EBC Exercise 12a 2.4 TFT LCD display via SPI
Embedded Linux Class by Mark A. Yoder
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.
Contents
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
Clone the course repo.
bone$ git clone https://github.com/MarkAYoder/BeagleBoard-exercises.git exercises
and then
bone$ cd exercises/display/ili9341 bone$ git pull bone$ cd tinyDRM bone$ ls BB-LCD-ADAFRUIT-24-SPI1-00A0.dts install.sh Makefile
BB-LCD-ADAFRUIT-24-SPI1-00A0.dts is the device driver for the LCD attached to SPI 1. It also assumes the backlight is attached to P9_14 (not P9_16 as in the table above.).
To compile it:
bone$ make cpp -x assembler-with-cpp -nostdinc -I /opt/source/dtb-4.19-ti/include -undef -D__DTS__ < BB-LCD-ADAFRUIT-24-SPI1-00A0.dts | dtc -i /opt/source/dtb-4.19-ti/include -I dts -O dtb -b 0 -o BB-LCD-ADAFRUIT-24-SPI1-00A0.dtbo - BB-LCD-ADAFRUIT-24-SPI1-00A0.dtbo: Warning (chosen_node_is_root): /fragment@0/__overlay__/chosen: chosen node must be at root nod bone$ make install sudo cp --backup BB-LCD-ADAFRUIT-24-SPI1-00A0.dtbo /lib/firmware Add uboot_overlay_addr4=/lib/firmware/BB-LCD-ADAFRUIT-24-SPI1-00A0.dtbo to /boot/uEnv.txt
Now, follow the instructions from the Makefile and 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
The 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
You can control the backlight with:
bone$ cd /sys/devices/platform/backlight_pwm/backlight/backlight_pwm bone$ sudo chgrp debian * bone$ sudo chmod g+w *
Turn the display off, then on with:
bone$ echo 1 > bl_power bone$ echo 0 > bl_power
Change the brightness to 25% with:
bone$ echo 25 > brightness
Now jump to the software section to see how to display images.
Legacy fbtft
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.
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$ 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
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
Embedded Linux Class by Mark A. Yoder