megadrive_test1
annotate src/startup.s @ 7:8253942b0a1a
in the middle of something
| author | John Tsiombikas <nuclear@member.fsf.org> |
|---|---|
| date | Sun, 19 Feb 2017 14:00:26 +0200 |
| parents | 862f8a034cae |
| children |
| rev | line source |
|---|---|
| nuclear@0 | 1 .text |
| nuclear@0 | 2 .extern main |
| nuclear@0 | 3 |
| nuclear@0 | 4 .global start |
| nuclear@6 | 5 .global halt_cpu |
| nuclear@0 | 6 start: |
| nuclear@7 | 7 | copy the string 'SEGA' to appease the TMSS |
| nuclear@7 | 8 move.l 100, 0xa14000 | SEGA is always at address 100 |
| nuclear@7 | 9 |
| nuclear@3 | 10 | copy .data section from ROM to RAM |
| nuclear@3 | 11 move.l #_data_lma, %a0 |
| nuclear@3 | 12 move.l #_data_start, %a1 |
| nuclear@3 | 13 move.l #_data_end, %a2 |
| nuclear@3 | 14 cmp.l %a1, %a2 |
| nuclear@3 | 15 beq.s 1f | skip data copy if the section is empty |
| nuclear@3 | 16 0: move.l (%a0)+, (%a1)+ |
| nuclear@3 | 17 cmp.l %a1, %a2 |
| nuclear@3 | 18 bne.s 0b |
| nuclear@3 | 19 1: |
| nuclear@3 | 20 |
| nuclear@3 | 21 | zero the .bss section |
| nuclear@3 | 22 move.l #_bss_start, %a0 |
| nuclear@3 | 23 move.l #_bss_end, %a1 |
| nuclear@3 | 24 cmp.l %a0, %a1 |
| nuclear@3 | 25 beq.s 1f | skip bss zeroing if the section is empty |
| nuclear@3 | 26 0: clr.l (%a0)+ |
| nuclear@3 | 27 cmp.l %a0, %a1 |
| nuclear@3 | 28 bne.s 0b |
| nuclear@3 | 29 1: |
| nuclear@7 | 30 |
| nuclear@7 | 31 | setup the stack pointer stack |
| nuclear@7 | 32 move.l #_stacktop, %sp |
| nuclear@7 | 33 |
| nuclear@0 | 34 jsr main |
| nuclear@6 | 35 halt_cpu: |
| nuclear@0 | 36 stop #0x2700 |