Can anybody explain to me what the
EV value in
The keyboard always has value
Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems. It only takes a minute to sign up.Sign up to join this community
It represent the
bitmask for events supported by the device.
devices entry for a AT Keyboard:
I: Bus=0011 Vendor=0001 Product=0001 Version=ab41 N: Name="AT Translated Set 2 keyboard" P: Phys=isa0060/serio0/input0 S: Sysfs=/devices/platform/i8042/serio0/input/input2 U: Uniq= H: Handlers=sysrq kbd event2 B: PROP=0 B: EV=120013 B: KEY=20000 200 20 0 0 0 0 500f 2100002 3803078 f900d401 feffffdf ffefffff ffffffff fffffffe B: MSC=10 B: LED=7
B in front stands for
H are simply first letter in corresponding name value and
I is for
ID. In ordered fashion:
I => @id: id of the device
Bus => id.bustype
Vendor => id.vendor
Product => id.product
Version => id.version
N => name of the device.
P => physical path to the device in the system hierarchy.
S => sysfs path.
U => unique identification code for the device (if device has it).
H => list of input handles associated with the device.
B => bitmaps
PROP => device properties and quirks.
EV => types of events supported by the device.
KEY => keys/buttons this device has.
MSC => miscellaneous events supported by the device.
LED => leds present on the device.
As you know computers deal in binary, so:
1 = 0001 2 = 0010 3 = 0011 4 = 0100 5 = 0101 ...
So if i have a bitmap with value
5 that one would hold bits 0 and 2 in other
word one can give each number a name and check if they correspond to a value.
A = 1, 001 B = 2, 010 C = 4, 100
Then if I have
MYVAR = 5 which is
101 in binary this would check out:
MYVAR & A == TRUE (101 & 001 => 001) MYVAR & B == FALSE (101 & 010 => 000) MYVAR & C == TRUE (101 & 100 => 100 )
Thus my var has A and C.
The kernel uses a bit more sophisticated/complex way, and set bits by
offset. One reason being that more bits then is available in one computer (CPU) integer is used. For example look at the
So, if we say:
A = 0 B = 1 C = 6 ...
target = 0; set_bit(A, target); => target == 0001 set_bit(C, target); => target == 0100 0001
120013 is a hexadecimal. As binary it gives us:
0x120013 == 0001 0010 0000 0000 0001 0011 binary 1 2 0 0 1 3
Numbered from right they are:
2 1 <= offset (10's) 3210 9876 5432 1098 7654 3210 <= offset (counted from right) 0001 0010 0000 0000 0001 0011 <= binary Set bits are: 0, 1, 4, 17, 20
input.h you find that they correspond to:
0 EV_SYN (0x00) 1 EV_KEY (0x01) 4 EV_MSC (0x04) 17 EV_LED (0x11) 20 EV_REP (0x14)
To check what they mean a quick introduction is given by kernel Documentation.
* EV_SYN: - Used as markers to separate events. Events may be separated in time or in space, such as with the multitouch protocol. * EV_KEY: - Used to describe state changes of keyboards, buttons, or other key-like devices. * EV_MSC: - Used to describe miscellaneous input data that do not fit into other types. * EV_LED: - Used to turn LEDs on devices on and off. * EV_REP: - Used for autorepeating devices.
This, "EDIT 2 (continued):" in particular, might be of interest.