megadrive_test2
view src/startup.s @ 0:ce1b05082ac4
initial commit
| author | John Tsiombikas <nuclear@member.fsf.org> |
|---|---|
| date | Tue, 14 Mar 2017 05:59:33 +0200 |
| parents | |
| children | 2560a8be8cb8 |
line source
1 .text
2 .extern main
4 .global start
5 .global halt_cpu
6 start:
7 bsr.s disable_intr
9 | copy .data section from ROM to RAM
10 move.l #_data_lma, %a0
11 move.l #_data_start, %a1
12 move.l #_data_end, %a2
13 cmp.l %a1, %a2
14 beq.s 1f | skip data copy if the section is empty
15 0: move.l (%a0)+, (%a1)+
16 cmp.l %a1, %a2
17 bne.s 0b
18 1:
20 | zero the .bss section
21 move.l #_bss_start, %a0
22 move.l #_bss_end, %a1
23 cmp.l %a0, %a1
24 beq.s 1f | skip bss zeroing if the section is empty
25 0: clr.l (%a0)+
26 cmp.l %a0, %a1
27 bne.s 0b
28 1:
30 | setup the stack pointer stack
31 move.l #_stacktop, %sp
32 | now that we have a stack, we can enable interrupts
33 bsr.s enable_intr
35 jsr main
36 halt_cpu:
37 stop #0x2700
39 .global enable_intr
40 enable_intr:
41 andi.w #0xf8ff, %sr
42 rts
44 .global disable_intr
45 disable_intr:
46 ori.w #0x0300, %sr
47 rts