Revision needed - Embedded GUI Using Linux Frame Buffer Device with LVGL

[Uup115]

The tutorial is not compatible with 8.0. Noobs might have difficulty. I made several modifications to get it working.

https://blog.lvgl.io/2018-01-03/linux_fb

[sukesh-ak]

@Uup115 Can you share what you changed to make it working? I am in the same boat now. Using RPI OS Lite

[sukesh-ak]

Any help appreciated @kisvegabor @Uup115

Device/OS : Raspberry Pi with Desktop SDL version working fine - Display & Touch

Device/OS : Raspberry Pi Lite Display : Working Touch : Not working yet

Getting the following compiler error with touch is enabled using evdev

/usr/bin/ld: ./main.o: in function `main':
main.c:(.text.startup+0x74): undefined reference to `evdev_init'
/usr/bin/ld: main.c:(.text.startup+0x80): undefined reference to `evdev_read'
/usr/bin/ld: main.c:(.text.startup+0x90): undefined reference to `evdev_read'
collect2: error: ld returned 1 exit status
make: *** [Makefile:38: default] Error 1

Full Project is here for review https://github.com/sukesh-ak/LINUX-LVGL-FRAME-BUFFER

Code for touch here

[Uup115]

@Uup115 Can you share what you changed to make it working? I am in the same boat now. Using RPI OS Lite

The simplest route:

1. Start with the Linux port: https://github.com/lvgl/lv_port_linux_frame_buffer
2. Replace the two attached modified files: main.c and lv_conf.h ( modification(s) are below commented line(s))
3. Edit the file: /boot/config.txt and comment the line: vc4-fkms-v3d

You can edit the appropriate make files to shorten build time.

Embedded GUI Using Linux Frame Buffer Device with LVGL.tar.gz

[Uup115]

@sukesh-ak Looks like you're using the main repository for lvgl. I think it's best to clone from the Linux port: https://github.com/lvgl/lv_port_linux_frame_buffer

Kisvegabor already setup everything for Linux. You can edit the make files as needed.

[sukesh-ak]

@Uup115 thanks for your help.

My sample project is a clone of that project itself with few changes.

1. Local lv_drv_conf.h is still old which does not have the latest SDL (SDL display & touch works already now) and other updates from drivers folder. So the latest is copied from drivers repo.

2. I removed the demos since that repo is deprecated and have a label+2 buttons inside main.c for testing. Display works already.

I will check the attached files and revert soon.

[sukesh-ak]

@Uup115 Looks like the file you attached only has display and not touch. Like I mentioned above display is already working.

I need help to get touch working. Compiler error is when touch is enabled.

[kisvegabor]

I've have updated both the blog post and this rrepo.

It uses lvgl v8.2 (last release) but you can update to latest master without any issues.

[sukesh-ak]

Thank you @kisvegabor Will test and revert soon.

[Uup115]

@kisvegabor Thanks for the updates.

@sukesh-ak Run evtest to find where your touchscreen is mapped. In my case: /dev/input/event1. This needs to be set in file: "lv_drv_conf.h" @ line #397.
Be sure to #define USE_EVDEV 1 @ line #389.
In addition, I needed to #define EVDEV_CALIBRATE 1 @ line #400.

See attached "lv_drv_conf.h". lv_drv_conf.h.gz

[sukesh-ak]

Any idea why this could be happening with colors?

This happens if I use the instructions for Bullseye branch. Surprisingly, someone updated the Wiki page yesterday.

https://www.waveshare.com/wiki/2.8inch_DPI_LCD

[sukesh-ak]

@kisvegabor Thanks for the updates.

@sukesh-ak Run evtest to find where your touchscreen is mapped. In my case: /dev/input/event1. This needs to be set in file: "lv_drv_conf.h" @ line #397. Be sure to #define USE_EVDEV 1 @ line #389. In addition, I needed to #define EVDEV_CALIBRATE 1 @ line #400.

See attached "lv_drv_conf.h". lv_drv_conf.h.gz

Thank you @Uup115 Do you know why touch screen changes between event0 and event1 after reboot? How do I fix it?

[sukesh-ak]

Current status

evtest output

Available devices:
/dev/input/event0:      Goodix Capacitive TouchScreen

Display: working Touch: unable to open evdev interface:: No such file or directory

If I run like below, this error doesn't show up but touch doesn't work DISPLAY=:0 ./demo

If I run evtest, it detects touch so hardware is fine.

[Uup115]

Any idea why this could be happening with colors?

This happens if I use the instructions for Bullseye branch. Surprisingly, someone updated the Wiki page yesterday.

https://www.waveshare.com/wiki/2.8inch_DPI_LCD

As explained here: Edit the file: /boot/config.txt and comment the line which has: vc4-fkms-v3d

[sukesh-ak]

As explained here: Edit the file: /boot/config.txt and comment the line which has: vc4-fkms-v3d

I don't have the 'f'kms but have dtoverlay=vc4-kms-v3d as per Waveshare documentation. I have written to them as well and waiting.

With the new OS version (Raspberry Pi OS Bullseye branch) if I disable kms nothing shows up. It was a workaround for legacy version as I understand discussed here

[sukesh-ak]

Have now reverted to Raspberry Pi OS Buster branch now, so that display works as expected.

How do I rotate the touch? Tried enabling this but does not work.

# define EVDEV_SWAP_AXES 1 /*Swap the x and y axes of the touchscreen*/

[Uup115]

Have now reverted to Raspberry Pi OS Buster branch now, so that display works as expected.

How do I rotate the touch? Tried enabling this but does not work.

