I went that route a while back and found a lot of weird little hitches. Keys that just wouldn’t remap and insisted on doing weird shit because of something set up in the factory ROM. Never mind the additional hassle of trying to get software to implement various layer swapping stuff if you want that - the QMK firmware has that built in.

Sure, you could just pull out the existing hardware and replace it. Sometimes it’s easier to just start from scratch though.

Keyboard controllers are usually ROM (perhaps even fixed function, they certainly used to be) controllers, so these solutions are generally software macros, like the one you linked, which works for some things, but not others.

Right, but what's the difference? I.e. if the keyboard sends "9" but software captures that and sends out "cntrl-shift-3" it's the same outcome as if the keyboard sent "cntrl-shift-3" - is it not?

If we really want custom hardware involved, the most economical solution would probably be a USB repeater that did the re-interpreting in hardware.

Then keycode & keysym correspond to different characters (or whatever) and whether or not you get the desired outcome depends on the implementation of the software capturing it at any given time.

Took me a while to work out that the reason my pasted passwords would occasionally not work was the remapping of a couple of symbol keys. (I'm accustomed to a weird mashup of USA/UK layout, thanks mainly to Apple's non-standard 'UK' layout donating Americani?ms, but then useless prominent keys I swapped for something more helpful (backtick & pipe I think, off the top of my head, for things so useless that I literally never use them and don't know their names.))

This really only works in the most trivial of cases. There just isn't enough symbol-space information in a basic keyboard to be able to implement many QMK hallmarks like level shifting, chords, momentary hold effects, and taps.

I have thought about custom in-line hardware but that's honestly as complicated as QMK. Plus latency.

What I would love however is an inline monitor to see what keycodes I'm issuing. It gets...zany.

Don't need "custom" in-line hardware. Just get this. https://www.1upkeyboards.com/shop/controllers/usb-to-usb-con...

> What I would love however is an inline monitor to see what keycodes I'm issuing.

this is actually very simple to do with QMK if you have a board with an OLED display. it's also implemented in the default keymap for a bunch of the split ergo boards (Lily58 is one that has it)

Windows: HID Macros[1], AutoHotKey[2]

Mac: Karabiner-Elements[3]

*nix: idk but should be plentiful ways

PC DOS: you’re probably out of luck

1: http://www.hidmacros.eu/

2: https://www.autohotkey.com/

3: https://karabiner-elements.pqrs.org/

Obvious problem: it depends on software. So this can't send privileged keystrokes, and doesn't work across operating systems. Some software intentionally ignores keyboard events sent by stuff like Autohotkey.

What do you do when you want to type "9" though?

The software he mentioned stores macros for each keyboard. So you can still type 9 on your main keyboard.