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

Pitch and playback speed are 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.

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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

Always start GoatTracker with:

goattracker -G454 song.sng

Important: .sng files store tuning. Loading after startup will overwrite the setting.

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4. Packing the Song

Songs must be packed into a self-playing binary.

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Option A: Internal Pack (F9)

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

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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
- -Wa0 = $A000
-Zxx uses two bytes
- $80/$81 is tested and safe
- Avoid $F0–$FF (kernel use)
-Wxx and -Zxx are configurable

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5. Playing the Music

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5.1 Initialization

Call the init routine:

JSR $A000

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5.2 Per-Frame Playback

Call once per frame:

JSR $A003

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6. Additional Notes

-N controls speed
-Gxx controls pitch
Both are required
The binary is C64-compatible
Correct setup ensures compatibility

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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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; ============================================================================
; 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

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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