# define EVDEV_SWAP_AXES 1 /*Swap the x and y axes of the touchscreen*/

Maybe this (see comments):

#  define EVDEV_CALIBRATE         1   /*Scale and offset the touchscreen coordinates by using maximum and minimum values for each axis*/

#  if EVDEV_CALIBRATE
#    define EVDEV_HOR_MIN         0   /*to invert axis swap EVDEV_XXX_MIN by EVDEV_XXX_MAX*/
#    define EVDEV_HOR_MAX      4096   /*"evtest" Linux tool can help to get the correct calibraion values>*/
#    define EVDEV_VER_MIN         0
#    define EVDEV_VER_MAX      4096
#  endif  /*EVDEV_CALIBRATE*/

[sukesh-ak]

@Uup115 Yes I have already tried changing it. Its still won't swap. I also tried # define EVDEV_SWAP_AXES 1 /*Swap the x and y axes of the touchscreen*/

Reviewing this now https://github.com/lvgl/lv_drivers/blob/af07f57390ec50fb8cd2a52590141c2ab3ce6bee/indev/evdev.c#L112

Output of evtest. What should be the values of EVDEV_HOR_MIN etc?

  Event type 3 (EV_ABS)
    Event code 0 (ABS_X)
      Value      0
      Min        0
      Max      639
    Event code 1 (ABS_Y)
      Value      0
      Min        0
      Max      479
    Event code 47 (ABS_MT_SLOT)
      Value      0
      Min        0
      Max        4
    Event code 48 (ABS_MT_TOUCH_MAJOR)
      Value      0
      Min        0
      Max      255
    Event code 50 (ABS_MT_WIDTH_MAJOR)
      Value      0
      Min        0
      Max      255
    Event code 53 (ABS_MT_POSITION_X)
      Value      0
      Min        0
      Max      639
    Event code 54 (ABS_MT_POSITION_Y)
      Value      0
      Min        0
      Max      479
    Event code 57 (ABS_MT_TRACKING_ID)
      Value      0
      Min        0
      Max    65535

Btw, other than swapped X & Y, touch works

[Uup115]

@sukesh-ak Not sure. This is the output when I touch my screen:

Event: time 1648425830.433049, -------------- SYN_REPORT ------------
Event: time 1648425830.441088, type 3 (EV_ABS), code 53 (ABS_MT_POSITION_X), value 1836
Event: time 1648425830.441088, type 3 (EV_ABS), code 54 (ABS_MT_POSITION_Y), value 444
Event: time 1648425830.441088, type 3 (EV_ABS), code 60 (ABS_MT_TOOL_X), value 1836
Event: time 1648425830.441088, type 3 (EV_ABS), code 61 (ABS_MT_TOOL_Y), value 444
Event: time 1648425830.441088, type 3 (EV_ABS), code 0 (ABS_X), value 1836
Event: time 1648425830.441088, type 3 (EV_ABS), code 1 (ABS_Y), value 444
Event: time 1648425830.441088, type 4 (EV_MSC), code 5 (MSC_TIMESTAMP), value 1336100

[sukesh-ak]

@Uup115 Thanks for the details. I think there is an issue with hardware/driver itself. Not sure how this gets fixed in the RPI Desktop UI.

Scenario:

• OS: Raspberry Pi 64 Lite
• Default : Portrait with top on the side of USB/Ethernet
• No rotation applied in config
• No touch configured

When display is in portrait (default), X max should be 480 and Y max should be 640. Isn’t it? But as per output of evtest command, its switched. See below output

Output of evtest Available devices: /dev/input/event0: Goodix Capacitive TouchScreen Select the device event number [0-0]: 0

Input driver version is 1.0.1 Input device ID: bus 0x18 vendor 0x416 product 0x38f version 0x1060 Input device name: "Goodix Capacitive TouchScreen" Supported events: Event type 0 (EV_SYN) Event type 1 (EV_KEY) Event code 59 (KEY_F1) Event code 60 (KEY_F2) Event code 61 (KEY_F3) Event code 62 (KEY_F4) Event code 63 (KEY_F5) Event code 64 (KEY_F6) Event code 125 (KEY_LEFTMETA) Event code 330 (BTN_TOUCH) Event type 3 (EV_ABS) Event code 0 (ABS_X) Value 0 Min 0 Max 639 Event code 1 (ABS_Y) Value 0 Min 0 Max 479

I am working with Waveshare support to figure this out first.

[sukesh-ak]

This is how the touch cordinates from evtest looks like right now.

@kisvegabor Is this supposed to fix it? Because I tried and it does not work. A bug? # define EVDEV_SWAP_AXES 1 /*Swap the x and y axes of the touchscreen*/

[Uup115]

@sukesh-ak Touch resolution isn't necessarily equal to the resolution of the display. My display resolution is configured to 800x600. Per evtest, the touch resolution is higher. In my case, I use the following settings:

#  define EVDEV_CALIBRATE         1   /*Scale and offset the touchscreen coordinates by using maximum and minimum values for each axis*/

#  if EVDEV_CALIBRATE
#    define EVDEV_HOR_MIN         0   /*to invert axis swap EVDEV_XXX_MIN by EVDEV_XXX_MAX*/
#    define EVDEV_HOR_MAX      4096   /*"evtest" Linux tool can help to get the correct calibraion values>*/
#    define EVDEV_VER_MIN         0
#    define EVDEV_VER_MAX      4096
#  endif  /*EVDEV_CALIBRATE*/

[Uup115]

I think we can close this since the original issue has been resolved.