This program compiles monophonic MIDI files into a 6502 executable that will play on an Apple //e.
The Apple //e has a one-bit audio system. There is a single, "soft switch" memory address ($C030) that controls the speaker. To drive the speaker coil once, you read from the address $C030. If you wish to produce 400 Hz tone, you must read from that memory address at 400 Hz. This is complicated by the fact that the //e lacks any sort of system clock, so all time keeping is accomplished by counting cycles.
note.asm contains a subroutine, note(), written in assembly, capable of playing one of 62 tones for a specified duration. It contains a "wall of nops" (no-op instruction) followed by bit $C030 which reads the soft switch and drives the speaker. The duration interval is a 32-bit integer that corresponds to the total number of wavelengths to be played. 6502 processors are 8-bit systems, so interpreting the 32-bit value is held in 4 contiguous memory registers and must be handled appropriately.
There is also an assembly routine, rest(), which can be thought of as a cycle-accurate sleep function. It similarly takes in a 32-bit duration value that specifies how many times the machine should do nothing for 2000 cycles.
Midi files are processed using a ruby script found in utils/midi.rb. midi.rb processes the note events, calculates the absolute duration of the note given a specified bpm, and then writes to a series of calls to play_note() and play_rest() to play the song on the //e.
scripts/install installs the requisite homebrew packages. You can call it directly or via make
./scripts/install
# or
make install
For MacOS only
MacOS has a command called ac, but the command line version of AppleCommander installed via homebrew aliases itself as ac. This script should find and rename the alias of the homebrew installation to aplc.
There is no make command as it should only be run on MacOS systems.
./scripts/rename-ac
Virtual ][
Virtual ][ is an Apple //e emulator that runs on MacOS.
It requires a ROM image, which must be downloaded and installed separately.
See https://virtualii.com/VirtualIIHelp/virtual_II_help.html#ROMImage
Online Emulator
If you're not on MacOS, you can try using this web-based emulator
scripts/uninstall uninstalls the homebrew packages (and deletes the renamed symlink if it exists). You can call it directly or via make
./scripts/uninstall
# or
make uninstall
# Compile to 6502
make target
# Generate wav file (For casette data transfer protocol to a physical Apple ][)
make wav
# Generate aif file (For audio transfer protocol to Virtual ][)
make aif
# Generate dsk file (Load a floppy on Virtual ][ or the web emulator)
make disk
# Do all of the above
make all