megadrive_test2

annotate src/startup.s @ 4:72ab63f262bf

tiles
author John Tsiombikas <nuclear@member.fsf.org>
date Mon, 19 Jun 2017 08:02:51 +0300
parents b22bc95f0cc0
children 54caa2b214ca
rev   line source
nuclear@4 1 | vi:filetype=gas68k:
nuclear@0 2 .text
nuclear@0 3 .extern main
nuclear@0 4
nuclear@0 5 .global start
nuclear@0 6 .global halt_cpu
nuclear@0 7 start:
nuclear@1 8 jsr disable_intr
nuclear@0 9
nuclear@0 10 | copy .data section from ROM to RAM
nuclear@0 11 move.l #_data_lma, %a0
nuclear@0 12 move.l #_data_start, %a1
nuclear@0 13 move.l #_data_end, %a2
nuclear@0 14 cmp.l %a1, %a2
nuclear@0 15 beq.s 1f | skip data copy if the section is empty
nuclear@0 16 0: move.l (%a0)+, (%a1)+
nuclear@0 17 cmp.l %a1, %a2
nuclear@0 18 bne.s 0b
nuclear@0 19 1:
nuclear@0 20
nuclear@0 21 | zero the .bss section
nuclear@0 22 move.l #_bss_start, %a0
nuclear@0 23 move.l #_bss_end, %a1
nuclear@0 24 cmp.l %a0, %a1
nuclear@0 25 beq.s 1f | skip bss zeroing if the section is empty
nuclear@0 26 0: clr.l (%a0)+
nuclear@0 27 cmp.l %a0, %a1
nuclear@0 28 bne.s 0b
nuclear@0 29 1:
nuclear@0 30
nuclear@0 31 | setup the stack pointer stack
nuclear@0 32 move.l #_stacktop, %sp
nuclear@0 33 | now that we have a stack, we can enable interrupts
nuclear@1 34 jsr enable_intr
nuclear@0 35
nuclear@0 36 jsr main
nuclear@0 37 halt_cpu:
nuclear@0 38 stop #0x2700