[0efe297] | 1 | Buchla 700 Hardware Emulator
|
---|
| 2 | ----------------------------
|
---|
| 3 |
|
---|
| 4 | This repository, buchla-emu.git, contains a software emulation of the
|
---|
| 5 | Buchla 700's hardware.
|
---|
| 6 |
|
---|
| 7 | It is minimalistic; it emulates just enough of the hardware to be able
|
---|
| 8 | to run the firmware from the companion repository, buchla-68k.git.
|
---|
| 9 |
|
---|
| 10 | We don't have access to original hardware, so this is our best guess
|
---|
| 11 | based on the firmware source code published by Lynx Crowe - the
|
---|
| 12 | firmware's developer - via Aaron Lanterman:
|
---|
| 13 |
|
---|
| 14 | http://lanterman.ece.gatech.edu/buchla700/
|
---|
| 15 |
|
---|
| 16 | See the buchla-68k.git repository for the firmware source code.
|
---|
| 17 |
|
---|
| 18 |
|
---|
| 19 | Building the emulator
|
---|
| 20 | ---------------------
|
---|
| 21 |
|
---|
| 22 | The emulator uses SDL2, an abstraction layer for low-level machine
|
---|
| 23 | access on Linux, OS X, and Windows. It can be obtained from the
|
---|
| 24 | project's website:
|
---|
| 25 |
|
---|
| 26 | https://libsdl.org/
|
---|
| 27 |
|
---|
[2f9f352] | 28 | The SDL2 website also hosts the SDL2_ttf project, which adds support
|
---|
| 29 | for TrueType fonts to SDL2. SDL2_ttf, in turn, requires the FreeType
|
---|
| 30 | library, which is available from the FreeType website:
|
---|
| 31 |
|
---|
| 32 | https://www.freetype.org/
|
---|
| 33 |
|
---|
[8e1b163] | 34 | Currently, we build the emulator natively on Linux and OS X. The
|
---|
[4f3fe48] | 35 | Windows version is cross-compiled on Linux using a x86_64-w64-mingw32
|
---|
[8e1b163] | 36 | cross-toolchain.
|
---|
[0efe297] | 37 |
|
---|
[4f3fe48] | 38 | For Linux and OS X, our Makefile expects all of the above libraries to
|
---|
| 39 | reside in /opt/sdl2. This is how we typically install them:
|
---|
[2f9f352] | 40 |
|
---|
| 41 | # Build and install FreeType first
|
---|
| 42 |
|
---|
| 43 | tar zxvf freetype-2.7.1.tar.gz
|
---|
| 44 | cd freetype-2.7.1
|
---|
| 45 | mkdir build
|
---|
| 46 | cd build
|
---|
| 47 |
|
---|
| 48 | # Skip the optional features (compressed fonts, etc.) that would
|
---|
| 49 | # create more dependencies
|
---|
| 50 |
|
---|
| 51 | ../configure --prefix=/opt/sdl2 \
|
---|
| 52 | --without-zlib --without-bzip2 --without-png --without-harfbuzz
|
---|
| 53 |
|
---|
| 54 | make
|
---|
| 55 | make install
|
---|
| 56 |
|
---|
| 57 | # Then build and install SDL2
|
---|
[0efe297] | 58 |
|
---|
| 59 | tar zxvf SDL2-2.0.5.tar.gz
|
---|
| 60 | cd SDL2-2.0.5
|
---|
[2f9f352] | 61 | mkdir build
|
---|
| 62 | cd build
|
---|
| 63 |
|
---|
| 64 | ../configure --prefix=/opt/sdl2
|
---|
[0efe297] | 65 |
|
---|
[2f9f352] | 66 | make
|
---|
| 67 | make install
|
---|
| 68 |
|
---|
| 69 | # Build and install SDL2_ttf last
|
---|
| 70 |
|
---|
| 71 | tar zxvf SDL2_ttf-2.0.14.tar.gz
|
---|
| 72 | cd SDL2_ttf-2.0.14
|
---|
[0efe297] | 73 | mkdir build
|
---|
| 74 | cd build
|
---|
| 75 |
|
---|
[d94a7be] | 76 | ../configure --prefix=/opt/sdl2 \
|
---|
| 77 | --with-sdl-prefix=/opt/sdl2 --with-freetype-prefix=/opt/sdl2
|
---|
[2f9f352] | 78 |
|
---|
[0efe297] | 79 | make
|
---|
| 80 | make install
|
---|
| 81 |
|
---|
[2f9f352] | 82 | Now that we have everything in place, invoke
|
---|
[0efe297] | 83 |
|
---|
| 84 | make buchla
|
---|
| 85 |
|
---|
| 86 | from the top-level directory of this repository to build the emulator.
|
---|
| 87 |
|
---|
[4f3fe48] | 88 | The cross-build for Windows is done similarly, with the following
|
---|
| 89 | differences when configuring the libraries:
|
---|
| 90 |
|
---|
| 91 | * We use "--prefix=/opt/sdl2-win" instead of "--prefix=/opt/sdl2",
|
---|
| 92 | so that the Windows versions of the libraries go to a different
|
---|
[8e1b163] | 93 | directory. That's where our Makefile expects to find them when
|
---|
| 94 | cross-building.
|
---|
[4f3fe48] | 95 |
|
---|
| 96 | * We additionally specify "--host=x86_64-w64-mingw32" to enable
|
---|
| 97 | cross-compilation.
