keycodes are 32-bit integers.

the low byte indicates the key itself. for printable characters (and keys with
reasonable translations to ascii control codes), this is the ascii code. for
other ones, something in the range of 0x80 to 0xef is used, seen in table 1.

the top 24 bits indicate several flags. these are seen in table 2, where bit 0
is the lowest bit of the second lowest byte of the keycode, and bit 23 is the
highest bit of the highest byte of the keycode.

the "get key" system call returns 0 if there is not a key available. it is
recommended to make the system call and, if it returns 0, yield to the scheduler
and then loop back to making the system call. this way your task does not block
the cpu while waiting for keyboard input. see the "get_key_char" function in
user.c of the "knob" library for an example of this.


table 1:

 code | key
------|---------------
 0x80 | caps lock
 0x81 | insert
 0x82 | num lock
 0x83 | scroll lock
 0x84 | left shift
 0x85 | right shift
 0x86 | left alt
 0x87 | right alt
 0x88 | left control
 0x89 | right control
 0x8a | left meta
 0x8b | right meta
 0x8c | reserved
 .... | reserved
 0x97 | reserved
 0x98 | unassigned
 .... | unassigned
 0x9f | unassigned
 0xa0 | F1
 0xa1 | F2
 0xa2 | F3
 0xa3 | F4
 0xa4 | F5
 0xa5 | F6
 0xa6 | F7
 0xa7 | F8
 0xa8 | F9
 0xa9 | F10
 0xaa | F11
 0xab | F12
 0xac | unassigned
 .... | unassigned
 0xaf | unassigned
 0xb0 | numpad 0
 0xb1 | numpad 1
 0xb2 | numpad 2
 0xb3 | numpad 3
 0xb4 | numpad 4
 0xb5 | numpad 5
 0xb6 | numpad 6
 0xb7 | numpad 7
 0xb8 | numpad 8
 0xb9 | numpad 9
 0xba | numpad *
 0xbb | numpad +
 0xbc | numpad Enter
 0xbd | numpad -
 0xbe | numpad .
 0xbf | numpad /
 0xc0 | unassigned
 0xc1 | delete
 0xc2 | home
 0xc3 | end
 0xc4 | page up
 0xc5 | page down
 0xc6 | up
 0xc7 | down
 0xc8 | left
 0xc9 | right
 0xca | escape
 0xcb | menu
 0xcc | pause
 0xcd | print screen
 0xce | unassigned
 .... | unassigned
 0xef | unassigned

table 2:

bit  0: left shift
bit  1: right shift
bit  2: caps lock
bit  3: insert
bit  4: num lock
bit  5: scroll lock
bit  6: left alt
bit  7: right alt
bit  8: left control
bit  9: right control
bit 10: left meta
bit 11: right meta

bits 12-23 are reserved for future versions. in this version, they should be set
to zero when giving a keycode, and should be ignored when recieving a keycode.