Unable to change I2C clock dtc

Question

Good afternoon dear friends,

The goal: -> Change i2c clock frequency to 400kHz

The motivation: -> Trying to use Adafruit BNO085 via i2c and there are known issues with rpi i2c clock stretching. (This is a known bug, has been going around since 2012. Yeah!)

What have I tried: I have spent a good two days reading into this topic and attempting multiple times to change the i2c clock frequency on my raspberry pi 4b running Ubuntu 22.04 Server (headless).

since I don't use rasbian I can NOT just edit a line in my boot-config file. But rather I have to disassemble, modify and recompile a device-tree file.

Followed this tutorial: Enable SPI and I2C on Ubuntu 20.04 Raspberry Pi

Applied to this file:

/boot/dtbs/5.15.0-1033-raspi/bcm2711-rpi-4-b.dtb

used this command to disassemble:

dtc -I dtb -O dts -o bcm2711-rpi-4-b.dts /boot/dtbs/5.15.0-1033-raspi/bcm2711-rpi-4-b.dtb

Then I modified these areas in that .dts (device-tree-source)

in the following two code chunks I replaced

clock-frequency = <0x186a0>; // 100000

with

clock-frequency = <0x61a80>; // 400000

Block 1

i2c@7e205000 {
compatible = "brcm,bcm2711-i2c\0brcm,bcm2835-i2c";
reg = <0x7e205000 0x200>;
interrupts = <0x00 0x75 0x04>;
clocks = <0x08 0x14>;
#address-cells = <0x01>;
#size-cells = <0x00>;
status = "disabled";
#clock-frequency = <0x186a0>; // 100000
clock-frequency = <0x61a80>; // 400000
phandle = <0x10>;
};

and also Block 2

i2c@7e804000 {
compatible = "brcm,bcm2711-i2c\0brcm,bcm2835-i2c";
reg = <0x7e804000 0x1000>;
interrupts = <0x00 0x75 0x04>;
clocks = <0x08 0x14>;
#address-cells = <0x01>;
#size-cells = <0x00>;
status = "disabled";
pinctrl-names = "default";
pinctrl-0 = <0x18>;
#clock-frequency = <0x186a0>; // 100000
clock-frequency = <0x61a80>; // 400000
phandle = <0x36>;
};

Further down I modified the following code Block:

#i2c1_baudrate = "\0\0\06clock-frequency:0"; // modified this
i2c1_baudrate = "\0\0\06clock-frequency:400000"; // modified this

Here the entire overrides Block

__overrides__ {
cam0-pwdn-ctrl;
cam0-pwdn;
cam0-led-ctrl;
cam0-led;
krnbt = "\0\0\00status";
krnbt_baudrate = "\0\0\00max-speed:0";
cache_line_size;
uart0 = "\0\0\01status";
uart1 = "\0\0\02status";
i2s = "\0\0\03status";
spi = "\0\0\04status";
i2c0 = [00 00 00 10 73 74 61 74 75 73 00 00 00 00 35 73 74 61 74 75 73 00];
i2c1 = "\0\0\06status";
i2c0_baudrate = [00 00 00 10 63 6c 6f 63 6b 2d 66 72 65 71 75 65 6e 63 79 3a 30 00];  // left this alone
#i2c1_baudrate = "\0\0\06clock-frequency:0"; // modified this
i2c1_baudrate = "\0\0\06clock-frequency:400000"; // modified this
audio = "\0\0\07status";
watchdog = "\0\0\08status";
random = "\0\0\09status";
sd_overclock = "\0\0\0:brcm,overclock-50:0";
sd_force_pio = "\0\0\0:brcm,force-pio?";
sd_pio_limit = "\0\0\0:brcm,pio-limit:0";
sd_debug = "\0\0\0:brcm,debug";
sdio_overclock = "\0\0\0;brcm,overclock-50:0\0\0\0\0<brcm,overclock-50:0";
axiperf = "\0\0\0=status";
arm_freq;
act_led_gpio = "\0\0\0>gpios:4";
act_led_activelow = "\0\0\0>gpios:8";
act_led_trigger = "\0\0\0>linux,default-trigger";
pwr_led_gpio = "\0\0\0?gpios:4";
pwr_led_activelow = "\0\0\0?gpios:8";
pwr_led_trigger = "\0\0\0?linux,default-trigger";
eth_led0 = "\0\0\0/led-modes:0";
eth_led1 = "\0\0\0/led-modes:4";
sd_poll_once = "\0\0\0@non-removable?";
spi_dma4 = <0x34 0x646d6173 0x3a303d00 0x41 0x34 0x646d6173 0x3a383d00 0x41>;
};

after that I re-compiled the .dts file back into .dtb using this command:

dtc -I dts -O dtb -o bcm2711-rpi-4-b.dtb bcm2711-rpi-4-b.dts

and then copied the file back into the directory where it was originally found and overwrote the existing file. Of course I have a backup.

