new display driver in kernel 4.14.x

[dlech]

I just released a new ev3dev kernel on ev3dev-stretch that updates from 4.9.x to 4.14.x. This comes with a new display driver for the EV3 from the mainline kernel.

The new driver still provides a fbdev device (/dev/fb0) however, the memory layout is different. Because of limitations in the mainline kernel, there is no monochome. Instead it uses a 32-bit XRGB pixel format.

This causes an error with ev3dev-lang-python. See ev3dev/ev3dev#1022 (comment)

[dlech]

In reality, though, the display will now use 2-bit (4 color) grayscale 😮

[ddemidov]

So it looks like we should add a case for self.var_info.bits_per_pixel == 32 here with an appropriate encoder:

ev3dev-lang-python/ev3dev/core.py

Lines 3314 to 3319 in 55f57ad

	if self.var_info.bits_per_pixel == 1:
	self.mmap[:] = self._img.tobytes("raw", "1;IR")
	elif self.var_info.bits_per_pixel == 16:
	self.mmap[:] = self._img_to_rgb565_bytes()
	else:
	raise Exception("Not supported")

[ddemidov]

3b34f78 might help, but I did not have time to update to the 4.14 kernel and actually test it.

[ndward]

It's not clear to me whether the update() function in the 22 April Stretch image has been fixed. Is there something different I should be doing to be able to update the LCD? Should I expect a fix for this any time soon? Am I right in thinking that all the Stretch images released so far for the EV3 suffer either from the brickd hyperactivity bug or the update() function not working?

[dlech]

given the fact that this issue is still marked as open, I don't see why one would expect that it has been fixed.

in the meantime, if you want an older kernel with fixed brickd, I would suggest using an image older than 14 April and just upgrade the brickd package, but not the kernel (sudo apt update && sudo apt install brickd).

[ddemidov]

@ndward, you can help by testing if 3b34f78 works. You can do it by doing something like this in the EV3 command line:

git clone -b display-4.14 https://github.com/ev3dev/ev3dev-lang-python test-display-fix
cd ./test-display-fix
# test display by running some script from this directory,
# or interactively by opening python3

If you run any script while in test-display-fix directory, then this version of ev3dev should be picked up instead of the one installed system-wide.

[ndward]

I followed your instructions, then put this script in the test-display-fix folder (specifically, I used SFTP Net Drive to copy this script from another folder, which caused the copy to no longer be executable, so I then made it executable with chmod). Is it correct that I put the script directly in the test-display-fix folder and not in a subfolder?

#!/usr/bin/env python3
from ev3dev.ev3 import *
from time import sleep
lcd = Screen()
lcd.clear()
lcd.update()
sleep(5)

When I ran that script (right-click + Run in the EV3 browser) I got

Starting: brickrun --directory=/home/robot/test-display-fix /home/robot/test-display-fix/lcdtestshort.py
Started.
----------
Traceback (most recent call last):
  File "/home/robot/test-display-fix/lcdtestshort.py", line 6, in <module>
    lcd.update()
  File "/usr/lib/python3/dist-packages/ev3dev/core.py", line 3325, in update
    raise Exception("Not supported")
Exception: Not supported
----------
Exited with error code 1.

I got the same result using python3 interactively.

If the font is large in the above paragraph then that is not deliberate.

Image file:         ev3dev-stretch-ev3-generic-2018-04-22
Kernel version:     4.14.34-ev3dev-1.6.1-ev3
Brickman:           0.10.0
ev3devKit:          0.5.2
Board:              board0
BOARD_INFO_HW_REV=7
BOARD_INFO_MODEL=LEGO MINDSTORMS EV3
BOARD_INFO_ROM_REV=6
BOARD_INFO_SERIAL_NUM=00165340377E
BOARD_INFO_TYPE=main

[ddemidov]

The main module is now named ev3dev2 I think. Can you change the line

from ev3dev.ev3 import *

to

from ev3dev2.auto import *

?

[ddemidov]

Also, the Screen class is now called Display. There was some big restructuring recently in the stretch branch.

[ndward]

When I ran this script

#!/usr/bin/env python3
from ev3dev2.auto import *
from time import sleep
lcd = Display()
lcd.clear()
lcd.update()
sleep(5)

I got
Starting: brickrun --directory=/home/robot/test-display-fix /home/robot/test-display-fix/lcdtestshort.py

Started.
----------
Traceback (most recent call last):
  File "/home/robot/test-display-fix/lcdtestshort.py", line 6, in <module>
    lcd.update()
  File "/home/robot/test-display-fix/ev3dev2/display.py", line 290, in update
    self.mmap[:] = self._img_to_xrgb_bytes()
  File "/home/robot/test-display-fix/ev3dev2/display.py", line 277, in _img_to_xrgb_bytes
    return pack('H' * len(pixels), *pixels)
struct.error: ushort format requires 0 <= number <= (0x7fff * 2 + 1)
----------
Exited with error code 1.

Apart from Screen() becoming Display(), are there many other changes that need to be made in scripts? Is there a list of necessary changes somewhere?

[jabrena]

This is an important point, not only for Python library and users related. We should announce and track all changes to synchronize the changes or at least try. For Java, I will have to see how to solve the Display issue too, and it is complex. :(

[ddemidov]

@ndward, thanks for testing! I've pushed a fix that should address the problem. You can get it by doing git pull from inside test-display-fix directory. Can you try if that works?

[ddemidov]

The branch is yet to be released (this is a development branch). When that happens, I guess there will be a list of changes.