megadrive_test2

view src/startup.s @ 9:6ecf2f3ff05a

find changesets by author, revision, files, or words in the commit message
- better pad input handling - switch between 28 and 30 vertical tiles by pressing C
author John Tsiombikas <nuclear@member.fsf.org>
date Sat, 24 Jun 2017 00:33:10 +0300
parents b22bc95f0cc0
children 54caa2b214ca
line source
1 | vi:filetype=gas68k:
2 .text
3 .extern main
4
5 .global start
6 .global halt_cpu
7 start:
8 jsr disable_intr
9
10 | copy .data section from ROM to RAM
11 move.l #_data_lma, %a0
12 move.l #_data_start, %a1
13 move.l #_data_end, %a2
14 cmp.l %a1, %a2
15 beq.s 1f | skip data copy if the section is empty
16 0: move.l (%a0)+, (%a1)+
17 cmp.l %a1, %a2
18 bne.s 0b
19 1:
20
21 | zero the .bss section
22 move.l #_bss_start, %a0
23 move.l #_bss_end, %a1
24 cmp.l %a0, %a1
25 beq.s 1f | skip bss zeroing if the section is empty
26 0: clr.l (%a0)+
27 cmp.l %a0, %a1
28 bne.s 0b
29 1:
30
31 | setup the stack pointer stack
32 move.l #_stacktop, %sp
33 | now that we have a stack, we can enable interrupts
34 jsr enable_intr
35
36 jsr main
37 halt_cpu:
38 stop #0x2700