I made a patch for proper Ctrl-Break handling. This is useful for MS-DOS or compatible operating systems like FreeDOS.
When Ctrl-Break is detected, it clears the keyboard buffer, sets the Ctrl-Break flag at [0040h:0071h], invokes int 1Bh and then adds 0000h to the keyboard buffer. If a non-enhanced keyboard is present, Ctrl-Scroll Lock works just like Ctrl-Break. This seems to be the "standard" BIOS behaviour, at least on the PCs I tested.
The patch was tested with MS-DOS 6.22, running under qemu.
I'm new to git (and this is my first SeaBIOS patch ever), so I'm not sure what's the preferred way to submit patches. I just did a "git diff" and attached the result. Sorry if that's not the best way :)