Buchla 700 Hardware Emulator ---------------------------- This repository, buchla-emu.git, contains a software emulation of the Buchla 700's hardware. It is minimalistic; it emulates just enough of the hardware to be able to run the firmware from the companion repository, buchla-68k.git. We don't have access to original hardware, so this is our best guess based on the firmware source code published by Lynx Crowe - the firmware's developer - via Aaron Lanterman: http://lanterman.ece.gatech.edu/buchla700/ See the buchla-68k.git repository for the firmware source code. Building the emulator --------------------- The emulator uses SDL2, an abstraction layer for low-level machine access on Linux, OS X, and Windows. It can be obtained from the project's website: https://libsdl.org/ The SDL2 website also hosts the SDL2_net and SDL2_ttf projects, which add support for networking and TrueType fonts to SDL2 SDL2_ttf, in turn, requires the FreeType library, which is available from the FreeType website: https://www.freetype.org/ Currently, we build the emulator natively on Linux and OS X. The Windows version is cross-compiled on Linux using a x86_64-w64-mingw32 cross-toolchain. For Linux and OS X, our Makefile expects all of the above libraries to reside in /opt/sdl2. This is how we typically install them: # Build and install FreeType first tar zxvf freetype-2.7.1.tar.gz cd freetype-2.7.1 mkdir build cd build # Skip the optional features (compressed fonts, etc.) that would # create more dependencies ../configure --prefix=/opt/sdl2 \ --without-zlib --without-bzip2 --without-png --without-harfbuzz make make install # Then build and install SDL2 tar zxvf SDL2-2.0.5.tar.gz cd SDL2-2.0.5 mkdir build cd build ../configure --prefix=/opt/sdl2 make make install # Build and install SDL2_ttf, now that we have FreeType and SDL2 tar zxvf SDL2_ttf-2.0.14.tar.gz cd SDL2_ttf-2.0.14 mkdir build cd build ../configure --prefix=/opt/sdl2 \ --with-sdl-prefix=/opt/sdl2 --with-freetype-prefix=/opt/sdl2 make make install # Build and install SDL2_net last tar zxvf SDL2_net-2.0.1.tar.gz cd SDL2_net-2.0.1 mkdir build cd build ../configure --prefix=/opt/sdl2 --with-sdl-prefix=/opt/sdl2 make make install Now that we have everything in place, invoke make buchla from the top-level directory of this repository to build the emulator. The cross-build for Windows is done similarly, with the following differences when configuring the libraries: * We use "--prefix=/opt/sdl2-win" instead of "--prefix=/opt/sdl2", so that the Windows versions of the libraries go to a different directory. That's where our Makefile expects to find them when cross-building. * We additionally specify "--host=x86_64-w64-mingw32" to enable cross-compilation. Then, to cross-build the emulator, invoke make buchla.exe WIN=1 from the top-level directory of this repository. Defining the "WIN" variable selects the cross-toolchain and "/opt/sdl2-win" as the library directory. In addition to the emulator, we need to build the mkdisk utility, which we'll use to create a 720-KiB floppy disk image that can be read by the Buchla firmware. Building mkdisk works pretty much like building the emulator. On Linux and OS X, invoke make mkdisk from the top-level directory of this repository. To cross-build the Windows version, invoke make mkdisk.exe WIN=1 instead. Running the emulator -------------------- This is where this repository, buchla-emu, meets its companion repository, buchla-68k. We assume that you built the following files according to the instructions in the buchla-68k repository: bios.abs midas.abs Please copy (or symlink) them into the top-level directory of this repository, buchla-emu. bios.abs contains the Buchla 700's BIOS code. The file is loaded by the emulator directly to emulate the BIOS PROM. midas.abs is the MIDAS VII software. Unlike the BIOS, which resides in a PROM, it is loaded from a floppy disk. To create this floppy disk, we need the mkdisk utility. mkdisk expects to be run from inside the directory that contains midas.abs and produces a disk image file, buchla.disk in the same directory. For example, on Linux: ~/buchla-emu$ ls -l midas.abs lrwxrwxrwx 1 emu emu 23 Jul 30 18:07 midas.abs -> ../buchla-68k/midas.abs ~/buchla-emu$ ./mkdisk ~/buchla-emu$ ls -l buchla.disk -rw-r--r-- 1 emu emu 737280 Aug 6 09:44 buchla.disk Now we have everything in place to run the emulator. On Linux and OS X you can invoke it directly from the top-level directory of this repository: ~/buchla-emu$ ./buchla If you prefer to install the emulator elsewhere, be sure to copy the following files: buchla | buchla.exe emulator executable (.exe for Windows) ttf/vera-sans-mono.ttf emulator font bios.abs BIOS code buchla.disk disk image This also applies to copying the cross-compiled Windows emulator to a Windows machine. If you would like to keep the BIOS code, disk image, and font separate from the emulator executable, check out the emulator's -b, -d, and -f command line