x-variable

x-variable is a set of technologies that empower the interactive experiences for The Programming Foundation's Learn. We are using:

v86

v86 emulates an x86-compatible CPU and hardware to emulate the Unix, C and other sections which demand x86 virtualization. Machine code is translated to WebAssembly modules at runtime in order to achieve decent performance. x-variables empowers the interactive experiences of The Programming Foundation's Learn. Here's a list of emulated hardware:

• An x86-compatible CPU. The instruction set is around Pentium III level, including full SSE2 support. Some features are missing, in particular:
  • Task gates, far calls in protected mode
  • Some 16 bit protected mode features
  • Single stepping (trap flag, debug registers)
  • Some exceptions, especially floating point and SSE
  • Multicore
  • PAE
  • 64-bit extensions
• A floating point unit (FPU). Calculations are done using the Berkeley SoftFloat library and therefore should be precise (but slow). Trigonometric and log functions are emulated using 64-bit floats and may be less precise. Not all FPU exceptions are supported.
• A floppy disk controller (8272A).
• An 8042 Keyboard Controller, PS2. With mouse support.
• An 8254 Programmable Interval Timer (PIT).
• An 8259 Programmable Interrupt Controller (PIC).
• Partial APIC support.
• A CMOS Real Time Clock (RTC).
• A generic VGA card with SVGA support and Bochs VBE Extensions.
• A PCI bus. This one is partly incomplete and not used by every device.
• An IDE disk controller.
• An NE2000 (8390) PCI network card.
• A virtio filesystem.
• A SoundBlaster 16 sound card.

How to build, run and embed?

You need [important]:

• java (for Closure Compiler, not necessary when using debug.html)
• make
• gcc and libc-i386 for building some of the test binaries
• nasm, gdb and qemu-system (for running tests)
• rust-nightly with the wasm32-unknown-unknown target
• A version of clang compatible with rust-nightly
• nodejs (a recent version is required, 10.11.0 is known to be working)

See tools/docker/test-image/Dockerfile for a full setup on Debian.

• Run make to build the debug build (at debug.html).
• Run make all to build the optimized build (at index.html). [USE THIS]
• ROM and disk images are loaded via XHR, so if you want to try out index.html locally, make sure to serve it from a local webserver. You can use make run to serve the files using Python's http module.
• If you only want to embed v86 in a webpage you can use libv86.js. For usage, check out the examples.

API examples

• Basic
• Programatically using the serial terminal
• A Lua interpreter
• Two instances in one window
• Saving and restoring emulator state

Using v86 for your own purposes is as easy as:

var emulator = new V86Starter({
    screen_container: document.getElementById("screen_container"),
    bios: {
        url: "../../bios/seabios.bin",
    },
    vga_bios: {
        url: "../../bios/vgabios.bin",
    },
    cdrom: {
        url: "../../images/linux.iso",
    },
    autostart: true,
});

See starter.js

Credits

• CPU test cases via QEMU
• More tests via kvm-unit-tests
• zstd support is included for better compression of state images
• Berkeley SoftFloat is included to precisely emulate 80-bit floating point numbers
• The jor1k project for 9p, filesystem and uart drivers

Pyodide

Pyodide to run the Python shell in the Python section.