sudo cp bcm2711-rpi-4-b.dtb /boot/dtbs/5.15.0-1033-raspi/bcm2711-rpi-4-b.dtb

But it still does not work. When executing the python test file from Adafruit I get the following error:

python3 imu_v2.py
    ********** Packet *************

DBG::        HEADER:
DBG::        Data Len: 17
DBG::        Channel: CONTROL (2)
DBG::           ** UNKNOWN Report Type **: 0x7c
DBG::        Sequence number: 19
DBG::        Data:
DBG::       [0x04] 0x7C 0x05 0x00 0x00 
DBG::       [0x08] 0x00 0x50 0xC3 0x00 
DBG::       [0x0C] 0x00 0x00 0x00 0x00 
DBG::       [0x10] 0x00 0x00 0x00 0x00 
DBG::       [0x14] 0x00 
        *******************************
Traceback (most recent call last):
  File "/home/administrator/Documents/raspberrypi_software/python/src/imu_v2.py", line 19, in <module>
    bno.enable_feature(BNO_REPORT_ROTATION_VECTOR)
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 999, in enable_feature
    self._process_available_packets(max_packets=10)
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 803, in _process_available_packets
    self._handle_packet(new_packet)
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 863, in _handle_packet
    raise error
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 858, in _handle_packet
    _separate_batch(packet, self._packet_slices)
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 373, in _separate_batch
    required_bytes = _report_length(report_id)
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 362, in _report_length
    return _AVAIL_SENSOR_REPORTS[report_id][2]
KeyError: 124

This is the program I'm trying to run, which according to adafruit documentation will require the i2c-clock-frequency to be at 400kHz.

import time
import board
import busio
from adafruit_bno08x import (
    BNO_REPORT_ACCELEROMETER,
    BNO_REPORT_GYROSCOPE,
    BNO_REPORT_MAGNETOMETER,
    BNO_REPORT_ROTATION_VECTOR,
)
from adafruit_bno08x.i2c import BNO08X_I2C
i2c = busio.I2C(board.SCL, board.SDA, frequency=400000)
#i2c = busio.I2C(board.SCL, board.SDA, frequency=100000)
bno = BNO08X_I2C(i2c)
bno.enable_feature(BNO_REPORT_ACCELEROMETER)
bno.enable_feature(BNO_REPORT_GYROSCOPE)
bno.enable_feature(BNO_REPORT_MAGNETOMETER)
bno.enable_feature(BNO_REPORT_ROTATION_VECTOR)
while True:
    time.sleep(0.5)
imu_data = {}

accel_x, accel_y, accel_z = bno.acceleration  # pylint:disable=no-member
imu_data["linear_acceleration"] = {"x": accel_x, "y": accel_y, "z": accel_z}

gyro_x, gyro_y, gyro_z = bno.gyro  # pylint:disable=no-member
imu_data["angular_velocity"] = {"x": gyro_x, "y": gyro_y, "z": gyro_z}

mag_x, mag_y, mag_z = bno.magnetic  # pylint:disable=no-member
imu_data["magnetic_field"] = {"x": mag_x, "y": mag_y, "z": mag_z}

quat_i, quat_j, quat_k, quat_real = bno.quaternion  # pylint:disable=no-member
imu_data["orientation"] = {"x": quat_i, "y": quat_j, "z": quat_k, "w": quat_real}

# Populate the 3x3 covariance matrices with zeros (assuming no covariance)
imu_data["orientation_covariance"] = [0.0] * 9
imu_data["angular_velocity_covariance"] = [0.0] * 9
imu_data["linear_acceleration_covariance"] = [0.0] * 9

print(imu_data)
print("")

And yes, I tried with both 100000 and 400000 as you can see in the script.

