Exploring the Chips

Understanding the /sys/bus/i2c/devices/ Directory on the BeagleBoard

The BeagleBoard, like other Linux-based embedded systems, utilizes the sysfs interface to provide a standardized way to interact with hardware components, such as I2C devices. The directory /sys/bus/i2c/devices/ is specifically related to the I2C (Inter-Integrated Circuit) bus, which is commonly used for connecting low-speed peripherals to the main board's processor.

1. What is I2C?

I2C is a synchronous, multi-master, multi-slave, packet-switched, single-ended, serial communication bus. It's widely used for attaching lower-speed peripheral ICs to processors and microcontrollers in short-distance, intra-board communication.

2. Structure of /sys/bus/i2c/devices/

The /sys/bus/i2c/devices/ directory in Linux contains a list of all the I2C devices currently recognized by the system. This directory is dynamically populated by the kernel when it detects devices on the I2C buses.

Each entry in this directory follows a naming convention based on the bus number and the device address:

i2c-<bus number>-<device address>

i2c-1-0050

3. Interacting with I2C Devices

To interact with I2C devices through /sys/bus/i2c/devices/, you need to understand the basic components provided in this directory for each device.

Example Structure for an I2C Device

Within each device directory (e.g., /sys/bus/i2c/devices/i2c-1-0050/), you'll find several files and subdirectories, such as:

• name: This file contains the name of the I2C device.
• modalias: This file contains the modalias of the device, used by the kernel to load the appropriate driver.
• subsystem: This symlink points to the subsystem (i2c in this case) under which this device is categorized.
• uevent: This file contains attributes that the kernel sends to udev when the device is added or removed.
• driver: A symlink to the device's driver if it's bound to one.
• power: A directory that contains power management information for the device.

4. Common Tasks

1. Listing I2C Devices:
   You can list all I2C devices connected to the BeagleBoard using the following command:

   Terminal

   ls /sys/bus/i2c/devices/
   

   This command will output all detected I2C devices with their respective bus numbers and addresses.

2. Interpreting the I2C Devices Listed in /sys/bus/i2c/devices/ on the BeagleBoard

   You ran the following command to list all I2C devices on the BeagleBoard:

   Terminal

   tail -v -n +1 /sys/bus/i2c/devices/*/name
   

   Output

   ==> /sys/bus/i2c/devices/0-0024/name <==
   tps65217
   
   ==> /sys/bus/i2c/devices/0-004c/name <==
   it66122
   
   ==> /sys/bus/i2c/devices/0-0050/name <==
   24c256
   
   ==> /sys/bus/i2c/devices/2-0054/name <==
   24c256
   
   ==> /sys/bus/i2c/devices/2-0055/name <==
   24c256
   
   ==> /sys/bus/i2c/devices/2-0056/name <==
   24c256
   
   ==> /sys/bus/i2c/devices/2-0057/name <==
   24c256
   
   ==> /sys/bus/i2c/devices/i2c-0/name <==
   OMAP I2C adapter
   
   ==> /sys/bus/i2c/devices/i2c-2/name <==
   OMAP I2C adapter
   

• Explanation of Each Device:

  Below is the breakdown of each entry in the output:

  • /sys/bus/i2c/devices/0-0024/name

    • Device Address: 0x24 (hexadecimal)
    • Bus Number: 0
    • Device Name: tps65217
    • Description: The power management IC (PMIC) commonly used to manage power supplies.
    • Datasheet: https://www.ti.com/lit/ds/symlink/tps65217.pdf

  • /sys/bus/i2c/devices/0-004c/name

    • Device Address: 0x34 (hexadecimal)
    • Bus Number: 0
    • Device Name: it66122
    • Description: An HDMI CEC (Consumer Electronics Control) controller, often used in devices that support HDMI connections.
    • Datasheet: https://github.com/hd-zero/hdzero-goggle/blob/main/docs/IT66121FN_Datasheet.pdf

  • /sys/bus/i2c/devices/0-0050/name

    • Device Address: 0x50 (hexadecimal)
    • Bus Number: 0
    • Device Name: 24c256
    • Description: refers to an EEPROM (Electrically Erasable Programmable Read-Only Memory) chip with a capacity of 16GB.
    • Datasheet: https://www.mouser.com/catalog/specsheets/Kingston_03-19-2025_5625_EMMC16G-MW28-03010.pdf

  • /sys/bus/i2c/devices/0-0070/name

    • Device Address: 0x70 (hexadecimal)
    • Bus Number: 0
    • Device Name: tda998x
    • Description: tda998x is an HDMI transmitter controller used to convert video signals for HDMI output.

  • /sys/bus/i2c/devices/2-0054/name to /sys/bus/i2c/devices/2-0057/name

    • Device Addresses: 0x54, 0x55, 0x56, 0x57 (hexadecimal)
    • Bus Number: 2
    • Device Name: 24c256
    • Description: These are additional EEPROM chips, possibly different banks or sections of memory, all sharing the same I2C bus but with different addresses.

  • /sys/bus/i2c/devices/i2c-0/name, /sys/bus/i2c/devices/i2c-1/name, /sys/bus/i2c/devices/i2c-2/name

    • Device Names: OMAP I2C adapter
    • Description: These entries represent the I2C bus adapters themselves, not specific I2C devices. OMAP I2C adapter refers to the I2C controller on the OMAP processor used in BeagleBoard systems. There are three separate I2C buses (i2c-0, i2c-1, and i2c-2).

