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GGSound Guide

by Derek Andrews [email protected]

Introduction:

GGSound is a lightweight sound engine for use in NES homebrew games. It comes with an easy to use python script called ft_txt_to_asm.py which converts FamiTracker text exports into data usable by this sound engine. It supports a subset of FamiTracker's features, so that the amount of cpu time required by GGSound while in use in a game is smaller than the full FamiTracker driver. The trade-off is that a composer working with this sound engine will have to bake effects into individual envelopes, in most cases.

This guide explains how to use GGSound and its associated tools. The GGSound distribution comes with the following:

• /ggsound_ca65: This demo shows how to use ggsound with ca65. It requires that you have python 3 and cc65 installed in order to build it. Simply run build.py to build the demo and clean.py to clean it.

• /ggsound_asm6: This demo shows how to use ggsound with asm6. It requires that you have asm6 installed in order to build it. Simply run build.bat to build it and clean.bat to clean it.

• /ggsound_nesasm: This demo shows how to use ggsound with nesasm3. It requires that you have nesasm3 installed in order to build it. Simply run build.bat to build it and clean.bat to clean it.

• demo.nes: A prebuilt NES rom so you can quickly check out what GGSound can do in your favorite emulator.

• README.md: You're reading it.

• LICENSE: A file stating that GGSound is public domain and you may do anything you like with it. I'd appreciate credit, but other than that courtesy I do not require you do anything else, and feel free to sell anything you make using it.

Features:

GGSound is intended to be an easy to use and lightweight sound engine. It is able to create most of the sounds one would have heard in professional NES games from the 80's and 90's. It currently supports:

• Square 1, 2, Triangle, Noise, and DPCM channels
• Volume, Arpeggio, Pitch and Duty envelopes
• All three arpeggio types are supported.
• Hi-Pitch envelopes are NOT supported
• Looping envelopes at an arbitrary loop point
• Speed and Tempo
• Looping with the Bxx (must be present in all channels, using unique patterns) command
• Note cuts
• Tempo and pitch adjustment for NTSC, PAL and Dendy
• Multi-song export
• Sound effects on two channels
• Pause/unpause
• Full 96 note range of FamiTracker
• 128 instruments
• 128 songs
• 128 sound effects

Credits:

• MotZilla - For testing a very early version of the engine.
• zxdplay - For using GGSound in his excellent game, StarKeeper.
• jsr - For enabling me to work with the FamiTracker code and learn from it.
• Shiru - For making FamiTone2 and inspiring me to improve GGSound.
• MetalSlime - For the Nerdy Nights sound tutorials.
• Joe Granato - For helping test the new and improved version of GGSound.
• Memblers - For including GGSound in his benchmark thread.
• Tepples - For tips and wisdom on nesdev.
• Rainwarrior - For tips and wisdom on nesdev.
• ggf1979 - For asking for new features on nesdev.
• alekmaul - For asking for new features on nesdev.
• Hamtaro126 - For asking for new features on nesdev.
• 8bitMicroGuy - For supplying a sample song to help exercise GGSound and the converter.
• Velathnos 2.0 - For supplying a sample song to help exercise GGSound and the converter.
• darryl.revok - For bug reports and supplying sample songs to help exercise GGSound and the converter.
• Peter McQuillan - For bug reports and supplying sample songs to help exercise GGSound and the converter.
• Famicuber - For bug reports and supplying sample songs to exercise GGSound.
• Kasumi - For kicking my butt and making me want to improve GGSound's performance (compact instruments feature) as well as bug reports.