And here the output it produces, before it crashes and produces an error-trace, which can be found further down. Please note the output is heavily redacted due to repetitive information. Usually runs for about 10-15s before crashing. Could be some buffer filling up?

administrator@hostname:~/Documents/raspberrypi_software/python/src$ python3 imu_v2.py 
{'linear_acceleration': {'x': 0.3046875, 'y': -0.11328125, 'z': 9.578125}, 'angular_velocity': {'x': 0.001953125, 'y': 0.0, 'z': 0.0}, 'magnetic_field': {'x': -4.0, 'y': -9.5625, 'z': 54.4375}, 'orientation': {'x': -0.005615234375, 'y': -0.01409912109375, 'z': 0.0001220703125, 'w': 0.9998779296875}, 'orientation_covariance': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0], 'angular_velocity_covariance': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0], 'linear_acceleration_covariance': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]}
{'linear_acceleration': {'x': 0.26953125, 'y': -0.11328125, 'z': 9.58203125}, 'angular_velocity': {'x': 0.0, 'y': 0.0, 'z': 0.0}, 'magnetic_field': {'x': -4.75, 'y': -11.375, 'z': 49.75}, 'orientation': {'x': -0.00567626953125, 'y': -0.01416015625, 'z': 6.103515625e-05, 'w': 0.9998779296875}, 'orientation_covariance': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0], 'angular_velocity_covariance': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0], 'linear_acceleration_covariance': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]}
<data ommited>
    Large chunk of data ommited due to character limit
</data ommited>
{'linear_acceleration': {'x': 0.3046875, 'y': -0.15234375, 'z': 9.578125}, 'angular_velocity': {'x': 0.0, 'y': 0.0, 'z': 0.0}, 'magnetic_field': {'x': -4.0, 'y': -9.9375, 'z': 54.1875}, 'orientation': {'x': -0.0064697265625, 'y': -0.015380859375, 'z': -6.103515625e-05, 'w': 0.9998779296875}, 'orientation_covariance': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0], 'angular_velocity_covariance': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0], 'linear_acceleration_covariance': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]}

And finally the error trace that appears after 10-15s of above output:

        ********** Packet *************
DBG::        HEADER:
DBG::        Data Len: 191
DBG::        Channel: INPUT_SENSOR_REPORTS (3)
DBG::           Report Type: BASE_TIMESTAMP (0xfb)
DBG::           Sensor Report Type: ACCELEROMETER(0x1)
DBG::        Sequence number: 87
DBG::        Data:
DBG::       [0x04] 0xFB 0xFB 0x12 0x00 
DBG::       [0x08] 0x00 0x01 0xE1 0x02 
DBG::       [0x0C] 0x00 0x45 0x00 0xE3 
DBG::       [0x10] 0xFF 0x95 0x09 0x03 
DBG::       [0x14] 0xD1 0x00 0x16 0xB4 
DBG::       [0x18] 0xFF 0x56 0xFF 0x44 
DBG::       [0x1C] 0x03 0x05 0xD0 0x00 
DBG::       [0x20] 0x7A 0x99 0xFF 0x00 
DBG::       [0x24] 0xFF 0x00 0x00 0x7E 
DBG::       [0x28] 0xBF 0x44 0x32 0x01 
DBG::       [0x2C] 0xE2 0x06 0x3D 0x4E 
DBG::       [0x30] 0x00 0xE3 0xFF 0x94 
DBG::       [0x34] 0x09 0x02 0xD2 0x04 
DBG::       [0x38] 0x3F 0x00 0x00 0x00 
DBG::       [0x3C] 0x00 0x00 0x00 0x03 
DBG::       [0x40] 0xD2 0x08 0x0B 0xBA 
DBG::       [0x44] 0xFF 0x56 0xFF 0x2B 
DBG::       [0x48] 0x03 0x05 0xD1 0x08 
DBG::       [0x4C] 0x6F 0x98 0xFF 0x00 
DBG::       [0x50] 0xFF 0x00 0x00 0xFE 
DBG::       [0x54] 0x3F 0x44 0x32 0x01 
DBG::       [0x58] 0xE3 0x0A 0x78 0x4E 
DBG::       [0x5C] 0x00 0xD9 0xFF 0x94 
DBG::       [0x60] 0x09 0x02 0xD3 0x0C 
DBG::       [0x64] 0x37 0x00 0x00 0x00 
DBG::       [0x68] 0x00 0x00 0x00 0x01 
DBG::       [0x6C] 0xE4 0x0E 0xB6 0x45 
DBG::       [0x70] 0x00 0xE3 0xFF 0x95 
DBG::       [0x74] 0x09 0x03 0xD3 0x10 
DBG::       [0x78] 0x00 0xBA 0xFF 0x5B 
DBG::       [0x7C] 0xFF 0x38 0x03 0x05 
DBG::       [0x80] 0xD2 0x10 0x63 0x98 
DBG::       [0x84] 0xFF 0x00 0xFF 0x00 
DBG::       [0x88] 0x00 0xFE 0x3F 0x44 
DBG::       [0x8C] 0x32 0x01 0xE5 0x12 
DBG::       [0x90] 0xF7 0x4E 0x00 0xE3 
DBG::       [0x94] 0xFF 0x8A 0x09 0x02 
DBG::       [0x98] 0xD4 0x14 0x2C 0x00 
DBG::       [0x9C] 0x00 0x00 0x00 0x00 
DBG::       [0xA0] 0x00 0x03 0xD4 0x14 
DBG::       [0xA4] 0xF4 0xB4 0xFF 0x5B 
DBG::       [0xA8] 0xFF 0xB1 0x03 0x01 
DBG::       [0xAC] 0xE6 0x1A 0x36 0x4E 
DBG::       [0xB0] 0x00 0xE3 0xFF 0x94 
DBG::       [0xB4] 0x04 0xFF 0xFF 0xFF 
DBG::       [0xB8] 0xFF 0xFF 0xFF 0xFF 
DBG::       [0xBC] 0xFF 0xFF 0xFF 0xFF 
DBG::       [0xC0] 0xFF 0xFF 0xFF 
        *******************************
Traceback (most recent call last):
  File "/home/administrator/Documents/raspberrypi_software/python/src/imu_v2.py", line 26, in <module>
    accel_x, accel_y, accel_z = bno.acceleration  # pylint:disable=no-member
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 598, in acceleration
    self._process_available_packets()
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 803, in _process_available_packets
    self._handle_packet(new_packet)
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 863, in _handle_packet
    raise error
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 858, in _handle_packet
    _separate_batch(packet, self._packet_slices)
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 373, in _separate_batch
    required_bytes = _report_length(report_id)
  File "/home/administrator/.local/lib/python3.10/site-packages/adafruit_bno08x/init.py", line 364, in _report_length
    return _REPORT_LENGTHS[report_id]
KeyError: 255

