Keyboard: Compress keymaps about x16-rom HOT 4 CLOSED

WIP https://github.com/commanderx16/x16-rom/tree/compressed_keymaps

from x16-rom.

I am no longer convinced of this:

• Mapping everything onto 48ish codes might work, but there could be a keyboard layout that I'm not aware of now that doesn't fit into this.
• We have plenty of ROM space now and could use more than one bank for keymaps.
• We will support user-defined keyboard layouts (#258), so the user can always have the autoboot script load a layout from disk.
• If we reserve ~600 bytes in banked RAM for a loadable keyboard layout anyway, we might as well store compressed layouts in ROM and decompress one into RAM. A quick test got 630 bytes down to 349 bytes for "en_US". This way we can store about 23 keymap pairs (PET & ISO) on 16 KB ROM bank.

from x16-rom.

#258 just defined a fixed keytab format at a fixed banked RAM location.
The next step would be to store the layouts in ROM compressed using the KERNAL's LZSA support. And then to add more layouts.

LZSA gets the 1302 byte keymaps down to 438-478 bytes (average: 459). Plus 8 bytes index header. That's about 35 keyboard layouts. (The previous calculation assumed we'd compress PET and ISO separately.)

from x16-rom.

I asked users in the forum
https://www.commanderx16.com/forum/index.php?/topic/2782-keyboard-layout-survey/
and on FB
https://www.facebook.com/groups/CommanderX16/posts/1158745751543184
what keyboard layout they use. I already did that back in 2019, but maybe I can get a better signal now.

from x16-rom.