CPCSyntaxError

An Amstrad CPC 464 / 6128, CPC Plus and GX4000 emulator for Windows, built around a cycle-level model of the machine's video chips.

Work in progress. The CRTC, Gate Array and monitor emulation is the mature part of the project. The user interface and most expansion hardware are still being worked on -- see Project status.

• All five CRTC types (0 HD6845S/UM6845, 1 UM6845R, 2 MC6845, 3 and 4 the Plus/cost-down ASICs), each with its own rule set taken from Longshot's Amstrad CPC CRTC Compendium and checked against his SHAKER test suite and photographs of real machines.
• Gate Array models 40007 / 40008 / 40010 and the ASICs 40226 / 40489, with per-model pixel timing, and a monitor model (CTM 640/644, CM14, GT 64/65, MM12) that locks to the composite sync the Gate Array really produces.
• CPC Plus ASIC: sprites, DMA sound, 4096-colour palette, raster interrupts, split screen, soft scroll.
• Disc (DSK/EDSK), tape (CDT/TZX/WAV), cartridge (CPR) and snapshot (SNA) loading, joysticks and game controllers.
• A debugger: breakpoints with conditions, memory watchpoints, step into / over / out, disassembly with labels, hex editor, and live views of the CRTC, Gate Array, monitor, Plus ASIC, PSG, PPI, keyboard matrix, disc controller and tape.
• A built-in assembler: RASM itself, linked in. Assemble straight into the running machine's memory (F9) and run it (Ctrl+F9).
• Dockable, resizable windows (Dear ImGui docking branch); any window can be pulled out of the main window into its own.

Screenshots

Batman Forever -- CPC 6128	Pinball Dreams -- CPC 6128
Alcon 2020 -- GX4000	Sonic the Hedgehog -- GX4000

Getting started

1. Download CPCSyntaxError-win64.zip from the Releases page, unzip it anywhere and run cpcse.exe -- or build it yourself (below).

2. The CPC 464 and 6128 firmware ROMs and the CPC Plus / GX4000 system cartridge are included, in roms/ (Amstrad have kindly given their permission for the redistribution of their copyrighted material but retain that copyright). The release zip has them beside cpcse.exe, and a source build copies them there. cpcse.exe looks for a roms folder in its working directory; another can be chosen with File → ROM folder… or cpcse.exe --roms <folder>. Files are found by name (case does not matter):

   Machine	Files needed (name must contain)
   CPC 464	464 OS, 464 BASIC
   CPC 6128	6128 OS, 6128 BASIC, AMSDOS
   464 Plus / 6128 Plus / GX4000	the Plus system cartridge, a .cpr whose name contains burning rubber

3. Pick a machine from Machine → Model, and load software from the File or Media menus, or drop a file onto the window.

Settings are saved to cpcse.ini, and the window layout to cpcse_layout.ini, next to the executable. Window → Reset layout restores the default arrangement.

Keys

Key	Action
F11	fullscreen (or double-click the picture)
Ctrl+R	reset
Ctrl+P	pause / run
F5	run / pause (in a debugger window, or while paused)
F7 / F8 / Shift+F8	step into / over / out
F9 / Ctrl+F9	assemble / assemble and run (assembler window)

Keys go to the CPC unless a debugger or assembler window has the focus.

Command line

cpcse.exe --roms <folder> starts with another ROM folder. A headless screenshot mode is also available for scripting:

cpcse.exe --shot out.bmp --model cpc6128 --frames 200 [--disk game.dsk] [--type "RUN\"GAME\n"]
          [--cart file.cpr] [--tape file.cdt] [--sna file.sna] [--crtc 0-4] [--beam]

Models: cpc464, cpc6128, cpc464plus, cpc6128plus, gx4000.

Building from source

Requirements: Windows, a MinGW-w64 GCC with C++17 (GCC 10 or later), CMake 3.16+, Ninja (optional), and the SDL2 MinGW development package (SDL2-devel-2.x.x-mingw.zip from https://github.com/libsdl-org/SDL/releases).

cmake -S . -B build -G Ninja -DSDL2_ROOT=C:/path/to/SDL2-2.x.x/x86_64-w64-mingw32
cmake --build build

or unpack the SDL2 package's x86_64-w64-mingw32 folder into third_party/SDL2 and run build.bat. The result is build/cpcse.exe, with SDL2.dll and the roms folder copied beside it; the GCC runtime is linked statically, so nothing else is needed to run it.

Source layout

src/core/      the emulation core (static library, no host dependencies)
src/gui/       the desktop front end: SDL2 + OpenGL + Dear ImGui, debugger, assembler
roms/          Amstrad firmware and the Plus system cartridge (see roms/README.txt)
third_party/   Dear ImGui (docking branch) and RASM, vendored; SDL2 is fetched separately

Project status

Area	State
CRTC types 0-4, Gate Array, monitor	Mature: rule sets from the Compendium, cross-checked by independent reference models and SHAKER
Z80, PSG, PPI, disc controller, tape	Working; not yet audited to the same depth as the video chips
CPC Plus ASIC	Working
User interface	Incomplete -- new and still being refined; expect rough edges and changes
M4 board	Incomplete
Symbiface II / III	Incomplete -- mouse and RTC only; the IDE/CF interface is not emulated
DigiBlaster / AmDrum DACs	Incomplete
Lightgun, printer, V9990 (GFX9000)	Incomplete -- partly present in the core, not exposed in the user interface

Known issues

• CRTC 2: R9 rewritten during the vertical adjustment. The Compendium's CRTC 2 chapter (§12.4.1, p.97) says that if R9 is changed during the R5 additional lines, C9 "will not transition back to 0 after the additional lines and will continue its evolution according to the new value of R9", while §11.3.1 has C4 and C9 return to 0 at the end of the additional lines. Nothing printed says how the chip reconciles the two, so CPCSyntaxError follows §11.3.1 (C9 returns to 0) until hardware evidence settles it.
• C-HSYNC width on CRTC 0 and 2. The Gate Array's monitor sync on these chips is a fraction of a microsecond longer than the Compendium's table (§14.4, p.134). The documented width is not used yet because the monitor's recovery after a short sync is not modelled, and without that model it makes some pictures worse.
• The user interface and the expansions listed as incomplete above.

Credits and licence

CPCSyntaxError is released under the MIT licence (see LICENSE). The third-party components it contains keep their own licences -- see THIRD_PARTY_NOTICES.md. Note that the built-in assembler includes the Exomizer cruncher, whose licence permits non-commercial use only. The Amstrad firmware and system cartridge in roms/ are not covered by the MIT licence (see roms/README.txt).

CRTC behaviour is sourced from the "Amstrad CPC CRTC Compendium" by Longshot (CC BY-NC-ND 4.0) and checked against his SHAKER test suite. The built-in assembler is RASM by Edouard BERGE. The user interface uses Dear ImGui by Omar Cornut and SDL2.

Amstrad CPC, CPC Plus and GX4000 are trademarks of their respective owners. This project is not affiliated with Amstrad.