Not sure what I'm missing. At this point I'm still not sure if my bus has actually changed clock-frequency. Does anyone know:

1. how to check the clock-frequency of i2c on rpi 4b running Ubuntu 22.04 (NOT raspbian)
2. what I am missing, what's wrong here?

Answer 1

I was able to solve this problem and wanted to post the solution, for anyone else who:

1. has a raspberry pi running Ubuntu
2. needs to change the i2c clock speed (from 100000 to 400000)

After this excursion into dts and dtb it was decided to simply use dt-overlays.

First I created a new file "i2c1-frequency-overlay.dts"

// i2c1-frequency-overlay.dts
/dts-v1/;
/plugin/;
/ {
    compatible = "brcm,bcm2711";
    fragment@0 {
        target = <&i2c1>;
        __overlay__ {
            clock-frequency = <400000>; // Set your desired frequency here (e.g., 400 kHz)
        };
    };
};

Second I compiled this file using:

dtc -I dts -O dtb -o i2c1-frequency-overlay.dtbo i2c1-frequency-overlay.dts

This created the dtb file

i2c1-frequency-overlay.dtbo

which then was copied to /boot/firmware/overlays/

sudo cp i2c1-frequency-overlay.dtbo /boot/firmware/overlays/

Next I modified /boot/firmware/config.txt

sudo nano /boot/firmware/config.txt

and appended the following:

# Added below to change i2c frequency from 100kHz [default] to 400kHz [fast mode]
dtparam=i2c_arm_baudrate=400000
dtoverlay=i2c1-frequency-overlay

Last step reboot

sudo reboot

Just to verify the i2c clock frequency updated:

// this did not work:
cat /sys/class/i2c-adapter/i2c-1/of_node/clock-frequency

did some more research and found the following

// but this worked
echo 0x$(xxd /sys/class/i2c-adapter/i2c-1/of_node/clock-frequency | cut -f 2,3 -d ' ' --output-delimiter='') | xargs printf "%d\n"
-bash: warning: command substitution: ignored null byte in input
400000

-> this confirms the bus is at 400kHz :-)