All my code was based upon an article from linuxjournal.com here is the article I based my code on
- C Read From Dev Input Event Center
- C Read From Dev Input Event Free
- How To Read /dev/input/event
- Linux Dev Input
Mar 13, 2017 Linux: Reading the Mouse events datas from /dev/input/mouse0 A simple program to check the /dev/input/mouse0 datas Tested on the raspberry PI with GPM installed. At this point you might wonder why I don't simply read the input event to read the keyboard input. This is because read is a blocking function. While ioctl is not blocking. If anyone could please help me figure out why EVIOCGKEY is returning the incorrect key values, I'd be very grateful.
I'm writing an embedded app, and I'm trying to read the keystrokes from a keyboard.
Here is the code I'm using
For the most part this code works, EXCEPT when I press 'a'.
According to the input.h KEY_A is set to be the value 30. But when I press 'a' on the keyboard, it returns the value 102 instead of 30. I've tested the other keys on the keyboard, and it seems like the keys 1-6 return the expected value of KEY_1, KEY_2 and etc., but after that the values returned aren't right.
I've tried reading the even directly from the /dev/input/eventX file. And the code returned in the events are expected.
The above code gives this print out when I hit the 'a' key. type 1 code 30 value 1
At this point you might wonder why I don't simply read the input event to read the keyboard input. This is because read() is a blocking function. While ioctl() is not blocking.
If anyone could please help me figure out why EVIOCGKEY() is returning the incorrect key values, I'd be very grateful. Thanks!
Ok, I figured out what the problem was.
my test_bit() macro was written incorrectly.
Basically, key_b[] represents the state of the keys, bit by bit. Meaning if KEY_A is pressed, then bit 30 will be set to 1. In this case, bit 30 will show up in key_b[3] as the value 0x40.
Here's a few more examples of how each key will map into key_b[].
- KEY_1 = 2 represented in key_b as --> key_b[0] = 0x04;
- KEY_2 = 3 represented in key_b as --> key_b[0] = 0x08;
- KEY_3 = 4 represented in key_b as --> key_b[0] = 0x10;
- KEY_4 = 5 represented in key_b as --> key_b[0] = 0x20;
- KEY_5 = 6 represented in key_b as --> key_b[0] = 0x40;
- KEY_6 = 7 represented in key_b as --> key_b[0] = 0x80;
- KEY_7 = 8 represented in key_b as --> key_b[1] = 0x01;
- KEY_8 = 9 represented in key_b as --> key_b[1] = 0x02;
- KEY_9 = 10 represented in key_b as --> key_b[2] = 0x04;
- KEY_0 = 11 represented in key_b as --> key_b[3] = 0x08;
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linux,bash,rhel
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python,linux,django,gcc,pip
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c,macros
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c,exec,ipc
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C Read From Dev Input Event Center
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c,pointers,dynamic-memory-allocation,behavior,realloc
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C Read From Dev Input Event Free
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How To Read /dev/input/event
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-->The ReadConsoleInput function can be used to directly access a console's input buffer. When a console is created, mouse input is enabled and window input is disabled. To ensure that the process receives all types of events, this example uses the SetConsoleMode function to enable window and mouse input. Then it goes into a loop that reads and handles 100 console input events. For example, the message 'Keyboard event' is displayed when the user presses a key and the message 'Mouse event' is displayed when the user interacts with the mouse.