Gemini FM is a music replayer for the MSX series of computers. It aims to support one song format for two sound chips: the Yamaha OPLL (Panasonic FM-PAC and derivatives) and Yamaha OPM (Yamaha SFG-01 and derivatives). Gemini FM imposes some minor limitations on OPLL usage and major limitations on OPM usage in order to create a sound module format that works for both chips. The hope is that developers and composers looking to add OPLL music to their MSX games will accept these limitations to instantly also support the much less commonly supported OPM as well. Composers may then take it a step further and replace some OPM voices with secondary voices that sound more less like their OPLL counterparts. This will allow composers to use the additional features of the OPM still without needing to do a second arrangement or include two sets of music data per song.

The MSX has many many sound add-ons, but most are not widely supported perhaps because they are not widely owned, and perhaps still not widely owned because they are not widely supported. Gemini FM hopes to solve this chicken-and-egg problem for one of the MSX's oldest and coolest sound modules.

Gemini FM is still in developement. Most OPLL and OPM functions have been implemented, but everything needs testing and fine tuning. There may be timing-related bugs in the player still. Once the MSX-DOS replayer is complete, a standalone binary blob for use in games will be created, as well as tools to create Gemini FM performance data. Currenly being considered are web-based MIDI converters and MML compilers.

Gemini FM is written in a programming langauge called PARASOL. PARASOL is available here. The PARASOL compiler is a CP/M-80 program, so it must be used on a CP/M-80 device or in an emulator such as iz-cpm. While CP/M programs are largely compatble with MSX-DOS, the PARASOL compiler has a number of issues with it so compiling on MSX may not work correctly. To compile in CP/M, enter the directory containing the SRC file and the compiler and type:

PARASOL GEMINIFM.COM

Or to compile using iz-cpm without actually entering the CP/M command line on your hip and fancy modern machine, enter the directory containing the SRC file and the compiler and type:

IZ-CPM PARASOL.COM GEMINIFM.COM

Either of these will create the GEMINIFM.COM executable for use in MSX-DOS.

One of the eventual goals for Gemini FM is multiple music making tool options to suit different users and needs. For now, the only user is me and the only need is testing, so a terrible music making tool is sufficient. That is GFMASM, which is to an MML compiler what an assembler is to a high level langauge compiler. Syntax is subject to change as the playroutine evolves.

Below is the syntax for writing music in GFMASM. Bracketted letters are the only letters required, so you can write a set instrument command as INST 0 1, or I 0 1, or ILLINOIS 0 1 if you so chose. Please only user upper case letters and place only one command per line.

See EXAMPLE.TXT in latest release for an example of GFMASM input.

Music data for Gemini FM is stored in pairs of bytes, the first of which containing a bytecode and the second of which containing data. This is subject to change as the playroutine evolves. The list of bytecodes and their expected data is as follows:

All values 0-255 unless otherwise stated.

Infinte loops are used to loop a song infinitely, as the name suggests. Repeats will only repeat a section once, but repeats can be nested within themselves and within an infinite loop.

This convienently corresponds to the data format that is written directly to the OPLL's rhythm register. The OPM can only play two drums at once in this configuration, but the sound driver will prioritize your five logical drums into the two drums that sound. OPM channel 6 will play toms and bass drum, giving bass drum priority. OPM channel 7 will play cymbals, snare, and hi-hat, giving priority in that order.

The OPLL has fifteen preset voices and one user voice, which in this engine is hardcoded as a bell. The first half of the OPM sound bank is approximations of these OPLL voices, while the second half are either alternative versions that take advantage of the OPM's enhanced FM synthesis capabilities or alternate instruments altogether. By using only the insturments up to 0x10, you will have a song that sounds roughly the same on both chips, while using the second set of voices will allow you to better utilize the OPM without breaking compatability with the OPLL.