Zephyr + nRF5240 DK + lvgl + SSD1306

[Carlos Galiana]

Hi,

I am developing an application with the lvgl driver. I was trying to make the example lvgl works, but I can not. I am using a 128 x 32 screen with a ssd1306 controller (in the description of the example says it is compatible). When I connect the screen to the board and flash the code nothing happens (the screen does not turn on). I dont know what part of the configuration I have to change depending on the screen type. I connect the screen to 5V and GND of the DK and the I2C to 31 and 30 pins. I did not change noting in the code. Doing debug of the code I have seen that the the functions below the "device_get_binding" does not execute. 

¿Do you know if I am missing something important about the configuration?. I think the problem is the configuration of the display in the kconfig or the configuration in the I2C bus. ¿Am I in the way?. I can not see where it is exactly.

#include <device.h>
#include <drivers/display.h>
#include <lvgl.h>
#include <stdio.h>
#include <string.h>
#include <zephyr.h>

#define LOG_LEVEL CONFIG_LOG_DEFAULT_LEVEL
#include <logging/log.h>
LOG_MODULE_REGISTER(app);

void main(void)
{
	uint32_t count = 0U;
	char count_str[11] = {0};
	const struct device *display_dev;
	lv_obj_t *hello_world_label;
	lv_obj_t *count_label;

	display_dev = device_get_binding(CONFIG_LVGL_DISPLAY_DEV_NAME);

	if (display_dev == NULL) {
		return;
	}

	if (IS_ENABLED(CONFIG_LVGL_POINTER_KSCAN)) {
		lv_obj_t *hello_world_button;

		hello_world_button = lv_btn_create(lv_scr_act(), NULL);
		lv_obj_align(hello_world_button, NULL, LV_ALIGN_CENTER, 0, 0);
		lv_btn_set_fit(hello_world_button, LV_FIT_TIGHT);
		hello_world_label = lv_label_create(hello_world_button, NULL);
	} else {
		hello_world_label = lv_label_create(lv_scr_act(), NULL);
	}

	lv_label_set_text(hello_world_label, "Hello world!");
	lv_obj_align(hello_world_label, NULL, LV_ALIGN_CENTER, 0, 0);

	count_label = lv_label_create(lv_scr_act(), NULL);
	lv_obj_align(count_label, NULL, LV_ALIGN_IN_BOTTOM_MID, 0, 0);

	lv_task_handler();
	display_blanking_off(display_dev);

	while (1) {
		if ((count % 100) == 0U) {
			sprintf(count_str, "%d", count/100U);
			lv_label_set_text(count_label, count_str);
		}
		lv_task_handler();
		k_sleep(K_MSEC(10));
		++count;
	}
}

I have added the shield in CMakeList

# SPDX-License-Identifier: Apache-2.0

cmake_minimum_required(VERSION 3.20.0)

find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(lvgl)

FILE(GLOB app_sources src/*.c)
target_sources(app PRIVATE ${app_sources})
set(ssd1306_128x32)

Thanks for your time 

[Simon]

It seems like you're using the sample \zephyr\samples\subsys\display\lvgl

• The display_dev struct, which is returned from device_get_binding(CONFIG_LVGL_DISPLAY_DEV_NAME) is passed into display_blanking_off()
• The display_blanking_off() function is part of the API zephyr/include/drivers/display.h
• The API functions display.h, has to be linked with one of the source files in zephyr/drivers/display, and I think it is the file zephyr/drivers/display/ssd1306.c in your case
  • You can see that blanking_off() will be linked to ssd1306_resume()
• To enable the driver ssd1306.c, you need to do the following
  
