CODEWITHSUNDEEP
javalinuxeventshid
TameHog
TameHog

Reputation: 950

Java /dev/input/eventX

currently I have an N-Trig Multitouch panel hooked to the event file /dev/input/event4, and I am trying this to access it. I have included all of the natives and such in the java.library.path but am getting this error even when superuser. The exception:

java.io.IOException: Invalid argument
    at sun.nio.ch.FileDispatcherImpl.read0(Native Method)
    at sun.nio.ch.FileDispatcherImpl.read(FileDispatcherImpl.java:46)
    at sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:223)
    at sun.nio.ch.IOUtil.read(IOUtil.java:197)
    at sun.nio.ch.FileChannelImpl.read(FileChannelImpl.java:149)
    at com.dgis.input.evdev.EventDevice.readEvent(EventDevice.java:269)
    at com.dgis.input.evdev.EventDevice.access$1(EventDevice.java:265)
    at com.dgis.input.evdev.EventDevice$1.run(EventDevice.java:200)
EVENT:  null
Exception in thread "Thread-0" java.lang.NullPointerException
    at com.asdev.t3.Bootstrap$1.event(Bootstrap.java:41)
    at com.dgis.input.evdev.EventDevice.distributeEvent(EventDevice.java:256)
    at com.dgis.input.evdev.EventDevice.access$2(EventDevice.java:253)
    at com.dgis.input.evdev.EventDevice$1.run(EventDevice.java:201)

Does anyone know why this happens? Thanks

Upvotes: 1

Views: 1422

Answers (1)

LostParrot
LostParrot

Reputation: 41

I answered this question on the project's issues page.

by attilapara
Hi, I tried to use this library on a Raspberry Pi and I got the same exception, but I figured out the source of the problem and managed to get it work. Basically, the problem is that this library is written for 64 bit CPU/OS only. Explanation:

The input_event structure looks like this (source):

struct input_event {
    struct timeval time;
    unsigned short type;
    unsigned short code;
    unsigned int value;
};

Here we have timeval, which has the following members (source):

time_t         tv_sec      seconds
suseconds_t    tv_usec     microseconds

These two types are represented differently on a 32 bit and a 64 bit system.

The solution:

  1. Change the size of input_event from 24 to 16 bytes:

change line 34 of the source file evdev-java/src/com/dgis/input/evdev/InputEvent.java from this:

        public static final int STRUCT_SIZE_BYTES = 24;

to this:

        public static final int STRUCT_SIZE_BYTES = 16;

Change the parse function in the same source file as follows:

    public static InputEvent parse(ShortBuffer shortBuffer, String source) throws IOException {
        InputEvent e = new InputEvent();
        short a,b,c,d;
    
        a=shortBuffer.get();
        b=shortBuffer.get();
        //c=shortBuffer.get();
        //d=shortBuffer.get();
        e.time_sec = (b<<16) | a; //(d<<48) | (c<<32) | (b<<16) | a;
        a=shortBuffer.get();
        b=shortBuffer.get();
        //c=shortBuffer.get();
        //d=shortBuffer.get();
        e.time_usec = (b<<16) | a; //(d<<48) | (c<<32) | (b<<16) | a;
        e.type = shortBuffer.get();
        e.code = shortBuffer.get();
        c=shortBuffer.get();
        d=shortBuffer.get();
        e.value = (d<<16) | c;
        e.source = source;
    
        return e;
    }

Upvotes: 4

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