EBC Exercise 12a 2.4 TFT LCD display via SPI

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thumb‎ Embedded Linux Class by Mark A. Yoder


2.4" TFT LCD

This is an exercise in interfacing the 2.4" TFT LCD display (ili9341) via a SPI bus. The newer using the tinyDRM driver and the older uses fbtft.

The Hardware

This table shows how to wire the LCD display for SPI 0.

LCD Bone
MISO P9_21
LED P9_16
SCK P9_22
MOSI P9_18
D/C P9_19
RESET P9_20
CS P9_17
GND P9_2
VCC P9_4

tinyDRM

The tinyDRM driver requires a 4.19 kernel or newer. Run uname -a to see which kernel is being run. If it isn't new enough run:

bone$ cd /opt/scripts/tools
bone$ sudo ./update_kernel.sh --lts-4_19
bone$ reboot

Find the device trees:

bone$ cd /opt/source/bb.org-overlays
bone$ git pull
bone$ ls src/arm/BB-LCD*
src/arm/BB-LCD-ADAFRUIT-24-SPI0-00A0.dts src/arm/BB-LCD-ADAFRUIT-18-SPI1-00A0.dts   
src/arm/BB-LCD-ADAFRUIT-24-SPI1-00A0.dts

BB-LCD-ADAFRUIT-24-SPI1-00A0.dts is the device driver for the LCD attached to SPI 1.

Compile it via Makefile. All the devices trees will be compiled.

bone$ make
...
  DTC     src/arm/BEAGLEBOY-0013.dtbo
  DTC     src/arm/BB-LCD-ADAFRUIT-24-SPI1-00A0.dtbo
  DTC     src/arm/PB-USB0-HOST.dtbo
...
bone$ sudo cp src/arm/BB-LCD-ADAFRUIT-24-SPI1-00A0.dt /lib/firmware/

Add uboot_overlay_addr4=/lib/firmware/BB-LCD-ADAFRUIT-24-SPI1-00A0.dtbo to /boot/uEnv.txt

Now edit /boot/uEnv.txt and find the line starting with

#uboot_overlay_addr4=/lib/firmware

Uncomment it and change it to:

uboot_overlay_addr4=/lib/firmware/BB-LCD-ADAFRUIT-24-SPI1-00A0.dtbo

Then reboot and check of /dev/fb0

bone$ sudo reboot

After rebooting...

bone$ ls -ls /dev/fb0
0 crw-rw---- 1 root video 29, 0 Oct  3 10:07 /dev/fb0

The LCD should be showing some text.

You can control the backlight with:

bone$ cd /sys/class/backlight/backlight_pwm

Turn the display off, then on with: (Yup, it's backwards.)

bone$ echo 1 > bl_power                        
bone$ echo 0 > bl_power

Change the brightness to 25% with:

bone$ echo 25 > brightness

Now jump to the Using the Frame Buffer section to see how to display images, etc..

Using the framebuffer

Displaying Images

Follow the instructions in install.sh to download fbi and some images.

bone$ sudo apt update
bone$ sudo apt install fbi

Display them with:

bone$ sudo fbi -noverbose -T 1 -a boris.png

You should now see Boris the Beagle on your display.

Playing Movies

Install mplayer and load a movie on the Bone (see install.sh).

bone$ sudo apt install mplayer

Get something to play

bone$ wget http://hubblesource.stsci.edu/sources/video/clips/details/images/hst_1.mpg

And play it

bone$ mplayer -vo fbdev2 -nolirc -framedrop hst_1.mpg

If you get an error you might need:

bone$ export SDL_VIDEODRIVER=fbcon 
bone$ export SDL_FBDEV=/dev/fb0

Play the movie. Rotate the movie.

Generate Text

Install imagemagick.

bone$ sudo apt install imagemagick

See text.sh for an example of using imagemagick to write text to the LCD display. Write your name on the LCD. Display an image and write some text on it.

# Here's how to use imagemagick to display text
# Make a blank image
SIZE=320x240
TMP_FILE=/tmp/frame.png

# From: http://www.imagemagick.org/Usage/text/
convert -background lightblue -fill blue -font Times-Roman -pointsize 24 \
     -size $SIZE \
     label:'ImageMagick\nExamples\nby Anthony' \
     -draw "text 0,200 'Bottom of Display'" \
     $TMP_FILE

sudo fbi -noverbose -T 1 $TMP_FILE

pygame

It's not hard to get pygame to display on the LCD.

bone$ sudo apt install pygame
bone$ sudo pip3 install requests pillow
bone$ cd exercises/displays/ili9341/fb/pygame
bone$ sudo ./clock.py

Look in clock.py to see how to direct the graphics to the LCD.

fbtft

fbtft is no longer supported after the 5.4 kernel. (https://github.com/notro/fbtft/wiki#fbtft_device-and-flexfb-are-gone-in-54)

Clone the course repo.

bone$ git clone https://github.com/MarkAYoder/BeagleBoard-exercises.git exercises

and then

bone$ cd exercises/display/ili9341/fb
bone$ git pull
bone$ ./on.sh

After a moment the display should turn dark. Look in on.sh to see what it did. If the display doesn't turn on, look in on.sh and make sure it's set for the correct SPI bus.




thumb‎ Embedded Linux Class by Mark A. Yoder