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Input events

Users can interact with a computer using various input devices : the most obvious are keyboards, mice and joysticks ... but it exists others like intrusion detectors for desktops or servers, dedicated keys or proximity detectors on tablet and so one and so forth.
The Linux kernel exposes raw events of such devices to userspace through a collection of character device nodes : the event interface.
SelEvent is the easiest way Séléné applications can manage such information.

Input events are exposed in /dev/input directory. For example, on an average MID-A10 tablet

laurent@Tablette ~ $ ls /dev/input/
by-path  event0  event1  mice

mice is the touchscreen exposed as a mice (unfortunately, it doesn't work due to lacks of proper drive,r but it's another story).
But what are event0 and event1 ? Let's have a look in /proc/bus/input/devices

laurent@Tablette ~ $ cat /proc/bus/input/device
I: Bus=0019 Vendor=0001 Product=0001 Version=0100
N: Name="axp20-supplyer"
P: Phys=m1kbd/input2
S: Sysfs=/devices/platform/sunxi-i2c.0/i2c-0/0-0034/axp20-supplyer.28/input/input0
U: Uniq=
H: Handlers=kbd event0
B: PROP=0
B: EV=7
B: KEY=100000 0 0 0
B: REL=0

I: Bus=0019 Vendor=0001 Product=0001 Version=0100
N: Name="sun4i-keyboard"
P: Phys=sun4ikbd/input0
S: Sysfs=/devices/virtual/input/input1
U: Uniq=
H: Handlers=kbd event1
B: PROP=0
B: EV=3
B: KEY=2000000 0 800 c0040 0 0 10000002

The field N indicates which is the driver for this device, so, by extension the signals we can git from it (not something that can be invented). In the example above, "axp20-supplyer" is the driver managing the power supply, consequently, we will here "POWER" key status. "sun4i-keyboard" is for tablet additional keys like VolumeUp, VolumeDown and such. Sometime, this field is more explicit, like 'ImPS/2 Generic wheel mouse".
Field H indicates which kind of messages we will receive ( kbd for keyboard here ), and to which event it is connected (event0).

Selene example

The full source code can be found here.

The 1st step is to create the event

evt = SelEvent.create('/dev/input/event1', rcv_event)

and the corresponding callback function

function rcv_event()
        print('event received')
        local t, tp, c, v = evt:read()
        print( os.date('%c', t), tp, SelEvent.TypeName(tp), c, SelEvent.KeyName(c), v)
end

evt:read() method will read one by one waiting events and returns

All codes can be found in file /usr/include/linux/input.h with EV_ prefixe for types and KEY_ for ... keys.

Finally, a classical WaitFor() loop with our SelEvent as argument.

while true do
local rt = table.pack( Selene.WaitFor(evt) )
for _,ret in ipairs(rt) do
if type(ret) == 'function' then
ret()
end
end
end

More than 1 "input event" to listen ?

Not an issue :

As example :

evt0 = SelEvent.create('/dev/input/event0', handlekeys0)
evt1 = SelEvent.create('/dev/input/event1', handlekeys1)

then

while true do
local rt = table.pack( Selene.WaitFor(evt0,evt1) )
for _,ret in ipairs(rt) do
if type(ret) == 'function' then
ret()
end
end
end

Notez-bien : as the callback function as no way to know with SelEvent it has to deal with, you need to create as many callbacks as you have input events.

Various notes about input events


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