Using GoatTracker to Create F256K SID Music

This guide explains how to use GoatTracker to compose SID music and generate a packed .bin file that plays correctly on the F256K / F256K2 FPGA SID.

This document focuses on SID-only usage (no PSG or other sound chips).

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1. Getting GoatTracker

GoatTracker is available for Windows, macOS, and Linux.
Download page: https://cadaver.github.io/
The stereo version (useful for dual SIDs on F256K2) is available on SourceForge under the files tab.

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2. Creating a Song

Create and edit your song in GoatTracker as you would for a C64.
Most instruments, effects, and patterns work correctly on the F256K FPGA SID.
GoatTracker was tuned for real C64 hardware, so FPGA SIDs may sound slightly different.

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3. Pitch and Timing (Important)

Pitch and playback speed are related but separate settings.

Playback speed is controlled by PAL vs NTSC timing (50 Hz vs 60 Hz).
Pitch is controlled by the A-4 tuning value.

The F256K uses NTSC (60 Hz) timing so Goattracker must be configured accordingly.

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3.1 Editing and Previewing on Your Computer

When composing music on your computer, use NTSC timing and corrected pitch.

Recommended settings:

goattracker -N -G424 song.sng

-N — NTSC timing (60 Hz)
-G424 — Correct pitch for NTSC preview

This setting is for editing only.

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3.2 Packing for Playback on the F256K

The F256K requires a different tuning to produce true 440 Hz pitch.

Tested value:

A-4 = 454 Hz

When packing a song, always start GoatTracker with the correct tuning and the song loaded at startup:

goattracker -G454 song.sng

Important: .sng files store tuning. Loading after startup will overwrite the setting and result in an incorrectly tuned packed file.

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4. Packing the Song

Songs must be packed into a self-playing binary for use on the F256.

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Option A: Internal Pack (F9)

Press F9 in GoatTracker.
Ensure it was started with -G454 and the song loaded.

The internal packer always uses the current tuning.

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Option B: External Packer (GT2RELOC.EXE)

Recommended method.

Example command:

GT2RELOC song.sng song.bin -N -G454 -LD400 -Wa0 -Z80

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Parameter Explanation

song.sng — Input song
song.bin — Output binary
-N — NTSC timing
-G454 — F256K tuning
-LD400 — SID base address
-Wa0 — Player load address ($A000)
-Z80 — Zeropage ($80/$81)

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Notes

-Wxx sets the high byte only
- Example:-Wa0 = $A000
-Zxx specifies the starting zeropage address
- uses two bytes
  - $80/$81 is tested and safe
  - Avoid $F0–$FF (kernel use)
-Wxx and -Zxx are configurable based on your program's memory layout.

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5. Playing the Music

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5.1 Initialization

Call the music player's init routine once. It is located at the player load address (-Wxx).

JSR $A000 ; initialize song

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5.2 Per-Frame Playback

Call the playback routine once per frame (SOF / 60 Hz).

Playback routine address = init + 3

JSR $A003 ; play song for this frame

Repeat this call every frame for continuous playback.

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6. Additional Notes

Pitch and speed are not the same:
- -N controls speed
- -Gxx controls pitch
GoatTracker adjusts pitch tables when switching PAL/NTSC, but manual A-4 correction is still required.
The packed .bin file is unchanged between the C64 and the F256 - compatibility comes from correct timing, tuning, and memory placement.

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Appendix: Minimal F256 SID Music Player Example

The following is a minimal working music player using kernel timers.

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This example matches the configuration described in this wiki page:

Player loaded at $A000 (-Wa0)
Player routine at $A003
Zeropage usage at $80/$81 (used internally by the player)
NTSC / 60 Hz playback

; ============================================================================
; music_min.asm - Minimal Music Player for Wildbits/K & /Jr
; ============================================================================

   .cpu "65816"
   MMU_IO_CTRL = $01
   init_music = $A000
   play_music = init_music+3
   timer_cookie = $D0

*=$A0
   .dsection zp
   .cerror * > $AF, "Too many zero page variables"

   .include "api.asm"

   .section zp
   event: .dstruct kernel.event.event_t
   .send

*=$1000

start:
   stz MMU_IO_CTRL

   lda #<event
   sta kernel.args.events
   lda #>event
   sta kernel.args.events+1

   jsr init_music
   jsr SetTimer

loop:
   jsr handle_events
   bra loop

handle_events:
   lda kernel.args.events.pending
   bpl done_handle_events
   jsr kernel.NextEvent
   bcs done_handle_events
   jsr dispatch
   jmp handle_events

done_handle_events:
   rts

dispatch:
   lda event.type
   cmp #kernel.event.timer.EXPIRED
   beq music_playback
   rts

music_playback:
   jsr SetTimer
   jsr play_music
   rts

SetTimer:
   inc timer_cookie
   lda timer_cookie
   sta kernel.args.timer.absolute
   sta kernel.args.timer.cookie
   lda #kernel.args.timer.FRAMES
   sta kernel.args.timer.units
   jsr kernel.Clock.SetTimer
   rts

*=$A000
   .binary "testsong.bin"

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Cheat Sheet

Edit / Preview (NTSC, correct pitch)

goattracker -N -G424 song.sng

Pack for F256K

GT2RELOC song.sng song.bin -N -G454 -LD400 -Wa0 -Z80

Internal Pack

goattracker -G454 song.sng

Press F9

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Playback in your program

JSR $A000

JSR $A003

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Tested Defaults for the F256

SID: $D400
Player: $A000
Zeropage: $80/$81
Timing: NTSC (60 Hz)

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End of document.

GoatTracker

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