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Using-the-Buttons.md

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The buttons on the EV3 are mapped as regular keyboard keys. UP, DOWN, LEFT, RIGHT, ENTER and BACKSPACE. The mapping on wheezy was UP, DOWN, LEFT, RIGHT, ENTER and ESC.

TODO: add photo.

Polling Key States

If you would rather poll the button states instead of using regular keyboard input methods, you can do that via the EVIOCGKEY ioctl on /dev/input/eventX. Key codes and ioctl definitions are in linux/input.h.

Here is an example using python:

#!/usr/bin/env python

import array
import fcntl
import sys

# from linux/input.h

KEY_UP = 103
KEY_DOWN = 108
KEY_LEFT = 105
KEY_RIGHT = 106
KEY_ENTER = 28
# KEY_ESC = 1      ## on wheezy
KEY_BACKSPACE = 14 ## on jessie

KEY_MAX = 0x2ff

def EVIOCGKEY(length):
    return 2 << (14+8+8) | length << (8+8) | ord('E') << 8 | 0x18

# end of stuff from linux/input.h

BUF_LEN = (KEY_MAX + 7) / 8

def test_bit(bit, bytes):
    # bit in bytes is 1 when released and 0 when pressed
    return not bool(bytes[bit / 8] & 1 << bit % 8)

def main():
    buf = array.array('B', [0] * BUF_LEN)
    with open('/dev/input/by-path/platform-gpio-keys.0-event', 'r') as fd:
        ret = fcntl.ioctl(fd, EVIOCGKEY(len(buf)), buf)

    if ret < 0:
        print "ioctl error", ret
        sys.exit(1)

    for key in ['UP', 'DOWN', 'LEFT', 'RIGHT', 'ENTER', 'BACKSPACE']:
        key_code = globals()['KEY_' + key]
        key_state = test_bit(key_code, buf) and "pressed" or "released"
        print '%s:' % key, key_state

if __name__ == "__main__":
    main()

Directly Reading the Event Device

If you want your program to be event driven, you can read the /dev/input/by-path/platform-gpio-keys.0-event file. It will block until a key is pressed. The data is in 16 byte blocks. The first 8 bytes are the time stamp (2 unsigned 64-bit integers, seconds and microseconds), the next 2 bytes are the type (unsigned 16-bit integer), the next 2 bytes are the code (unsigned 16-bit integer) and the last 4 bytes are the value (unsigned 32-bit integer).

Here is an example. It prints out 2 lines each time you press a button on the EV3 and 2 more lines each time you release a button. And of course, press CTRL+C to end.

root@ev3dev:/sys/class/leds# hexdump -e '"timestamp:%d.%6d""\t""" 1/2 "type:%i""\t"""  1/2 "code:%3i""\t"""  "value:%d\n"' /dev/input/by-path/platform-gpio-keys.0-event
timestamp:1411233011.710843     type:1  code: 14        value:0
timestamp:1411233011.710843     type:0  code:  0        value:0
timestamp:1411233011.930731     type:1  code: 14        value:1
timestamp:1411233011.930731     type:0  code:  0        value:0
timestamp:1411233018.910730     type:1  code:103        value:0
timestamp:1411233018.910730     type:0  code:  0        value:0
timestamp:1411233019.110728     type:1  code:103        value:1
timestamp:1411233019.110728     type:0  code:  0        value:0
timestamp:1411233027. 40849     type:1  code:108        value:0
timestamp:1411233027. 40849     type:0  code:  0        value:0
timestamp:1411233027.260726     type:1  code:108        value:1
timestamp:1411233027.260726     type:0  code:  0        value:0
timestamp:1411233029.280731     type:1  code: 28        value:0
timestamp:1411233029.280731     type:0  code:  0        value:0
timestamp:1411233029.450733     type:1  code: 28        value:1
timestamp:1411233029.450733     type:0  code:  0        value:0
timestamp:1411233032.770741     type:1  code:105        value:0
timestamp:1411233032.770741     type:0  code:  0        value:0
timestamp:1411233032.950844     type:1  code:105        value:1
timestamp:1411233032.950844     type:0  code:  0        value:0
timestamp:1411233035.800922     type:1  code:106        value:0
timestamp:1411233035.800922     type:0  code:  0        value:0
timestamp:1411233036. 20729     type:1  code:106        value:1
timestamp:1411233036. 20729     type:0  code:  0        value:0
^C