When I made my original snake game some people argued the only reason it was possible, was that the PC already had the BIOS and OS on it so what I call a "58 bytes snake game" is not only 58 bytes because the BIOS and OS are each thousands upon thousands of bytes.

While it's true that without those wrappers the program wouldn't be that small, I don't think it's a valid argument, but anyways, I made a POC snake game that can work without any BIOS, bootloader, or OS, all the code, including the hardware initialization, fits in 114 bytes (and filler) and runs on QEMU.

I also commented every single line in the code so you can use it to learn about how the BIOS initializes the hardware, although I tried making it very minimal (just like the original snake game), so there is not much to see.

The main problem I encountered when making this was the icount. The icount is an optional QEMU argument that allows you to set a certain speed to the emulated machine.

I wanted to use icount=20, however, someone on the QEMU team limited the icount to 10 max although everything works just fine for icount<=30.

I made a PR to the QEMU project to fix it by raising the max of icount to 30 and doing the necessary adjustments to the code to enable it to work with the higher icount.

However, one of the devs at QEMU noted that icount is deprecated so I should use the ips plugin. The problem now was that my QEMU version (5.2.0) was incompatible with plugins, I tried changing to 9.1.0 and the plugin worked! But now my BIOS didn't output anything to the screen.

I had a hunch the problem had something to do with the changes made to the VGA protocol of QEMU between those versions, so I did a binary search between the versions and found that my program works perfectly fine up until v9.0.0-rc0.

So now all I had to do was skim through the changes made between versions 8.2.6 and 9.0.0-rc0 and find something that could lead to the screen staying empty.

I looked at diffs for a whole hour and finally, I found it, I couldn't believe I missed it all along, someone started to use the byte masking property of the graphics registers.

I quickly added an output of 0xFF08 to port 0x3CE and it indeed fixed the issue and I was able to use ips successfully.