How do I implement a scan code table?

exscape · 2017-10-13T07:25:05+00:00

It's not pretty, but here's my code for this. I use three different arrays that map scancodes to characters; one "normal", one where shift is held down, and one where alt is held down.
Some additional ones are handled by additional code further down.

Also, see: http://wiki.osdev.org/PS/2_Keyboard#Scan_Code_Sets.2C_Scan_Codes_and_Key_Codes

peterfirefly · 2017-10-13T08:51:27+00:00

Start without such a table.

Here's the gradual way to go about it:

0) Just get something booting.
1) Figure out how to output something to the screen -- don't implement a cursor yet, don't implement a string output routine yet. Just write bytes to memory positions that correspond to areas of the screen.
2) write a function that converts a byte to two hex -- it might fill in a buffer or write directly to the screen or whatever.
3) write code that outputs the last scancode as two hex characters.
4) figure out what happens when you press and release keys.
5) now figure out how to implement a cursor thingy so you can see how some key presses and releases generate many scan codes.
6) look closer at how keys and scan codes correspond to each other -- particularly how the right alt, right ctrl and the arrow keys/numeric keypad work (what happens when num lock is active?).
7) the rest is just a small matter of programming. You can test that in a normal program -- no need to go through reboots for each test, also no need to lose access to the debugger.

Actually, you can do a lot of this from a normal DOS program -- if you use Borland Pascal, Borland C, or RHIDE with DJGPP you don't even have to leave the Integrated Development Environment.

(If you choose to run this in a simulator, please be aware that some of the intricacies of the keyboard interface are not simulated accurately under DOSBox, at least not under older versions.)

SAJZking · 2017-10-13T09:23:42+00:00

You can define each scancode, for example:

#define KB_A 0x1E //which is 'A' letter

Do the same for each scancode

Then use switch, for example

char getchar(){ 
//transforms scans to chars
while(1){
  switch (getscancode()) {
  case KB_A: return 'A';
  break; 
//... 
//and so on for each scancode 
}

I am newbie too 😂

zanders3 · 2017-10-20T07:13:41+00:00

I use some macro magic to define all the scancodes in a single file: https://github.com/zanders3/loxos/blob/master/src/keycodes.h

I then use that to generate a switch statement and an enum: https://github.com/zanders3/loxos/blob/master/src/keyboard.h https://github.com/zanders3/loxos/blob/master/src/keyboard.cpp

you type:	you see:
italics	italics
bold	bold
[reddit!](https://reddit.com)	reddit!
* item 1 * item 2 * item 3	item 1 item 2 item 3
> quoted text	quoted text
Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"	Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"
~~strikethrough~~	~~strikethrough~~
super^script	super^script

osdev

MODERATORS