Changes:

• 6-6-18: Fixed label sanitization bug, we were not sanitizing instrument names! Also now capital letters will show up in the asm.
• 2-2-18: Refactored how envelopes are stored and read during execution into a "compact instrument" 256 byte format. This helps performance but introduces the limitation that you cannot have extremely long volume, pitch or other envelopes togehter in one instrument, but should still be useful for most common use cases. You can work around this limitation with additional instruments in the rare case you need many long envelopes end to end.
• 1-25-18: Refactored arpeggio execution to support all three arpeggio types: absolute, fixed and relative. Re-tested with FamiCuber's track. This is a new feature, please send me bug reports if you run into any problems. Added FamiTracker's full 96 note range table.
• 1-20-18: Fixed regression from noise arpeggio execution which would prevent noise pitch envelopes from executing. This bug included fixes in ft_txt_to_asm.py and in ggsound itself. Please re-convert your song data if you have run into this issue. Added Famicuber's drum loop to songs.ftm demonstrating noise arpeggios working alongside noise pitch envelopes (one of the sfx in the demo)
• 1-14-18: Fixed bug in arpeggio execution for square and triangle channels. Added arpeggio support for the noise channel.
• 6-4-17: Added pitch envelope support for the noise channel. Note that FamiTracker appears to stop at note 0 even if the delta continues down, but wraps after note 15 if the delta continues up. GGSound instead wraps regardless of whether the delta goes past 0 or 15.
• 8-28-16: Fixed two bugs in converter: Sfx envelope length determination has been fixed. Patterns are now looked up by id.
• 5-29-16: Fixed bug in converter so that all envelopes revert to default for instruments that do not specify them. Fixed how beginning of note is detected. Fixed arpeggio processing to work with new beginning of note code. Fixed bug in converter which was processing spaces in track and dpcm names incorrectly. Convert spaces to underscores in output asm for readability.
• 5-7-16: Implemented duty/noise envelopes for the noise channel. Better late than never!
• 5-4-16: Implemented duty cycle loop points for square waves. Added unlicense.txt to comfort people actually worried about legal issues with NES sound engines :)
• 5-2-16: Fixed regression from label name sanitization fixup. Gotta get rid of those quotes!
• 5-1-16: Fixed regression from fix for Bxx loop processing. Also added even more paranoia for label name sanitization. It's a jungle out there.
• 4-27-16: Fixed dpcm sample indexing. Added extra paranoia to label name sanitization.
• 4-23-16: Added track and dpcm label name sanitization. Fixed a bug in Bxx loop processing.
• 3-20-16: Added support for DPCM, arpeggios, Bxx, and pause.
• 2-17-16: Added support for note cuts.
• 1-16-16: Fixed a bug in ft_txt_to_asm.py for all assemblers that allows it to output correct song headers under Python 2.x.

Including GGSound in a CA65 program:

• ggsound.inc is needed for access to the ggsound api (usage guide later in this file).

• ggsound.asm may be compiled as its own object file. It requires that your configuration file have a ZEROPAGE, a BSS and a CODE segment defined in order to link successfully with your program.

Including GGSound in an ASM6 program:

• ggsound.inc: Include this at the top of your program. All ggsound data and usage of its routines will need these equates and macros.

• ggsound.asm: Include this in a PRG-ROM bank which has enough space.

• ggsound_zp.inc: Include this file within your zeropage enumeration, like this:

.base $0000
.enum $0000

include "demo_zp.inc"
include "ggsound_zp.inc"

.ende

• ggsound_ram.inc: Include this file within your BSS enumeration, like this:

.base $0200
.enum $0200

include "ggsound_ram.inc"

.ende

Including GGSound in a NESASM3 program:

• ggsound.inc: Include this at the top of your program. All ggsound data and usage of its routines will need these equates and macros.

• ggsound.asm: Include this in an 8kb nesasm3 bank which has enough space.

• ggsound_zp.inc: Include this file within your zeropage section, like this:

  .rsset $0000
  include "ggsound_zp.inc"

• ggsound_ram.inc: Include this file within your BSS section, like this:

  .rsset $0200
  include "ggsound_ram.inc"

Usage of ft_txt_to_asm.py

You must use ft_txt_to_asm.py to convert FamiTracker text output data into assembly language code for ggsound to use within your program. To use ft_txt_to_asm.py you will need to install Python 3.x. Go to www.python.org, click on Downloads, and then download Python 3.x for Windows. Run the installer and choose all defaults. This should be fairly self-explanatory. Note: The script may work under Python 2.x in most cases, but it has not been extensively tested. Please email me if you find bugs.

