2+ ; yep, zero out another longword
|
||
|
|
subi r4, 1 ; decrement count
|
||
|
|
bra.l loop1 ; go do some more
|
||
|
|
|
||
|
|
endloop1:
|
||
|
|
and3 r4, r3, 3 ; get no. of remaining BSS bytes to clear
|
||
|
|
loop2:
|
||
|
|
cmpeqi r4, 0 ; more bytes to zero out?
|
||
|
|
brf0t.s endloop2 ; nope
|
||
|
|
stb r0, @r2 ; yep, zero out another byte
|
||
|
|
addi r2, 1 ; bump address
|
||
|
|
subi r4, 1 ; decrement count
|
||
|
|
bra.s loop2 ; go do some more
|
||
|
|
endloop2:
|
||
|
|
; Call main, then stop simulator
|
||
|
|
st r11, @-sp
|
||
|
|
st r13, @-sp
|
||
|
|
mv r11, sp
|
||
|
|
|
||
|
|
bl main
|
||
|
|
bl exit
|
||
|
|
stop
|
||
|
|
.Lstart:
|
||
|
|
.size _start,.Lstart-_start
|
||
|
|
.stabs "",36,0,0,.Lstart-_start
|
||
|
|
|
||
|
|
.section .stack
|
||
|
|
_stack: .long 1
|