  • Set the Kconfig CONFIG_SSD1306 in the prj.conf
    • See https://github.com/nrfconnect/sdk-zephyr/blob/2fb8ab3509edf39bd8f420e1fc57632dd561b5ac/drivers/display/CMakeLists.txt#L16
  • Enable a node in the device tree with the compatible "solomon,ssd1306fb"
    • See https://github.com/nrfconnect/sdk-zephyr/blob/2fb8ab3509edf39bd8f420e1fc57632dd561b5ac/drivers/display/ssd1306.c#L7 
    • Take a look at these to see how you can go about this:
      • https://github.com/nrfconnect/sdk-zephyr/blob/2fb8ab3509edf39bd8f420e1fc57632dd561b5ac/boards/shields/ssd1306/ssd1306_128x32.overlay#L17 
    • This guide might give you some clues how to go about this as well: https://devzone.nordicsemi.com/guides/nrf-connect-sdk-guides/b/peripherals/posts/lvgl-on-a-tft-lcd-display-with-the-nrf9160-dk 
• You also need to set CONFIG_LVGL_DISPLAY_DEV_NAME to the same value as the label you pass into the "solomon,ssd1306fb" node, so try setting CONFIG_LVGL_DISPLAY_DEV_NAME="SSD1306" in the prj.conf file
• Lastly you need to make the init function in ssd1306.c runs successfully, if not the call to device_get_binding() will fail
  • The init function runs here, and if it fails it will set this, which will make device_binding fail
  • As you can see, the function ssd1306_init() is passed into the device define macro
  • The init function will check if the device is connected and works correctly, through a lot of commands
  • When ssd1306_init() runs, make sure to connect the display correctly to the chip, you need to connect it according to how you have configured the hardware in the device tree. For example if you've placed the "solomon,ssd1306fb" node inside i2c0, use the pins i2c0 is configured with (to figure out this, open sample/build/zephyr/zephyr.dts and search for i2c0). Check out the Thingy board dts file to see how to change i2c configurations: https://github.com/nrfconnect/sdk-nrf/blob/3d51870a11dbbdab8558d9d77f71057e5ef5893d/boards/arm/thingy91_nrf9160/thingy91_nrf9160_common.dts#L113-L118 

If anything is unclear, or if you face any more difficulties following my instructions, don't hesitate to ask

Best regards,

Simon

[sipan112]

This requires some knowledge about the build-configuration process for zephyr.

The difficult part are setting up the I2C driver for the target board. In this project, the nRF52 I2C support is well-known and relatively straightforward in configuring. Other SOCs and boards are not always so easy.

[Carlos Galiana]

Hi Simon. Thanks for the time you have spent answering me. The lvgl guide from Zephyr says that you have to use the Shield of ssd1306 (called "ssd1306_128x32" in my case) from the SDK. This shield includes a kconfig.defconfig file which put the display name as "SSD1306" and execute "config SSD1306". The shield also has an overlay file creating a node with the requirements and the links you have commented. I have set the shield in the CMakeList.txt as follows:

cmake_minimum_required(VERSION 3.20.0)

find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(lvgl)

FILE(GLOB app_sources src/*.c)
target_sources(app PRIVATE ${app_sources})
set(SHIELD ssd1306_128x32)

The shield contents the following files

• The kconfig.defconfig form the shield file set:

if SHIELD_SSD1306_128X64 || SHIELD_SSD1306_128X32 || SHIELD_SH1106_128X64

config I2C
	default y

endif # SHIELD_SSD1306_128X64 || SHIELD_SSD1306_128X32 || SHIELD_SH1106_128X64

config SSD1306
	default y

choice SSD1306_CONTROLLER_TYPE
	default SSD1306_SH1106_COMPATIBLE if SHIELD_SH1106_128X64
endchoice

if LVGL

config LVGL_DISPLAY_DEV_NAME
	default "SSD1306"

• The overlay file from the shield:

&arduino_i2c {
	status = "okay";

	ssd1306@3c {
		compatible = "solomon,ssd1306fb";
		reg = <0x3c>;
		label = "SSD1306";
		width = <128>;
		height = <32>;
		segment-offset = <0>;
		page-offset = <0>;
		display-offset = <0>;
		multiplex-ratio = <31>;
		segment-remap;
		com-invdir;
		com-sequential;
		prechargep = <0x22>;
	};
};

The DeviceTree of my board nrf52840dk_nrf52840.dts.pre.tmp file:

  i2c0: i2c@40003000 {
   #address-cells = <1>;
   #size-cells = <0>;
   reg = <0x40003000 0x1000>;
   clock-frequency = <100000>;
   interrupts = <3 1>;
   status = "disabled";
   label = "I2C_0";
  };

arduino_i2c: &i2c0 {
 compatible = "nordic,nrf-twi";
 status = "okay";
 sda-pin = <26>;
 scl-pin = <27>;
};

Although I set the shield the way I have showed you the autoconfig.h is not taking the changes.

Do you know what could be going on?

When I try to set "CONFIG SDD1306=y " in the proj.conf (I know the shield do it for me but as I said, it was not working) this warning occurs:

I have realised that if I go to the kconfig GUI from VisualStudio you have the option of enable SDD1306 driver, but I cant selct the option (I dont know why).

Again, thank you for your time. Your message has guided me a lot.

[Carlos Galiana]

Thank you sipan112. I am trying to learnt as fast as possible, but like you said, I select nrf52840 because the amount of examples around it.

[Carlos Galiana]

It is solved. I was missing CONFIG_I2C=y in prj.confg.

Thank you Simon!