There are three versions of ft_txt_to_asm.py tailored for ca65, nesasm3 and asm6. You must use the one included with the demo for your target assembler, or the output will not work with your code.

To use it, follow these steps:

1. Open your .ftm file in FamiTracker.
2. Run Edit -> Clean Up -> Remove Unused Instruments.
3. Select File...Export Text.
4. Save the text file in a desired location, probably wherever your program files are.
5. Drag the text file to ft_txt_to_asm.py. If there are no errors, it will generate a file with the same name as the text file, but with .asm as the extension. It should place the asm file in the same folder that the txt file was. If you have any DPCM samples, a file with the same name _dpcm.asm will be generated.

If no asm file is generated, there may be an error. Run ft_txt_to_asm.py instead from a command line. You can run it like this:

python ft_txt_to_asm.py your_file.txt

Then, you can examine the error output. Please email me if you end up in this situation---you have either encountered a bug or a limitation in ft_txt_to_asm.py. Known limitations are documented below.

Limitations of ft_txt_to_asm.py

ft_txt_to_asm.py does not convert your famitracker data verbatim. It uses a subset of all the possible features you can use within a song. Here are a list of all the famitracker features and settings that are currently supported:

• Track speed
• Track tempo
• Pattern length
• Frames
• Multi-song files
• "Bxx" effect. This is for looping a song which does not end at the end of a frame. MAKE SURE TO INCLUDE THIS EFFECT AT THE END OF EACH OF YOUR SONG'S CHANNELS OR THE DATA WILL NOT BE CORRECT. THESE MUST BE IN UNIQUE PATTERNS.
• Note cuts
• Volume envelopes
• Arpeggio envelopes. These can be disabled if you do not wish to use them by setting ARPEGGIOS_ENABLED = False within ft_txt_to_asm.py, at the top of the file. Just open it in a text editor.
• All three arpeggio types.
• Pitch envelopes
• Hi-pitch envelopes are NOT supported
• Duty envelopes
• Loop point within envelopes
• Note that when ft_txt_to_asm.py converts your famitracker text file into assembly language, each instrument's constituent envelopes will be combined into a compact 256 byte structure. This means if you have any extremely long envelopes that will not fit together inside of 256 bytes, you will not be able to convert your song and the script will show you an error. In practice it is rare to have envelopes this long. To work around this limitation, you can create additional instruments whose envelopes pick up where the previous one left off, but this size should work for most purposes.
• All 96 notes within FamiTracker are available for you to use, though pitch will not change below A0, just as in FamiTracker itself.
• DPCM samples. The script assumes only one instrument has DPCM samples mapped to it. If you have more than one instrument which maps DPCM samples to notes, the behavior will be undefined. NOTE: Your DPCM instrument must specify a volume envelope, even though it is not used by DPCM. Otherwise, your DPCM stream will not be exported.
• Sound effect tracks. To export sound effect tracks, you must prefix any song within your famitracker file with "sfx_." This lets ft_txt_to_asm.py know to treat this track as a sound effect and make sure that it terminates after its longest envelope finishes.

Including your song data in your code in CA65

ft_txt_to_asm.py generates an .asm file you need to include in your code. For ca65, it is recommended to include this file in another file which wraps it in a segment that you desire to place your song data in. You will also need to expose your song_list, sfx_list, and envelopes_list symbols in order to be able to initialize ggsound properly. See tracks.asm and tracks.inc in the ggsound demo for an example. track_data.inc is a renamed version of the data generated by ft_txt_to_asm.py.

If you are using DPCM, a second file with the same name as your ft txt file will be generated with the suffix _dpcm.asm. This is your dpcm sample data. It is pre-aligned to 64 byte boundaries, but assumes you will place the data at a 64 byte aligned boundary to begin with. Note that your DPCM data MUST be at $C000 or later or it will not work.

Including your song data in asm6 or nesasm3

ft_txt_to_asm.py generates an .asm file you need to include in your code. To include your song .asm file in asm6 or nesasm3, this is much simpler. Just

include "songs.asm"

In a bank that has enough space. songs.asm will need to see the equates defined in ggsound.inc, so make sure ggsound.inc is somewhere above songs.asm.

