https://en.wikipedia.org/wiki/Combining_character
The plan: just draw the combining character in the same space as the
previous character. This will almost certainly not work for some Unicode
blocks (tibetan?)
This commit only changes the data/memory/disk model to make some space.
As always in Mu, we avoid bit-mask tricks even if that wastes memory.
Is flush-ata-cache even needed? Reading the ATA 5 spec more closely, it
looks like it's only required by ATAPI devices! (Packet Interface is what
the 'PI' stands for!) And it's unclear if my driver actually supports ATAPI
at the moment.
Mu's keyboard handling is currently a bit of a mess, and this commit might
be a bad idea.
Ideally keyboards would return Unicode. Currently Mu returns single bytes.
Mostly ASCII. No support for international keyboards yet.
ASCII and Unicode have some keyboard scancodes grandfathered in, that don't
really make sense for data transmission. Like backspace and delete. However,
other keyboard scancodes don't have any place in Unicode. Including arrow keys.
So Mu carves out an exception to Unicode for arrow keys. We'll place the
arrow keys in a part of Unicode that is set aside for implementation-defined
behavior (https://en.wikipedia.org/wiki/C0_and_C1_control_codes#C1_controls):
0x80: left arrow
0x81: down arrow
0x82: up arrow
0x83: right arrow
The order is same as hjkl for mnemonic convenience. I'd _really_ to follow
someone else's cannibalization here. If I find one later, I'll switch to
it.
Applications that blindly assume the keyboard generates Unicode will have
a bad time. Events like backspace, delete and arrow keys are intended to
be processed early and should not be in text.
With a little luck I won't need to modify this convention when I support
international keyboards.
I spent a while building a little keyboard scancode printer:
$ ./translate ex1.mu && qemu-system-i386 disk.img
..and wondering why up-arrow was 0x48 in hex but 724 in decimal. I ended
up paranoidly poking at a bunch of crap (though there _is_ a cool chromatography-based
debugging technique in 126write-int-decimal.subx) before I realized:
- 724 just has one extra digit over the correct answer
- the 0xe0 scan code is a 3-digit number in decimal -- and the final digit is '4'
There's nothing actually wrong.
https://wiki.osdev.org/ATA_PIO_Mode#IDENTIFY_command recommends the straight-and-narrow
way, but the LBA bit shouldn't matter in drive-select during IDENTIFY command,
according to the ATA 3 spec. And it works in Qemu and bochs. It'll slightly
simplify drive parameter management.
