rsandor / decay

NES Music & Sound Engine

Decay NES Audio Engine

By Ryan Sandor Richards

Expected Memory Layout

The decay sound engine assumes the following memory layout:

+---------------+-----------------------------------------+-----------+
| Address       | Purpose                                 | Size      |
+---------------+-----------------------------------------+-----------+
| $00 - $0F     | Sub routine arguments                   | 256 bytes |
| $10 - $FF     | Temporary sub routine variables         |           |
+---------------+-----------------------------------------+-----------+
| $0100 - $01FF | Stack                                   | 256 bytes |
+---------------+-----------------------------------------+-----------+
| $0200 - $02FF | OAM (Sprite) Memory                     | 256 bytes |
+---------------+-----------------------------------------+-----------+
| $0300 - $03FF | Decay sound engine state                | 256 bytes |
+---------------+-----------------------------------------+-----------+
| $0400 - $07FF | Program Specific Variables              | 1 KB      |
+---------------+-----------------------------------------+-----------+

While your program does not have to follow this layout exactly it must reserve at least one page (256 bytes) of RAM for use by decay. You can change the page offset in the decay/header.s file.

lda #.LOBYTE(song_label)
sta $00
lda #.HIBYTE(song_label)
sta $01
jsr decay_load_song



DecayLoadSong song_label