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diff --git a/docs/basic_how_keyboards_work.md b/docs/basic_how_keyboards_work.md deleted file mode 100644 index 73c3f5c5f..000000000 --- a/docs/basic_how_keyboards_work.md +++ /dev/null @@ -1,96 +0,0 @@ -# How keys are registered, and interpreted by computers - -In this file, you can will learn the concepts of how keyboards work over USB, -and you'll be able to better understand what you can expect from changing your -firmware directly. - -## Schematic view - -Whenever you type on 1 particular key, here is the chain of actions taking -place: - -``` text -+------+ +-----+ +----------+ +----------+ +----+ -| User |-------->| Key |------>| Firmware |----->| USB wire |---->| OS | -+------+ +-----+ +----------+ +----------+ |----+ -``` - -This scheme is a very simple view of what's going on, and more details follow -in the next sections. - -## 1. You Press a Key - -Whenever you press a key, the firmware of your keyboard can register this event. -It can register when the key is pressed, held and released. - -This usually happens with a [periodic scan of key presses with a frequency around 100 hz](https://github.com/benblazak/ergodox-firmware/blob/master/references.md#typical-keyboard-information). -This speed often is limited by the mechanical key response time, the protocol -to transfer those key presses (here USB HID), and by the software it is used in. - -## 2. What the Firmware Sends - -The [HID specification](http://www.usb.org/developers/hidpage/Hut1_12v2.pdf) -tells what a keyboard can actually send through USB to have a chance to be -properly recognised. This includes a pre-defined list of keycodes which are -simple numbers from `0x00` to `0xE7`. The firmware assigns a keycode to each -key of the keyboard. - -The firmware does not send actually letters or characters, but only keycodes. -Thus, by modifying the firmware, you only can modify what keycode is sent over -USB for a given key. - -## 3. What the Operating System Does - -Once the keycode reaches the operating system, a piece of software has to have -it match an actual character thanks to a keyboard layout. For example, if your -layout is set to QWERTY, a sample of the matching table is as follow: - -``` text -| keycode | character | -|---------+-----------| -| 0x04 | a/A | -| 0x05 | b/B | -| 0x06 | c/C | -| ... | ... | -| 0x1C | y/Y | -| 0x1D | z/Z | -| ... | ... | -|---------+-----------| -``` - -## Back to the firmware - -As the layout is generally fixed (unless you create your own), the firmware can -actually call a keycode by its layout name directly to ease things for you. - -This is exactly what is done here with `KC_A` actually representing `0x04` in -QWERTY. The full list can be found in `keycode.txt`. - -## List of Characters You Can Send - -Putting aside shortcuts, having a limited set of keycodes mapped to a limited -layout means that **the list of characters you can assign to a given key only -is the ones present in the layout**. - -For example, this means that if you have a QWERTY US layout, and you want to -assign 1 key to produce `€` (euro currency symbol), you are unable to do so, -because the QWERTY US layout does not have such mapping. You could fix that by -using a QWERTY UK layout, or a QWERTY US International. - -You may wonder why a keyboard layout containing all of Unicode is not devised -then? The limited number of keycode available through USB simply disallow such -a thing. - -## How to (Maybe) Enter Unicode Characters - -You can have the firmware send *sequences of keys* to use the [software Unicode -Input -Method](https://en.wikipedia.org/wiki/Unicode_input#Hexadecimal_code_input) of -the target operating system, thus effectively entering characters independently -of the layout defined in the OS. - -Yet, it does come with multiple disadvantages: - - - Tied to a specific OS a a time (need recompilation when changing OS); - - Within a given OS, does not work in all software; - - Limited to a subset of Unicode on some systems. |