Crosstalk

Crosstalk is a set of tools for creating custom computer architectures, RTL designs and software. In its sandbox, you build and program devices such as calculators, LED controllers and complex computers using a simulator and emulator for electronics designed with HDL. The included tools include a gate-level SystemVerilog simulator, an elaborator, a synthesizer, a C emitter and the Clang compiler. The C emitter derives code from your SystemVerilog, and Clang compiles that code for faster design execution.

Create and simulate designs

The default workflow is to open an RTL workspace, enter a shell, describe and program a design in SystemVerilog, then write software for it. A tool guide appears when you create your first project, and the game includes examples, but it does not provide RTL guidance or a tutorial. You need to write your own SystemVerilog or load an existing project.

You can simulate FPGA designs using vendor-neutral SystemVerilog. For faster execution, you can emit C99 with Crosstalk’s toolchain and Clang, or use emulation mode, which reproduces design behavior without guaranteeing design accuracy. High-resolution simulation uses a synthesized version of the design in the gate-level simulator; this takes much longer and is limited to smaller designs. The interactive schematic viewer shows both RTL and gate-level schematics, and can highlight heavily used cells in profile mode. A profiler also shows where cycles are spent in an SystemVerilog design.

Sandbox modes

Sandbox mode is the default experience. In Self-play, you create a workspace with floating windows that you can resize, position and align. In Networked mode, you collaborate with other players over Steam Networking in a workspace structurally identical to Self-play, with networking enabled.

Connect and inspect hardware

Crosstalk can communicate through virtual in-game serial ports, the host machine’s physical serial interface or its own shell interface. This lets you connect external devices such as microcontrollers, sensors, physical buttons and other computers to designs, representing them with stand-in parts. The supplied truecolor terminal emulator works as a serial terminal I/O device and supports ANSI, VT100, xterm and kitty; it can also communicate with the host over a PTY or ConPTY.

Memory view and an oscilloscope are included as tools for building designs. You can inspect a running design’s memory and runtime activity, or attach the oscilloscope to a signal such as sound output.

Display and CPU design

For designs with video output, you can choose among three built-in display modes: CRT, gas-plasma and modern LCD. The CRT and gas-plasma modes use CGA interfaces, while the LCD mode uses VGA. You can define instruction set architectures (ISAs) and view a help banner while developing. Runtime tools include register-state and stack views, a program locator and a program-level profiler that shows where execution time goes.

DANGCSA and the DLU

The game includes the DANGLING Computer Superarchitecture ISA and its first CPU, the DLU, as a reference SystemVerilog implementation and an option for players who do not want to create a custom architecture. The ISA is called both DANGCSA and DANGXA because “C” and “S” sound alike when spoken. Despite its minimal design, it can run complex programs. The DLU, whose full title is “DANGLING Logic Unit: Think Correctly,” complies with DANGCSA/DANGXA and supports serial communication, text output, video, audio and MIDI.

The included LLVM can compile programs for DANGCSA/DANGXA. Its native binary format is supported by LLVM and used natively on the platform; ELF serves as a compatibility layer. Designs, software and emulators can be shared through the Workshop.