NUX NEK-100: nux-dsp-mod

The NEK-100's DSP is a Dream SAM5xxx chip. Its control CPU runs a 16-bit, word-addressed instruction set similar to Dream's P16, with no public documentation. I inferred it from the firmware and marked every instruction either as confirmed, when a patch using exactly that form behaved as predicted on the instrument, or as a hypothesis.

The disassembler and assembler round-trip the firmware byte for byte, whatever is still unknown. That makes patching safe to iterate: a working experiment becomes a small patch file that contains my own instructions and short checks of the bytes it expects, not the vendor's code.

Most patches fix things I ran into while playing. A user preset can load at power-on instead of the factory default. Touch gets an OFF mode with fixed velocity and an optional CUSTOM curve. Each part gets its own octave, so a split's left hand reaches the lowest bass. With sustain_midi_out the pedal's CC64 also reaches the NUX wireless dongle, which the stock firmware only does for the panel's Sustain key.

• Separate auto-off times on battery and on cable
• Startup with the settings you had when you switched off
• Display backlight timeout and an optional usage log for battery measurements

With a watt meter on a NEK-100 with a full battery: about 2.0–2.1 W on with the speaker on, about 1 W with the speaker off, and about 0.5 W asleep. The speaker amplifier takes about half of the power, so switching it off after a silence saves the most. Sleep slows the chip's clock and halves what is left. The backlight made no measurable difference.

Up to four instruments from SoundFont 2 files can replace any of the 500 sounds. The tools take over key ranges, tuning and loops and build the rest from a template sound of your own soundbank, so the result contains no NUX data. The repository ships one instrument, a meowing Cat Piano made from a CC0 recording.

Grander Piano is the factory grand with a loop added to its samples from F#4 up, which stock fade by 30 dB within a second even with the key or pedal held. Filters, LFOs and chorus from SoundFonts are not supported yet.

Yes. The DOOM demo runs on the NEK-100 itself, on its 128×64 one-bit screen, with its music played by the piano's own synthesizer. It is a DOOM-style engine of my own, not id's Doom code, which needs 32-bit arithmetic and far more RAM than the piano has. The engine is written in C, renders Doom-format BSP maps and is built with p16cc, a small C compiler I wrote for the control CPU of the piano's Dream DSP chip.

It went in steps. First a test card and a game loop at 20 frames per second on the real piano: a whole frame takes about 0.2 ms to copy and an LCD refresh about 0.8 ms. Then came a raycaster, and then the BSP engine. During development a browser emulator runs the same compiled instructions, but its timing says nothing about the piano's, so I give no frame rate for the demo.

What you can install is a demo, not the full game: one map of my own, Hangar, with Freedoom's textures, sprites and music under the BSD licence, four enemy slots, pistol and shotgun, doors, a lift and an exit switch. Because the map and the assets are free, it can be shared, and it ships as the optional doom_demo patch in the web patcher.

• C3/E3 turn, C#3 or D#3 forward, D3 back
• Freedoom's intro on the title screen, E4M8 looping in the level
• Started from Extra > DOOM, any panel key leaves