If you are using DPCM, a second file with the same name as your ft txt file will be generated with the suffix _dpcm.asm. This is your dpcm sample data. It is pre-aligned to 64 byte boundaries, but assumes you will place the data at a 64 byte aligned boundary to begin with. ASM6 allows you to use .ALIGN 64 to do this. In nesasm3, your best bet would be to include your dpcm data at the very beginning of a dedicated bank. Note that your DPCM data MUST be at $C000 or later or it will not work.

Basic usage of GGSound

Initialization:

To initialize GGSound, you must call sound_initialize. You need to tell it which region to use (NTSC, PAL, or Dendy), and the addresses of lists of songs, sound effects, envelopes and dpcm samples. These lists are located at the top of the asm file that you generate from your songs file with ft_txt_to_asm.py.

    lda #SOUND_REGION_NTSC ;or #SOUND_REGION_PAL, or #SOUND_REGION_DENDY
    sta sound_param_byte_0
    lda #<song_list
    sta sound_param_word_0
    lda #>song_list
    sta sound_param_word_0+1
    lda #<sfx_list
    sta sound_param_word_1
    lda #>sfx_list
    sta sound_param_word_1+1
    lda #<envelopes_list
    sta sound_param_word_2
    lda #>envelopes_list
    sta sound_param_word_2+1
    lda #<dpcm_list
    sta sound_param_word_3
    lda #>dpcm_list
    sta sound_param_word_3+1
    jsr sound_initialize

Please note that if you disable DPCM, the dpcm_list label will not be available and you can just leave out the following lines:

    lda #<dpcm_list
    sta sound_param_word_3
    lda #>dpcm_list
    sta sound_param_word_3+1

If you are experimenting with the demo program, these lines are located in demo.asm.

Updating:

To hear anything at all, you must update GGSound on every frame. It is highly recommended that you use the provided "sound_update" macro at the end of your vblank routine to do this, like so:

vblank:
    pha
    txa
    pha
    tya
    pha
    php

    soundengine_update

    plp
    pla
    tay
    pla
    tax
    pla

irq:
    rti

Playing songs:

At the top of your songs.asm file above the song_list and sfx_list are some enumerated equates for each song and sound effect that you've included in your famitracker file. To play one, just load up one of these equates and call play_song, like this:

    lda #song_index_k466
    sta sound_param_byte_0
    jsr play_song

Please note that ft_txt_to_asm.py does not output any information about how many songs there are in your file, it is up to you to keep track of this. If you paste new data in track_data.inc in any of the demo programs, you will also have to modify demo.asm so that it won't play garbage songs past the end of your songs (it is hard coded for 6 songs as in the original demo data).

Playing sound effects:

Playing sound effects is nearly identical, except you must also specify the sound effect priority in a second parameter. This priority can be one of two values: soundeffect_one and soundeffect_two, defined in ggsound.inc. soundeffect_two, if played on the same channel, will override what soundeffect_one is playing.

    lda #sfx_index_sfx_shot
    sta sound_param_byte_0
    lda #soundeffect_one
    sta sound_param_byte_1
    jsr play_sfx

Please note that ft_txt_to_asm.py does not output any information about how many sfx there are in your file, it is up to you to keep track of this. If you paste new data in track_data.inc in any of the demo programs, you will also have to modify demo.asm to use constants that point to the indices of the two sfx you wish to demo.

Disabling features:

DPCM and arpeggio support can be disabled. To disable DPCM, comment out FEATURE_DPCM = 1 at the top of ggsound.inc. To disable arpeggios, comment out FEATURE_ARPEGGIOS = 1 at the top of ggsound.inc.

To disable DPCM from ft_txt_to_asm.py, just don't use any dpcm in your song and no dpcm streams will be exported. To disable arpeggios in ft_txt_to_asm.py is required if you are disabling it in ggsound itself. Change ARPEGGIOS_ENABLED to False within ft_txt_to_asm.py to avoid exporting any arpeggio data or opcodes.