snake-bios

A snake game made entirely in the BIOS.

Based on my other snake game.

It's 114 bytes including all the code used to initialize the hardware (the rest of the BIOS is filled with zeros).

Running

I can't show a demo using QEMU because I couldn't find any online tool to imitate QEMU.

That's why I'm using the V86 x86 emulator.

However, when making this game I found a couple of differences between what QEMU and V86 require.

I didn't want to take the easy route so that's why the code is filled with those %ifdef QEMU and %ifdef V86.

This makes it possible to compile for QEMU compatibillity, V86 compatibillity or both.

Online demo

The V86 version of the BIOS is 116 bytes (ignoring the last 4 bytes because we need them just because of a V86 bug as detailed in the comments).

You can try the game in the online demo.

Use the arrow keys on PC or swipe on mobile.

The libv86 and v86 are genrated like so:

cd v86
git clone --depth 1 https://github.com/donno2048/v86
cd v86
make all
cp build/libv86.js build/v86.wasm ..
cd ..
rm -rf v86

Self-hosting

Compiling

We're compiling for QEMU only so use -D QEMU.

nasm bios.asm -o snake.raw -D QEMU

Run

qemu-system-i386 -display curses -bios snake.raw -plugin contrib/plugins/libips.so,ips=2000

For some reason the ips plugin doesn't come with QEMU so we have to build QEMU from source to use it (or go here):

git clone --branch stable-9.2 --depth 1 https://github.com/qemu/qemu
cd qemu
./configure --target-list=i386-softmmu --enable-curses --enable-plugins --disable-docs
make all
ls build/

You might need to install QEMU build dependencies:

apt install gcc libglib2.0-dev libfdt-dev libpixman-1-dev zlib1g-dev ninja-build qemu libncurses5-dev libncursesw5-dev python3-venv python3-pip -y
pip3 install tomli

The game will take some time to initialize the hardware, then you just need to use the numpad arrows to control the snake movement.

Numpad

If you don't have a numpad you can compile with

nasm bios.asm -o snake.raw -D NONUMPAD

And then use the keypad.

Slow

If you don't want to use the QEMU ips plugin, or just want to slow the game down you can use:

nasm bios.asm -o snake.raw -D SLOW=0x5000

You can adjust the SLOW factor to fit your machine/emulator.

Font

To run the game in QEMU with standard graphics we have to include a font, as QEMU doesn't have it built-in.

I'm using CP437.F16, which was taken from https://github.com/viler-int10h/vga-text-mode-fonts/blob/master/FONTS/SYSTEM/DOSMIXED

To compile using the font use:

nasm bios.asm -o snake.raw -D FONT

QR Code

Here is the game as a QR Code (made with qrencode -r <(sed 's/\x00*$//' snake.raw) -8 -o qr.png)