Re: writing a keyboard driver

[James S. <jsi...@su...>]

> I am just sitting down to write a kernel module for an Apple Newton serial
> keyboard,a nd I am slightly confused by the terminology about scancodes.
> 
> 1.7 The keycode, keycodemax, keycodesize fields
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> These two fields will be used for any inpur devices that report their data
> as scancodes. If not all scancodes can be known by autodetection, they may
> need to be set by userland utilities. The keycode array then is an array
> used to map from scancodes to input system keycodes. The keycode max will
> contain the size of the array and keycodesize the size of each entry in it
> (in bytes).

Scancodes are what are generated by the hardware. If you press a 7 on
say a alpha you might get a code from hardware of say 34. On a PC you
get a value of 117. The input system has a bunch of defined values for
specific keys. So if you are reading /dev/eventX and you get KEY_7 this
means you press a 7 no matter what the value was the hardware generated. 
Each input driver has a keycode array to perform this mapping which
basically goes from hardware specific codes to universal
codes. keycode_max is the size of the array which is the maximum number of 
keys that can generate codes times what the size of the each field 
(keycodesize).