Linux input

Some notes on using /dev/input/* device driver files.

mouseX / mice

These device files are created by the [mousedev] driver.

/dev/input/mouseX represents the input stream for a SINGLE mouse device.
/dev/input/mice represents the merged input stream for ALL mouse devices.

The data stream consists of 3 bytes per event. An event is encoded as (BTN, X, Y).

BTN button pressed
X movement in x-direction -1 -> left and 1 -> right
Y movement in y-direction -1 -> down and 1 -> up

The raw data stream can be inspected as follows.

sudo cat /dev/input/mice | od -tx1 -w3 -v
+

eventX

These device files are created by the [evdev] driver.

/dev/input/eventX represents the generic input event interface a SINGLE input deivece.

Input events are encoded as given by the input_event struct below. Reading +from the eventX device file will always yield whole number of input events.

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

On most 64bit machines the raw data stream can be inspected as follows.

sudo cat /dev/input/event4 | od -tx1 -w24 -v
+

Identifyin device files.

To find out which device file is assigned to which input device the following +file /proc/bus/input/devices in the proc filesystem can be consulted.

This yields entries as follows and shows which Handlers are assigned to which +Name.

I: Bus=0018 Vendor=04f3 Product=0033 Version=0000
+N: Name="Elan Touchpad"
+...
+H: Handlers=event15 mouse0
+...
+

Example: Toying with `/dev/input/eventX`

Once compiled, the example should be run as sudo ./event /dev/input/eventX.

#include <stdio.h>
+#include <fcntl.h>
+#include <assert.h>
+#include <unistd.h>
+#include <time.h>
+
+#include <sys/time.h>
+#include <linux/input-event-codes.h>
+
+struct input_event {
+    struct timeval time;
+    unsigned short type;
+    unsigned short code;
+    unsigned int value;
+};
+
+const char* type(unsigned short t) {
+    static char buf[32];
+    const char* fmt = "0x%x";
+    switch (t) {
+#define FMT(TYPE) case TYPE: fmt = #TYPE"(0x%x)"; break
+        FMT(EV_SYN);
+        FMT(EV_KEY);
+        FMT(EV_REL);
+        FMT(EV_ABS);
+#undef FMT
+    }
+    snprintf(buf, sizeof(buf), fmt, t);
+    return buf;
+}
+
+const char* code(unsigned short c) {
+    static char buf[32];
+    const char* fmt = "0x%x";
+    switch (c) {
+#define FMT(CODE) case CODE: fmt = #CODE"(0x%x)"; break
+        FMT(BTN_LEFT);
+        FMT(BTN_RIGHT);
+        FMT(BTN_MIDDLE);
+        FMT(REL_X);
+        FMT(REL_Y);
+#undef FMT
+    }
+    snprintf(buf, sizeof(buf), fmt, c);
+    return buf;
+}
+
+const char* timefmt(const struct timeval* t) {
+    assert(t);
+    struct tm* lt = localtime(&t->tv_sec); // Returns pointer to static tm object.
+    static char buf[64];
+    strftime(buf, sizeof(buf), "%H:%M:%S", lt);
+    return buf;
+}
+
+int main(int argc, char* argv[]) {
+    assert(argc == 2);
+
+    int fd = open(argv[1], O_RDONLY);
+    assert(fd != -1);
+
+    struct input_event inp;
+    while (1) {
+        int ret = read(fd, &inp, sizeof(inp));
+        assert(ret == sizeof(inp));
+        printf("time: %s type: %s code: %s value: 0x%x\n",
+               timefmt(&inp.time), type(inp.type), code(inp.code), inp.value);
+    }
+}
+

[mousedev]: TODO /home/johannst/dev/linux/drivers/input/mousedev.c +[evdev]: TODO /home/johannst/dev/linux/drivers/input/evdev.c

+ +

Notes

Linux input

mouseX / mice

eventX

Identifyin device files.

Example: Toying with /dev/input/eventX

Example: Toying with `/dev/input/eventX`