• Explain EV in /proc/bus/input/devices data【转】


    转自:https://unix.stackexchange.com/questions/74903/explain-ev-in-proc-bus-input-devices-data

    It represent the bitmask for events supported by the device.
    
    Sample of 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
    
    The B in front stands for bitmap, N, P, S, U, H are simply first letter in corresponding name value and I is for ID. In ordered fashion:
    
        I => @id: id of the device (struct input_id)
            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.
    
    Bitmasks
    
    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.
    
    E.g.
    
    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 KEY bitmap.
    
    So, if we say:
    
    A = 0
    B = 1
    C = 6
    ...
    
    And then
    
    target = 0;
    set_bit(A, target);  => target ==      0001
    set_bit(C, target);  => target == 0100 0001
    
    Decoding 120013
    
    The value 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
    
    Then check 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.
  • 相关阅读:
    SQL Server常用到的几个设置选项
    动态加载母版页
    Sql查询技巧
    【WP7】关于磁贴的使用
    ashx,页面一般情况下不能方法session,必须添加两个接口。才能访问session。 狼
    悟头javascript学习笔记 狼
    IIS处理简介, IHttpHandler ,IHttpModel 狼
    在IIS下,不能执行exe文件解决办法。 狼
    给Ubuntu右键快捷菜单添加终端栏目
    VC 单文档程序 隐藏程序及任务栏图标
  • 原文地址:https://www.cnblogs.com/sky-heaven/p/9213923.html
Copyright © 2020-2023  润新知