[0efe297] | 1 | Buchla 700 Hardware Emulator
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| 2 | ----------------------------
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| 3 |
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| 4 | This repository, buchla-emu.git, contains a software emulation of the
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| 5 | Buchla 700's hardware.
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| 6 |
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| 7 | It is minimalistic; it emulates just enough of the hardware to be able
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| 8 | to run the firmware from the companion repository, buchla-68k.git.
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| 9 |
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| 10 | We don't have access to original hardware, so this is our best guess
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| 11 | based on the firmware source code published by Lynx Crowe - the
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| 12 | firmware's developer - via Aaron Lanterman:
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| 13 |
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| 14 | http://lanterman.ece.gatech.edu/buchla700/
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| 15 |
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| 16 | See the buchla-68k.git repository for the firmware source code.
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| 17 |
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| 18 |
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| 19 | Building the emulator
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| 20 | ---------------------
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| 21 |
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| 22 | The emulator uses SDL2, an abstraction layer for low-level machine
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| 23 | access on Linux, OS X, and Windows. It can be obtained from the
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| 24 | project's website:
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| 25 |
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| 26 | https://libsdl.org/
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| 27 |
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| 28 | Currently, the emulator supports Linux and OS X. A port to Windows
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| 29 | should be pretty easy, given that it doesn't use any platform-specific
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| 30 | features, just C99 and SDL2.
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| 31 |
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| 32 | Our Makefile expects SDL2 to reside in /opt/sdl2. This is how we
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| 33 | typically install it:
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| 34 |
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| 35 | tar zxvf SDL2-2.0.5.tar.gz
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| 36 | cd SDL2-2.0.5
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| 37 |
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| 38 | mkdir build
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| 39 | cd build
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| 40 |
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| 41 | ../configure --prefix=/opt/sdl2
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| 42 | make
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| 43 | make install
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| 44 |
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| 45 | Now that we have SDL2 in place, invoke
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| 46 |
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| 47 | make buchla
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| 48 |
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| 49 | from the top-level directory of this repository to build the emulator.
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| 50 |
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| 51 |
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| 52 | Emulated hardware
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| 53 | -----------------
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| 54 |
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| 55 | Here's what we emulate:
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| 56 |
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| 57 | * Motorola 68000 CPU. This is actually the Musashi CPU emulator by
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| 58 | Karl Stenerud:
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| 59 |
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| 60 | https://github.com/kstenerud/Musashi
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| 61 |
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| 62 | * Motorola MC6840: Timers.
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| 63 |
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| 64 | * Motorola MC6850: Serial console and MIDI ports.
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| 65 |
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| 66 | * Epson SED1335: LCD controller.
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| 67 |
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| 68 | * Intel 82716: Video chip.
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| 69 |
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| 70 | * National Semiconductor LMC835: Equalizer.
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| 71 |
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| 72 | * General Instrument AY-3-8910: A sound chip, which is not used for
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| 73 | sound generation, but only for its I/O ports. It connects the CPU
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| 74 | to the above equalizer chip.
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| 75 |
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| 76 | * Western Digital WD1772: Floppy disk controller.
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| 77 |
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| 78 | * A few LEDs.
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| 79 |
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| 80 | * Item X: A program running on a microcontroller. It converts the
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| 81 | analog signals from the Buchla's controller pads to digital
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| 82 | values.
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| 83 |
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| 84 | Neither the program, nor the microcontroller are known, but the
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| 85 | protocol (known from the firmware source code) is pretty simple
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| 86 | and self-explanatory.
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| 87 |
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| 88 | * Item Y: The actual sound generator, referred to by the firmware
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| 89 | source code as "the FPU." This could actually be two chips:
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| 90 |
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| 91 | 1. One chip, maybe a DSP, for generating the 15 different
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| 92 | parameter envelopes for each of the 12 voices:
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| 93 |
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| 94 | - 4x FM modulator (oscillator) frequency.
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| 95 |
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| 96 | - 6x FM modulator (oscillator) envelope.
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| 97 |
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| 98 | - 1x Output signal amplitude envelope.
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| 99 |
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| 100 | - 1x Output signal filter envelope.
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| 101 |
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| 102 | - 1x Output signal filter resonance envelope.
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| 103 |
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| 104 | - 1x Output signal stereo location.
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| 105 |
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| 106 | - 1x "Dynamics." (TBD - currently not emulated.)
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| 107 |
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| 108 | Over time, the chip interpolates between the points of the
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| 109 | envelopes drawn in the MIDAS VII instrument editor.
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| 110 |
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| 111 | 2. A second chip for the actual sound generation. This is likely
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| 112 | a DSP, possibly a Hitachi HD61810, which supports a 16-bit
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| 113 | floating-point format that's also found in the firmware
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| 114 | source code (12-bit mantissa, 4-bit exponent).
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| 115 |
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| 116 | This chip takes in the current levels of a voice's envelopes
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| 117 | and, based on them, performs the FM synthesis for this voice
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| 118 | by modulating the user-drawn carrier waves A and B according
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| 119 | to the selected FM configuration (algorithm).
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| 120 |
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| 121 | We don't know how many of the envelopes not related to FM
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| 122 | (e.g., the filter) are actually used digitally. At least some
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| 123 | of the envelopes probably control analog circuits.
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| 124 |
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| 125 | Obviously, the emulator does everything digitally.
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| 126 |
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| 127 | This "two chip" hypothesis would be in line with the "four
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| 128 | computers" marketing claim from the Buchla 700 marketing copy. The
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| 129 | four "computers" would be the Motorola 68000, the microcontroller
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| 130 | that does the A/D conversion of the pad inputs, plus the two CPUs
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| 131 | that constitute "the FPU."
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| 132 |
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| 133 | If you have access to an actual Buchla 700, please do contact us. It
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| 134 | would be great to be able to compare the emulation to real hardware.
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[ed545d5] | 135 |
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| 136 | If it's non-functional, this is also fine. We might be able to gain
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| 137 | some insights from reading the FPU microcode PROMs.
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