Failure of python select.select() call on LibreElec

Hi,

I'm trying to create a Kodi addon that uses USB touchpanel input to make choices about what video to play.

I have python code that reads the touchpanel events and extracts raw x and y values.

To make it non-blocking, I use select.select() to first test to see if there is a touch event to read, and to set a timeout.

Everything works fine when I test it on Armbian, but when I embed the code into my Kodi addon, I never see any touchpanel events.

The program below represents my code.
On Armbian, the print (r) statement returns a data structure that points to the USB device file, whenever there is a touch event to read.

On LibreElec, the print [r] statement always returns []

Is there something stripped out of LibreElec that is making select.select not work right?

Note: from a python shell, "import select" succeeds, so I don't think it is a missing library.

Are there any other LibreElec restrictions that would inhibit a direct read of an input device?

Configuration:

Rock64 4GB

LibreELEC/Kodi (LibreELEC 9.1.002)

Confluence skin

Thanks,

-Jeff

#python touchscreen reader test
import os
import sys
import time
import struct
import select

#my touch panel
usbname = "/dev/input/by-id/usb-Touch_Touch_Device_FB60WH00D-CT-A1-10P-event-if00"	
EV_ABS=3         #I extracted this enum from a previous test
touch_timeout = 0.050

while True:
    if (os.access(usbname, os.R_OK)):
        fd=open(usbname, "rb")
        event=1  # force the while loop to start
        while event:  #as long as there is event data, keep reading
            r,w,e = select.select([fd], [], [],touch_timeout)
            print (r)
            if fd in r:
                event=os.read(fd.fileno(),EVENT_SIZE)
                (tv_sec, tv_usec, type, code, value) = struct.unpack(FORMAT, event)

                if (type == EV_ABS and code == 0 and value > 0):
                    rawX = value
                if (type == EV_ABS and code == 1 and value > 0):
                    rawY = value
            print("X " + str(rawX) + " Y " +str(rawY))
            else:   #else, there is no event data right now, so set event to jump out of loop
                event=0

    fd.close()

vpeter:

Great suggestion on testing select.select() with keyboard input. I wrote another test program (even simpler than before) to test this out, as well as testing with mouse and keyboard events.

I tested this, but failed for both keyboard and mouse events, too.

On Armbian, print (r) will correctly print out a data structure when I use the device, for touchpanel, keyboard, and mouse.

On LibreELEC, I only get a stream of [ ] printed out.

To reply to the other comments:

Whoops! I snipped out too much in my original example code when I was posting it. I used the following:

FORMAT = 'llHHI'
EVENT_SIZE = struct.calcsize(FORMAT)
But, the code never got to the read statement, due to the select.select() problem, so I didn't notice.

Interesting note about USB reliability vs. GPIO. Unfortunately I have 22 of these type of cheap touchpanels, and I can't change at this point. (This is for interactive displays at a charity haunted house)

import os
import select

#usbname = "/dev/input/by-id/usb-Logitech_USB_Receiver-event-kbd"    #keyboard
#usbname = "/dev/input/by-id/usb-Logitech_USB_Receiver-if01-event-mouse"    #mouse
usbname = "/dev/input/by-id/usb-Beijing_Qltouch_Tech_Co._LtD_USB_TouchScreen_QT-IRHS10-event-if02"

print (os.access(usbname, os.R_OK))
while True:
    if (os.access(usbname, os.R_OK)):
        fd=open(usbname, "rb")
        r,w,e = select.select([fd], [], [],0.1)
        print (r)
        fd.close()

Yes, this is running while Kodi is running. My plan was to use this for a Kodi addon to switch videos based on the location of the touch.

I tried to do an evtest test per vPeter's suggestion, but LibreELEC has blocked apt-get, so I can't install the package.

If Kodi on LibreELEC has really completely blocked access to input devices, it sounds like I'm out of luck using LibreELEC.
I'll try a clean install of Armbian and Kodi on my Rock64 and see how far I get.

It's a shame, I really liked how smoothly Kodi was running on LibreELEC.

vpeter:
Once again, some great suggestions.

Thanks for the pointer to system tools.

evtest does see the touchscreen and correctly identifies the touchscreen and properties.
But, it also notes that "The device is grabbed by another process". Which confirms your earlier assumption that Kodi grabs control of all IO. I guess that makes sense from a performance point of view.

Your code is a little difficult for me to digest all at once. I do see in the .sh script that you kill Kodi to launch the calibrate.py, and then restart Kodi.
This seems to confirm that Kodi runs with exclusive access to device input.

I'll have to research your suggestion to "create another input device in Python". I'm not sure how to do that, but I can look into it.

Your suggestion to run a background program with autostart interesting. I assume I could try to exclusively grab the input before Kodi starts (I don't need Kodi to have access to the touchpanel inputs).
I assume that the program would read the touchscreen events and send the data to my python addon (through a fifo pipe or file I/O?).
Is that what you had in mind?

Da Flex: interesting suggestion, but no, changing the "Enable mouse and touch screen support" setting has no effect.