How to do things with the beaglebone

Beaglebone

Work with an EEPROM

cd /sys/bus/i2c/devices/i2c-2/
hexdump -C -v eeprom
echo 24c01 0x54 > /sys/bus/i2c/devices/i2c-2/new_device
-bash: echo: write error: Device or resource busy
dmesg tail -n 1:
  919.609895] i2c i2c-2: Failed to register i2c client 24c256 at 0x54 (-16)
echo 24c01 0x50 > /sys/bus/i2c/devices/i2c-2/new_device
dmesg:
[  933.505690] at24 2-0050: supply vcc not found, using dummy regulator
[  933.513194] at24 2-0050: 32768 byte 24c256 EEPROM, writable, 1 bytes/write
[  933.513451] i2c i2c-2: new_device: Instantiated device 24c256 at 0x50
root@BeagleBone:~# echo 24c01 0x50 > /sys/bus/i2c/devices/i2c-2/new_device

A few tips. 1) Make sure you have the write type of EEPROM. If you get the size wrong, it will not write correctly, and reading the eeprom file by sysfs will give garbage data. 2) i2cset and i2cset can be used, but only when you haven't instantiated a kernel driver. 3) There is an eeprom kernel module, an at24 kernel module (the one i used) and there is also flashrom (a program) which usually operates over SPI but also has parallel and i2c support.

dd to EEPROM

root@BeagleBone:~# dd if=image.png of=/sys/bus/i2c/devices/2-0050/eeprom count=128 bs=1
or
root@BeagleBone:~# echo "my text" | dd of=/sys/bus/i2c/devices/2-0050/eeprom count=7 bs=1 seek=10

dd is a good program to verify the eeprom is working correctly in sysfs. You can use either approach above, and verify with hexdump -C -v. Note the following: count must be used, or else you will likely get an error. With small eeproms (I have one that is 128 bytes) you can go over, (what I think) is the default of 512 bytes. If you have duplicate data in the eeprom (i.e. you write to it with /dev/zero you must use the -v flag in hexdump, otherwise it will omit duplicate data (rtfm).

• https://www.kernelconfig.io/config_eeprom_at24

Pocket Beagle

Output Text to TFT

This assumes you have the game boy tft shield. Although others that are supported and detected will likely work similarly.

echo "hello" > /dev/tty0

to output to your ssh session, try

echo "hello" > /dev/tty

These are serial output or char devices (as opposed to block which would be HDDs/flash (see a unix book)).

Access the char devices in /sys/dev/char These will be the same devices as in /dev but if you ls -l on /sys/dev/char you can get the path to the control / metadata of a given device. Such as you would expect to see when flashing a LED on/off via sys/fs. ref: https://elinux.org/EBC_Exercise_17_Switching_a_GPIO_to_an_LED#Setup and https://elinux.org/EBC_Exercise_17_Switching_a_GPIO_to_an_LED#Checking_.2Fsys.2Fclass.2Fleds

Going to /sys/dev/char is intuitive, and more so than /sys/class/whatever. But /sys/class has things that dev does not have, so you must remember /sys/dev/char and /sys/class for starters. This will get you access to hw control, afaik.

Output Video to TFT

Download video from somewhere. Resize/scale to small enough resolution (NOTE: this resolution is 128x96, from book Ffmpeg Basics by Korbel)

ffmpeg -i video.mp4 -s sqcif outputsmall.mp4
mplayer -loop 0 -vo fbdev2 outputsmall.mp4

Video should output direct on /dev/tty0

Framebuffer settings:

cd /sys
find . -print | grep fb0

There should be an fb0 (graphics) and fbcon (text console) e.g.

root@beaglebone:/sys/class/graphics# ls
fb0  fbcon

ref: https://unix.stackexchange.com/questions/342815/how-to-send-ffmpeg-output-to-framebuffer