Overview
- Object ID : 2862 (2024-03-13 21:12:44)
- Author : Wuerfel_21
- Content : Code
- Microcontroller : Propeller 2
- Languages : PASM2, SPIN2
- Category : Speech and Sound
- Licence : Other
- Tag : emulation
Content
(or SEGA Genesis if you're in yankland...)
This is an emulation of the Yamaha "OPN2" YM2612 FM synth chip that runs in one P2 cog.
Features:
- 6 channels of 4-operator phase-modulation synthesis
- All 24 oscillators updated at the same rate as the real chip (~53 kHz)
- Channels are not mixed, but multiplexed onto the DAC, like in the real chip.
- Emulates DAC distortion
- Emulates output lowpass filter
- Supports SSG-EG
- Mostly supports CH3 special mode (rate scaling doesn't account for it)
- Supports CH6 raw DAC mode
- Bonus: SEGA PSG (SN76489 variant) emulation!
Misfeatures:
- Envelope generators are updated at 1/12 the real rate (~1.5kHz instead of ~18 kHz)
This causes slight clicking on certain envelope rates and other artifacts.
The Ultra version runs at 1/2 real EG rate and doesn't exhibit this issue. - Timers and CSM mode are not implemented.
- PSG sound is somewhat aliased due to relatively low update rate (~53 kHz) (~159 kHz in Ultra version)
- Requires at least 250 MHz P2 clock to run properly (300 MHz for Ultra version).
(Too low clock speed -> low and/or inconsistent pitch) - Some instruments sound a little off, but maybe I'm just going insane.
Still orders of magnitude better than those silly AtGames units, haha
Videos
MEGA JUKE: https://youtu.be/f650rmtDxW8
Spin API example: https://youtu.be/JRQW2tkkO0E
(Note: the spectrograph in these is not running on the P2, it's just there so it's more than a still image)
What's included
| File name | Purpose |
|---|---|
OPN2cog.spin2 |
OPN2 emulation core |
OPN2cog_ultra.spin2 |
OPN2 emulation core (higher quality version) |
OPN2_ROM.DAT |
OPN2 logsin/exponent ROM |
megajuke.c |
MEGA JUKE program. |
MEGAJUKE.DAT |
MEGA JUKE data file. |
megajuke_builder.rb |
Script for building MEGAJUKE.DAT |
megajuke_tracks.yml |
Track list for MEGA JUKE. Add your own favorite tunes! |
ExampleSpinAPI.spin2 |
Example that plays a weird little tune using the Spin API and VGI patch files |
*.vgi |
VGI patch files used by the Spin API example |
ExampleVGMPlay.spin2 |
In-memory VGM player. Copy a VGM file from the tunes directory and load it! |
ExampleSSG-EG.spin2 |
Example/test that plays a note normally and then with all 8 SSG-EG modes |
tunes.zip |
Folder of lots of VGM dumps! But zipped to not pollute the Git repo as much. |
romgen.rb |
Script for building OPN2_ROM.DAT |
eg_analyzer.rb |
Script for computing the EG rate lookup tables |
lfo_analyzer.rb |
Script for computing the LFO FM lookup table |
logo.gal |
GraphicsGale layered file for the logo |
Running MEGA JUKE
The MEGA JUKE program streams register dumps from a file, using the 9P server in loadp2 (in theory, replacing _vfs_open_host with _vfs_open_sdcard should make it run from SD card, too, but in practice it hangs after reading the track text, IDK why. SD code is probably not quite thread safe)
- Have the latest flexspin/flexprop (5.4.3) installed
- Unzip
tunes.zip - Open
megajuke.cand edit the pin constants near the top. - Compile with
flexspin -2 megajuke.c -D_BAUD=2000000 - Load with
loadp2 -p [your port here] -t -9 . -b 2000000 megajuke.binary