5. Installing i2c-tools

3. Using the your host machine, download the following file from GitHub oudream/i2c-tools

   • https://github.com/oudream/i2c-tools/archive/refs/tags/v4.3.zip

4. Using the termnial open another tab or instance and using secure copy (scp) lets send the file to the BeagleBone

   Terminal

   scp Downloads/i2c-tools-master.zip debian@192.168.7.2:
   Debian GNU/Linux 12
   
   BeagleBoard.org Debian Bookworm Base Image 2025-05-27
   Support: https://bbb.io/debian
   default username is [debian] with a one time password of [temppwd]
   
   debian@192.168.7.2's password:
   i2c-tools-master.zip                                                                  100%  128KB   2.5MB/s   00:00
   

5. Navigate back the ssh session and you should see the following:

   Terminal

   ls
   

   Output

   i2c-tools-master.zip
   

6. unzip the folder

   Terminal

   unzip i2c-tools-master.zip
   

   Output

   Archive:  i2c-tools-master.zip
   ccf4c4ce924acc847b2e49bfc749a723f68ba75a
      creating: i2c-tools-master/
     inflating: i2c-tools-master/.gitignore
     inflating: i2c-tools-master/CHANGES
     inflating: i2c-tools-master/COPYING
     inflating: i2c-tools-master/COPYING.LGPL
     inflating: i2c-tools-master/Makefile
     inflating: i2c-tools-master/README
   ...
   extracting: i2c-tools-master/version.h
   

7. Next we are going to install the tool

   Terminal

   cd i2c-tools-master/
   sudo make install && cd
   

   Output

   cc -fpic -D_REENTRANT -O2 -Wall -Wstrict-prototypes -Wshadow -Wpointer-arith -Wcast-qual -Wcast-align -Wwrite-strings -Wnested-externs -Winline -W -Wundef -Wmissing-prototypes -Iinclude -c lib/smbus.c -o lib/smbus.o
   cc -shared  -Wl,--version-script=lib/libi2c.map -Wl,-soname,libi2c.so.0 -o lib/libi2c.so.0.1.1 lib/smbus.o -lc
   cc -O2 -Wall -Wstrict-prototypes -Wshadow -Wpointer-arith -Wcast-qual -Wcast-align -Wwrite-strings -Wnested-externs -Winline -W -Wundef -Wmissing-prototypes -Iinclude -c lib/smbus.c -o lib/smbus.ao
   rm -f lib/libi2c.a
   ...
   install -m 755 -d /usr/local/include/i2c
   for file in i2c/smbus.h ; do \
   install -m 644 include/$file /usr/local/include/$file ; done
   ...
   install -m 755 tools/$program /usr/local/sbin ; \
   install -m 644 tools/$program.8 /usr/local/share/man/man8 ; done
   

8. Export /usr/sbin so that is part of our PATH

   Terminal

   echo -e "export PATH=\$PATH:/usr/sbin" >> .bashrc
   

   Note

   You will need to re-source the .bashrc to reload the configuration for the current shell

   source .basrhc
   

9. Verify install:

   Terminal

   command -v i2cdump
   

   Output

   /usr/sbin/i2cdump
   

10. Clean up, remove the i2cdump download

rm -rf i2c-tools-master*

6. Next Steps

11. Computer says no...

You want to read the registers of the tps65217 power management IC on your BeagleBoard using i2cdump. However, you may encounter the error:

i2cdump -y 0 0x24 
Error: Could not set address to 0x24: Device or resource busy

12. Using i2cdump to Read the Registers

We can force a look into the register by using -f to bypass the "in use by driver" check

Run following command:

sudo i2cdump -f -y 0 0x24 b

This command will provide a hex dump of all the registers in the tps65217 device in byte (b) format.

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: e2 3f 20 01 b1 80 b2 01 00 00 84 00 7f 0c 18 11    ?? ?????..?.????
10: 08 06 09 38 26 3f 7f 00 03 15 5f 32 40 20 00 00    ???8&??.??_2@ ..
20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................

13. Explaining the i2cdump Output

The i2cdump output shows the register values of the tps65217 device. Let's interpret the first few lines:

• 0x00 to 0x0F: General configuration and status registers.

  • 0x00 (e2): A possible configuration register controlling power settings.
  • 0x01 (3f): Might be a status register indicating the current state or fault conditions.
  • 0x02 (20): Another configuration register, potentially for voltage control.

• 0x10 to 0x1F: Power management settings for different regulators.

  • 0x10 (08): Regulator voltage setting or enable/disable control.
  • 0x11 (06): Another voltage setting or related control register.

• 0x20 and beyond: Reserved or additional configuration registers.

  • Registers from 0x20 onwards are all 00, indicating they might not be used or are set to a default value.

For detailed interpretation, refer to the tps65217 datasheet.

7. Explore!

Get a dump from the other I2C devices on your BeagleBoard, you can use the i2cdump command similarly to how you did with the tps65217 device. Below are the steps for each device listed in your output:

14. Identifying Other I2C Devices

• From your previous output, you have several I2C devices on different buses. Here is a list of devices we can check:

  • Bus 0:

    • 0x4c - it66122 (HDMI CEC controller)
    • 0x50 - 24c256 (EEPROM)

  • Bus 2:

    • 0x54 to 0x57 - 24c256 (EEPROMs)

15. Remember the i2cdump command will only work if you unbind each driver.

16. Use the documentation for each chip to understand the output produced.

8. Summary