• 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:
    如何设置 ComboBox 下拉列表的高度或间距
    winform中ComboBox利用AutoComplete属性实现模糊查询(有缺陷)
    C#中combobox 控件属性、事件、方法
    ComboBox TextUpdate事件
    C#判断页面中的多个文本框输入值是否有重复的实现方法
    c# winfrom程序中 enter键关联button按钮
    WinForm 中ComboBox 绑定总结
    c# 实现ComboBox自动模糊匹配
    C#中ComboBox动态绑定赋值
    WinForm 中 comboBox控件之数据绑定
  • 原文地址:https://www.cnblogs.com/sky-heaven/p/9213923.html
Copyright © 2020-2023  润新知