SIDsynth-MiST

A standalone MOS 6581/8580 (SID) synthesizer for the MiST FPGA board. The SID sound chip is borrowed from the C64-MiSTer project and driven two ways at once:

• MIDI synth — MIDI notes arrive on the board's serial input (via opto-isolator), are parsed and voice-allocated in hardware, and play through a SID core in real time.
• .sidraw playback — a second SID core plays a tune streamed from the SD card as a .sidraw register dump, picked from an on-screen OSD menu, in parallel with the live MIDI synth.

Status

This build is an early bring-up. What works today:

• .sidraw tunes streamed from the SD card, selected via an OSD menu;
• a monophonic MIDI synth — one SID voice, last-note priority;
• no MIDI CC handling (note on/off and pitch only).

Short-term goals:

• polyphonic voice allocation across the SID's voices;
• MIDI CC controls (filter, envelope, and other SID parameters).

Layout

rtl/    SID core, MIDI front-end, .sidraw player + SD reader, OSD/video,
        DC blocker, SDM DAC, top
fpga/   Quartus project (device, pins, PLLs, SDC) + build.sh
hex/    legacy .sidraw BRAM init (unused in this build; SD streaming only)
sw/     sidraw-dump host tools (.sid -> .sidraw -> .wav)

Build the FPGA core

Quartus II 13.1 is required; the build script runs it inside a Docker image so no local install is needed:

cd fpga
./build.sh

Output lands in fpga/build/:

• sidsynth_mist.rbf — copy to your MiST SD card as core.rbf to run it.
• sidsynth_mist.sof — program over JTAG with quartus_pgm -m jtag -o "p;build/sidsynth_mist.sof".

Build the host tools

sw/sidraw-dump/ builds a triplet of CLI tools (sidraw-dump, sidraw-play, sid-play) that convert between .sid, the custom .sidraw register-dump format, and .wav. They statically link vendored copies of libsidplayfp + libresidfp, so the result is a self-contained binary:

cd sw/sidraw-dump
mkdir build && cd build
cmake ..
make -j

Play tunes from the SD card

Tunes are loaded at runtime from the SD card — no rebuild needed. Convert a .sid to the .sidraw register-dump format with the host tools and copy it to a SIDSYNTH directory on the card:

sidraw-dump your_tune.sid -o your_tune.sidraw
cp your_tune.sidraw /path/to/sdcard/SIDSYNTH/

With the card inserted, press F12 on the MiST to open the OSD menu and pick a .sidraw file. user_io mounts the selection and sidraw_sd_reader streams it on demand through a small FIFO into the .sidraw player — so tune length is bounded by the SD card, not on-chip BRAM. Stock MiST firmware is used; no custom firmware is required.

Blog

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License

The RTL in rtl/ is licensed under the CERN-OHL-S v2 (Strongly Reciprocal). The vendored libsidplayfp and libresidfp sources under sw/sidraw-dump/external/ are GPL v2 and remain under their own licenses.