* Christopher Havel laserhawk64@gmail.com [170526 18:34]:
You use the Arduino IDE to program Teensies, IIRC. They might also have their own. Code is uploaded directly to a USB port on the Teensy. Have a look around --> https://www.pjrc.com/teensy/
You *probably* need a Teensy++ 2.0. That is not a guarantee, just a recommendation. I have not myself played around with Teensies, they're expensive (relative to Arduino Nano/Micro clones on eBay, and to my typical budget) and I tend to think in hardware terms far better than anything software/firmware. I can't really help you beyond what I've just written.
The computer doesn't 'see' keymapping. The computer sees a string of information that tells it what key was depressed and released and when. "Keymap" is where the key is in the matrix, which the computer doesn't care about. The computer cares that you pressed the ESC key and released it x number of microseconds later, not that it's row 1, column 1 in the matrix.
You should look up the USB HID protocol and the PS/2 keyboard protocol. Those will tell you a lot of how the computer 'sees' and 'talks to' a keyboard... and how the keyboard 'talks' back.
FWIW there are several keyboard firmware projects out there baset on Atmega32U4s (The Teensy/ Arduino Pro Micro) and others like the Teensy++. Check out QMK for example: https://github.com/qmk/qmk_firmware
Especially the hand wiring guide in the docs directory. I have built several keyboards with both arduino clones and teensy boards. Works like a charm.
Kind regards,
Christian