dwhinham/mt32-pi v0.7.0 on GitHub

FluidSynth synthesizer engine v2.1.5 for using SoundFonts for General MIDI support and more.
- You can switch between MT-32 and SoundFont mode at runtime using SysEx.
- SoundFonts can be switched at runtime using SysEx, with some caveats for large SoundFonts (see FAQ section of README).
- New configuration file options for changing default synthesizer and SoundFont.
GeneralUser GS v1.471 included as default SoundFont - many thanks to S. Christian Collins for kindly giving permission!
Ability to invert the display orientation for SSD1306 (new configuration file option).
Support for 64 pixel high SSD1306 OLED displays - many thanks to @ctrl_alt_rees for donating a screen!
Ability to set I2C clock speed (new configuration file option).
- This is useful for allowing larger displays to refresh at a faster speed; see config file for details.
Power saving mode with configurable timeout (new configuration file option).
- The CPU clock speed will be lowered, audio device stopped, and LCD backlight turned off (when possible) after a configurable number of seconds to save energy.
- Any MIDI activity will instantly bring the system out of power saving mode.
Undervoltage/throttling detection - mt32-pi will now warn the user when the firmware detects an undervoltage/CPU throttling condition.

Update to circle-stdlib v15.4.
New multi-core architecture; audio rendering and LCD updates moved to their own dedicated CPU cores, leaving MIDI and interrupt processing on the primary core.
Kernels for Pi 3 and 4 are now compiled for AArch64 (64-bit) for better performance.
- When upgrading, you must replace the config.txt file on your SD card and add the new armstub8-rpi4.bin file for Pi 4.
- You should remove old kernel*.img files from your SD card.
- It's recommended that you clear your SD card (except for your roms directory) and reconfigure mt32-pi for this release.
Synth engines now compiled with more aggressive optimizations enabled to benefit from ARM NEON instructions.
Due to the above three changes, it's possible that Raspberry Pi 2 may be more usable with this release, but this is untested.
Kernel size significantly reduced by removing mt32emu ROM loader dependency on C++ iostreams.
Improved layout of 4-line HD44780 LCD.
- MT-32 status line moved to bottom row.
- Part levels now 3 rows high.
Default sample rate and chunk size reduced to 48000Hz and 256 samples.

SSD1306 text alignment was off by one pixel.
SSD1306 part level meters' top pixels would flicker with long sustained notes.
Part level meters would suddenly snap to a lower level if a quiet note followed a loud note instead of falling off.
Possibility of overflowing text in HD44780 Print() function.