From 2dfbc312e6ccb88f838170d8e777d48aacde2ff5 Mon Sep 17 00:00:00 2001 From: johannst Date: Sun, 13 Nov 2022 14:13:35 +0000 Subject: deploy: 026d679006e5d470bacdc74bb3082072edf31e36 --- linux/input.html | 298 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 298 insertions(+) create mode 100644 linux/input.html (limited to 'linux/input.html') diff --git a/linux/input.html b/linux/input.html new file mode 100644 index 0000000..66eba36 --- /dev/null +++ b/linux/input.html @@ -0,0 +1,298 @@ + + + + + + input - Notes + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
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+

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

+ +
+ + +
+
+ + + +
+ + + + + + + + + + + + -- cgit v1.2.3