liboplhw: A library for using real OPL2 synth chips

liboplhw is a library which provides access to real OPL2 chips on a number of different hardware/software platforms:

• The OPL2LPT parallel port OPL2 soundcard
• The Retrowave OPL USB soundcard
• Any OPL2 soundcard supported by the Linux kernel via ALSA
• Retro soundcards via direct I/O port access (as root)

Note that, unlike many other projects which provide direct access to the OPL2 under Linux, liboplhw's ALSA backend does not require access to the direct I/O ports, and so applications do not need to run as root (so long as the user has permission to access the sound card, e.g. by being in the audio group).

liboplhw can be built as a static library (default), as a shared library (with cmake -DBUILD_SHARED_LIBS=ON), or the files can be included directly in your project.

liboplhw's website is available at: https://davidgow.net/hacks/oplhw.html And the source code can be found at: https://github.com/sulix/liboplhw

Installation

To install liboplhw, configure it with CMake, then make install.

1. Make a build directory: $ mkdir build/ ; cd build
2. Configure it with CMake: $ cmake .. (Note that you may want to set a different installation prefix here with -DCMAKE_INSTALL_PREFIX=<prefix>, for example /usr)
3. Compile it: $ make
4. Install it: $ sudo make install

Finding the device name

liboplhw supports a number of different protocols, each with their own URI scheme.

For ALSA devices, to find the device name to use on your system, you'll need the 'card' and 'hwdep' numbers for your device. The card number is the index of the soundcard (you can often find it in aplay -l), and the hwdep number is almost always 0. To make sure, just look in /proc/asound/hwdep and look for an entry titled "OPL3 FM" or "OPL2 FM". The card number and hwdep number will be printed beforehand. The device name is then just "alsa:hw:${card},${hwdep}". For example, "alsa:hw:0,0". You can also leave the device name as "alsa:" to pick the first available OPL2/3 FM synth.

For OPL2LPT parallel port devices, you use the URI scheme "opl2lpt:", followed by the name of the parallel port. For example, "opl2lpt:parport0". OPL3LPT devices should work as well, but will only operate in OPL2 mode.

For Retrowave OPL USB devices, use "retrowave:" followed by the path to the serial device, such as "retrowave:/dev/ttyACM0".

To use raw I/O port access (not recommended), use the "ioport:" device. You'll need to run as root, or otherwise have I/O access (which may be disabled entirely on some kernels, particularly if secure boot is enabled). If your soundcard's OPL port is not the standard (388h), you can provide another in hex, such as "ioport:c050" for the C-Media CMI8738. PCI(e) soundcards usually have their FM ports at their base address plus 50h.

Using the API

You can use liboplhw really easily. There are only three functions to worry about:

• oplhw_OpenDevice(const char *dev_name) Opens an OPL2 device. Returns an oplhw_device pointer, and accepts the device name as input.
• oplhw_Write(oplhw_device *dev, uint8_t reg, uint8_t val) Writes the byte val to OPL2 register reg on device dev
• oplhw_CloseDevice(oplhw_device *dev) Closes the device once you've finished using it.

Just #include <oplhw.h>, and link against liboplhw with: pkg-config --cflags --libs oplhw