|
---|
| 98 |
|
---|
| 99 | Then, to cross-build the emulator, invoke
|
---|
| 100 |
|
---|
| 101 | make buchla WIN=1
|
---|
| 102 |
|
---|
[8e1b163] | 103 | from the top-level directory of this repository. Defining the "WIN"
|
---|
| 104 | variable selects the cross-toolchain and "/opt/sdl2-win" as the
|
---|
| 105 | library directory.
|
---|
[4f3fe48] | 106 |
|
---|
[0efe297] | 107 |
|
---|
| 108 | Emulated hardware
|
---|
| 109 | -----------------
|
---|
| 110 |
|
---|
| 111 | Here's what we emulate:
|
---|
| 112 |
|
---|
| 113 | * Motorola 68000 CPU. This is actually the Musashi CPU emulator by
|
---|
| 114 | Karl Stenerud:
|
---|
| 115 |
|
---|
| 116 | https://github.com/kstenerud/Musashi
|
---|
| 117 |
|
---|
| 118 | * Motorola MC6840: Timers.
|
---|
| 119 |
|
---|
| 120 | * Motorola MC6850: Serial console and MIDI ports.
|
---|
| 121 |
|
---|
| 122 | * Epson SED1335: LCD controller.
|
---|
| 123 |
|
---|
| 124 | * Intel 82716: Video chip.
|
---|
| 125 |
|
---|
| 126 | * National Semiconductor LMC835: Equalizer.
|
---|
| 127 |
|
---|
| 128 | * General Instrument AY-3-8910: A sound chip, which is not used for
|
---|
| 129 | sound generation, but only for its I/O ports. It connects the CPU
|
---|
| 130 | to the above equalizer chip.
|
---|
| 131 |
|
---|
| 132 | * Western Digital WD1772: Floppy disk controller.
|
---|
| 133 |
|
---|
| 134 | * A few LEDs.
|
---|
| 135 |
|
---|
| 136 | * Item X: A program running on a microcontroller. It converts the
|
---|
| 137 | analog signals from the Buchla's controller pads to digital
|
---|
| 138 | values.
|
---|
| 139 |
|
---|
| 140 | Neither the program, nor the microcontroller are known, but the
|
---|
| 141 | protocol (known from the firmware source code) is pretty simple
|
---|
| 142 | and self-explanatory.
|
---|
| 143 |
|
---|
| 144 | * Item Y: The actual sound generator, referred to by the firmware
|
---|
| 145 | source code as "the FPU." This could actually be two chips:
|
---|
| 146 |
|
---|
| 147 | 1. One chip, maybe a DSP, for generating the 15 different
|
---|
| 148 | parameter envelopes for each of the 12 voices:
|
---|
| 149 |
|
---|
| 150 | - 4x FM modulator (oscillator) frequency.
|
---|
| 151 |
|
---|
| 152 | - 6x FM modulator (oscillator) envelope.
|
---|
| 153 |
|
---|
| 154 | - 1x Output signal amplitude envelope.
|
---|
| 155 |
|
---|
| 156 | - 1x Output signal filter envelope.
|
---|
| 157 |
|
---|
| 158 | - 1x Output signal filter resonance envelope.
|
---|
| 159 |
|
---|
| 160 | - 1x Output signal stereo location.
|
---|
| 161 |
|
---|
| 162 | - 1x "Dynamics." (TBD - currently not emulated.)
|
---|
| 163 |
|
---|
| 164 | Over time, the chip interpolates between the points of the
|
---|
| 165 | envelopes drawn in the MIDAS VII instrument editor.
|
---|
| 166 |
|
---|
| 167 | 2. A second chip for the actual sound generation. This is likely
|
---|
| 168 | a DSP, possibly a Hitachi HD61810, which supports a 16-bit
|
---|
| 169 | floating-point format that's also found in the firmware
|
---|
| 170 | source code (12-bit mantissa, 4-bit exponent).
|
---|
| 171 |
|
---|
| 172 | This chip takes in the current levels of a voice's envelopes
|
---|
| 173 | and, based on them, performs the FM synthesis for this voice
|
---|
| 174 | by modulating the user-drawn carrier waves A and B according
|
---|
| 175 | to the selected FM configuration (algorithm).
|
---|
| 176 |
|
---|
| 177 | We don't know how many of the envelopes not related to FM
|
---|
| 178 | (e.g., the filter) are actually used digitally. At least some
|
---|
| 179 | of the envelopes probably control analog circuits.
|
---|
| 180 |
|
---|
| 181 | Obviously, the emulator does everything digitally.
|
---|
| 182 |
|
---|
| 183 | This "two chip" hypothesis would be in line with the "four
|
---|
| 184 | computers" marketing claim from the Buchla 700 marketing copy. The
|
---|
| 185 | four "computers" would be the Motorola 68000, the microcontroller
|
---|
| 186 | that does the A/D conversion of the pad inputs, plus the two CPUs
|
---|
| 187 | that constitute "the FPU."
|
---|
| 188 |
|
---|
| 189 | If you have access to an actual Buchla 700, please do contact us. It
|
---|
| 190 | would be great to be able to compare the emulation to real hardware.
|
---|
[ed545d5] | 191 |
|
---|
| 192 | If it's non-functional, this is also fine. We might be able to gain
|
---|
| 193 | some insights from reading the FPU microcode PROMs.
|
---|