Crosstalk

Crosstalk is a collection of tools for building custom computer architectures, register-transfer-level designs and the software that runs on them. It provides a sandbox containing both a simulator and an emulator, and players can use it to construct and program anything from a calculator or LED controller to a full computer. The package includes a gate-level SystemVerilog simulator, an elaborator, a synthesiser and a C emitter, alongside the Clang compiler, which builds the emitted C code so that designs can be executed more quickly. A typical session involves opening the RTL workspace, starting a shell, describing a design in SystemVerilog, programming it and then writing software to run on it.

Designs can be run in several ways: as a standard RTL simulation, as generated C99 compiled with the bundled Clang, in a behavioural emulation mode that trades accuracy guarantees for speed, or through a slower gate-level simulation of a synthesised version that is limited to smaller designs. Supporting tools include a memory view of the running design, an oscilloscope that can be attached to any signal, a profiler showing where cycles are spent, and an interactive schematic viewer covering both RTL and gate-level views. Designs with video output can drive one of three display types (CRT, gas-plasma or LCD) using CGA or VGA interfaces, and these in-game displays are interactive. Serial communication is supported through virtual in-game ports, the host machine’s physical serial ports (ttyUSB and ttyACM devices on Unix, COM ports on Windows) or Crosstalk’s own shell, so real microcontrollers, sensors, buttons or other computers can be connected to a design. A truecolour terminal emulator compatible with ANSI, VT100, xterm and kitty is included and can act as a serial I/O device.

The game ships with its own instruction set architecture, the Minimal Instruction Set Computer (MISC), together with a reference CPU called the DANGLING Logic Unit, and the bundled LLVM can compile code for it. Players may also define their own ISAs, with an in-game help banner, register state overview, stack trace on faults and a program-level profiler available during development. Sandbox mode is the default and offers a workspace of resizable floating windows; a networked submode uses Steam Networking so several people can build together. Designs, software and emulators can be shared through the Workshop. A free DLC containing a native MISC game, Hardware Sniffers, and a later DLC adding a guided ISA design feature set are both planned.