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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

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

Pyodide

Pyodide to run the Python shell in the Python section.