options. Use -h for an overview of all available options. Cross-debugging the firmware ---------------------------- While the emulator is running, it listens on TCP port 12053 for incoming connections from a GDB cross-debugger. This allows for comfortable source-level debugging of the cross-compiled BIOS and MIDAS VII code, while it runs in the emulator. We assume that you have a GCC cross-toolchain in /opt/cross-m68k, as described in the buchla-68k repository. Based on that, we build a GDB cross-debugger: # If you haven't yet done so, add the cross-toolchain to your # PATH, so that the GDB build can find it. export PATH="/opt/cross-m68k/bin:${PATH}" tar zxvf gdb-7.12.tar.gz cd gdb-7.12 mkdir build cd build ../configure --prefix=/opt/cross-m68k --target=m68k-none-elf make -j2 make install The Buchla firmware uses its own (Atari-like) object and executable file format. However, the cross-toolchain and the cross-debugger support the ELF standard. When you built the BIOS and MIDAS VII software, you ended up with two files in the Buchla's executable file format, bios.abs and midas.abs. However, the cross-build process also produces matching ELF files, bios.elf and midas.elf, suitable for the cross-debugger. Depending on whether you would like to cross-debug the BIOS or MIDAS VII, you'd specify either bios.elf or midas.elf when invoking the cross-debugger. To follow along the following example, copy (or symlink) bios.elf and midas.elf from the buchla-68k repository into the top-level directory of this repository. In order to open a debug session for the BIOS, run the cross-debugger with bios.abs and connect it to the running emulator using GDB's target remote :12053 command. 12053 is the port on which the emulator listens for incoming GDB connections. host:~/buchla-emu$ m68k-none-elf-gdb ./bios.elf GNU gdb (GDB) 7.12 Copyright (C) 2016 Free Software Foundation, Inc. [...] (gdb) target remote :12053 Remote debugging using :12053 trwzsup () at rom/bios.s:832 832 move.l 0(a0,d0),d0 | Get routine address (gdb) From here on, everything is pretty much standard GDB, for example: (gdb) break pscan Breakpoint 1 at 0x105a64: file rom/romp.c, line 3403. (gdb) cont [...] (gdb) bt #0 pscan () at rom/romp.c:3403 #1 0x00105e96 in main () at rom/romp.c:3587 #2 0x00105fd6 in Croot (cp=0x0) at prolog/croot.c:141 #3 0x00105f52 in start1 () at prolog/fsmain.s:59 (gdb) In order to debug MIDAS VII, run the cross-debugger with midas.elf, instead: host:~/buchla-emu$ m68k-none-elf-gdb ./midas.elf GNU gdb (GDB) 7.12 Copyright (C) 2016 Free Software Foundation, Inc. [...] Emulated hardware ----------------- Here's what we emulate: * Motorola 68000 CPU. This is actually the Musashi CPU emulator by Karl Stenerud: https://github.com/kstenerud/Musashi * Motorola MC6840: Timers. * Rockwell R65C52: Serial console and MIDI ports. * Epson SED1335: LCD controller. * Intel 82716: Video chip. * National Semiconductor LMC835: Equalizer. * General Instrument AY-3-8910: A sound chip, which is not used for sound generation, but only for its I/O ports. It connects the CPU to the above equalizer chip. * Western Digital WD1772: Floppy disk controller. * A few LEDs. * Item X: A program running on a microcontroller. It converts the analog signals from the Buchla's controller pads to digital values. Neither the program, nor the microcontroller are known, but the protocol (known from the firmware source code) is pretty simple and self-explanatory. * Item Y: The actual sound generator, referred to by the firmware source code as "the FPU." This could actually be two chips: 1. One chip, maybe a DSP, for generating the 15 different parameter envelopes for each of the 12 voices: - 4x FM modulator (oscillator) frequency. - 6x FM modulator (oscillator) envelope. - 1x Output signal amplitude envelope. - 1x Output signal filter envelope. - 1x Output signal filter resonance envelope. - 1x Output signal stereo location. - 1x "Dynamics." (TBD - currently not emulated.) Over time, the chip interpolates between the points of the envelopes drawn in the MIDAS VII instrument editor. 2. A second chip for the actual sound generation. This is likely a DSP. XXX - Details to be filled in. We don't know how many of the envelopes not related to FM (e.g., the filter) are actually used digitally. At least some of the envelopes probably control analog circuits. Obviously, the emulator does everything digitally. This "two chip" hypothesis would be in line with the "four computers" marketing claim from the Buchla 700 marketing copy. The four "computers" would be the Motorola 68000, the microcontroller that does the A/D conversion of the pad inputs, plus the two CPUs that constitute "the FPU." If you have access to an actual Buchla 700, please do contact us. It would be great to be able to compare the emulation to real hardware. If your Buchla is non-functional, this is also fine. We might be able to gain some insights from reading out the FPU microcode PROMs.