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SCHG:Sonic Jam 6/ROM Editing
From Sonic Retro
| SCHG: Sonic Jam 6 |
|---|
| Main Article |
| ROM Editing |
| Editing ROM |
| RAM Editing |
| Editing RAM |
| Art Editing |
| Editing Art |
| Value Reference |
| Value Reference |
Values
| Offset | Description | Note |
|---|---|---|
| 0x1430 | Array which contains music numbers for each map (WORD ARRAY). | |
| 0x0ad2 | Demo properties (structure array, 0xe bytes long). |
|
| 0x0dde | Level map world-level number (structure array, 0x4 bytes long). |
|
Functions
Title Screen Functions
Button check
| Offset | Description |
|---|---|
| ROM:00000B18 | title_screen_check_buttons CODE XREF: sub_84E+15C�p. |
| ROM:00000B18 | btst #5,(word_FF001C).l ; Check  button.
|
| ROM:00000B20 | bne.w loc_B4C ; If it's pressed, branch. |
| ROM:00000B24 | btst #7,(word_FF001C).l ; Check  button.
|
| ROM:00000B2C | bne.w loc_B4C ; If it's pressed, branch. |
| ROM:00000B30 | btst #6,(word_FF001C).l ; Check  button.
|
| ROM:00000B38 | bne.w loc_B4C ;If it's pressed, branch. |
| ROM:00000B3C | btst #4,(word_FF001C).l ; Check  button.
|
| ROM:00000B44 | bne.w loc_B4C ; If it's pressed, branch. |
| ROM:00000B48 | bra.w locret_B6A ; No button pressed, branch to this other one. |
Level Functions
Bonus Level
| Offset | Instruction | Comment |
|---|---|---|
| ROM:0000780A | move.w d3,d0 | |
| ROM:0000780C | mulu.w #$20,d0 | |
| ROM:00007810 | cmpi.w #0,4(a6,d0.w) | |
| ROM:00007816 | bne.w loc_792A | |
| ROM:0000781A | cmpi.w #2,(word_FF0042).l | Compare 2 with current level map number |
| ROM:00007822 | beq.w loc_7836 | If level map number is 2, branch |
| ROM:00007826 | cmpi.w #5,(word_FF0042).l | Compare 5 with current level map number |
| ROM:0000782E | beq.w loc_7836 | If level map number is 5, branch |
| ROM:00007832 | bra.w loc_7842 |
As you can clearly see, level map number 2 and 5 are respectively the Level 1-1 bonus, and the Level 1-2 bonus. This makes the level not restart after exiting out of this level and returning to the main one, making it appear as a single level. Adding another level to the list should be as simple as adding a cmp instruction and branching accordingly.
Sound Driver Functions
The first two routines described below are easy to use subroutines which can be used respectively to play a background music or a sound effect. They handle calling the sound driver for you.
The BGM one is used by loading a word containing a music number from 0x0000 to 0x00FF into the address $ff6c00, and by jumping to it with a jump or branch to subroutine.
The SFX one works the same as the BGM one, but a sfx number is loaded into address $ff6c02.
The first line of the functions is their starting address.
Play BGM
| Offset | Instruction | Comment |
|---|---|---|
| ROM:000EE76C | move.w d0,-(sp) | Save d0 onto stack |
| ROM:000EE76E | move.w #0,d0 | Move 0 into d0 |
| ROM:000EE772 | move.b (word_FF6C00+1).l,d0 | Move lower byte of word at ff6c00 into lower byte of d0 |
| ROM:000EE778 | move.w d0,(word_FF6D00).l | Move d0 into address $ff6d00 |
| ROM:000EE77E | jsr sound_driver_play | Go to sub_F004C subroutine |
| ROM:000EE784 | move.w (sp)+,d0 | Load d0 from stack |
| ROM:000EE786 | rts | Return (from this Subroutine) |
Play SFX
| Offset | Instruction | Comment |
|---|---|---|
| ROM:000EE788 | move.w d0,-(sp) | Save d0 onto stack |
| ROM:000EE78A | move.w #$8000,d0 | Move $8000 into d0 |
| ROM:000EE78E | move.b (word_FF6C02+1).l,d0 | Move lower byte of word at $ff6c02 into lower byte of d0 |
| ROM:000EE794 | move.w d0,(word_FF6D00).l | Move d0 into word at address $ff6d00 (sound driver related) |
| ROM:000EE79A | jsr sound_driver_play | Jump to (sound driver play?) subroutine |
| ROM:000EE7A0 | move.w (sp)+,d0 | Load d0 from stack |
| ROM:000EE7A2 | rts | Return (from this Subroutine) |
