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Use on Radxa Cubie A7Z

The default I2C frequency for i2c-7 on the Radxa Cubie A7Z is set to 400kHz. However, in some cases, this may lead to instability in detecting the PiSugar3 battery device. This document provides a step-by-step guide to downclock i2c-7 to 100kHz, which can improve the detection success rate of the battery device.

Applicable Scenarios​

  • PiSugar3 power supply and physical wiring have been confirmed to be normal.
  • The initial scan of i2c-7 does not show the battery device address (or only shows other devices).

Environment Information (Tested in This Case)​

  • Board: Radxa Cubie A7Z
  • System Kernel: 5.15.147-14-a733
  • I2C Controller: /sys/firmware/devicetree/base/soc@3000000/twi@2517000
  • I2C Device Node: /dev/i2c-7
  • TWI7 overlay: /boot/dtbo/sun60iw2p1-twi7.dtbo

1 Baseline Check (Before Downclocking)​

ssh radxa@<radxa-ip>
printf 'radxa\n' | sudo -S /usr/sbin/i2cdetect -y 7

Observed phenomenon (before downclocking):

  • No device detected, the battery device address does not appear.

2 Confirm Current Frequency​

printf 'radxa\n' | sudo -S xxd -g 1 /sys/firmware/devicetree/base/soc@3000000/twi@2517000/clock-frequency

Output 00 06 1a 80, i.e. 0x00061A80 = 400000 (400kHz).

3 Modify TWI7 Overlay Frequency to 100kHz​

Core idea: Decompile dtbo -> modify clock-frequency -> recompile and overwrite -> reboot.

printf 'radxa\n' | sudo -S sh -c '
cp -a /boot/dtbo/sun60iw2p1-twi7.dtbo /boot/dtbo/sun60iw2p1-twi7.dtbo.bak-400k
dtc -I dtb -O dts -o /tmp/sun60iw2p1-twi7.dts /boot/dtbo/sun60iw2p1-twi7.dtbo
sed -i "s/clock-frequency = <0x61a80>/clock-frequency = <0x186a0>/" /tmp/sun60iw2p1-twi7.dts
dtc -@ -I dts -O dtb -o /boot/dtbo/sun60iw2p1-twi7.dtbo /tmp/sun60iw2p1-twi7.dts
reboot
'

Notes:

  • 0x61a80 = 400000 (400kHz)
  • 0x186a0 = 100000 (100kHz)

4 Verification After Reboot​

4.1 Frequency Confirmation​

printf 'radxa\n' | sudo -S xxd -g 1 /sys/firmware/devicetree/base/soc@3000000/twi@2517000/clock-frequency

You should see 00 01 86 a0 (100kHz).

4.2 Bus Scan​

printf 'radxa\n' | sudo -S /usr/sbin/i2cdetect -y 7
printf 'radxa\n' | sudo -S /usr/sbin/i2cdetect -r -y 7

Observed phenomenon (after downclocking):

  • 0x57 newly appears (not present before downclocking).
  • In -r mode, 0x57 is visible (and 0x68 can be observed).

4.3 Register Read Connectivity Test​

printf 'radxa\n' | sudo -S sh -c '
/usr/sbin/i2cget -y 7 0x57 0x00
/usr/sbin/i2cget -y 7 0x57 0x01
/usr/sbin/i2cget -y 7 0x57 0x02
'

Returned values in this test:

  • 0x03
  • 0x0f
  • 0xec

Indicates that the 0x57 device is communicable.

5 Rollback to 400kHz​

If you want to restore the original frequency, simply restore the backup file and reboot:

printf 'radxa\n' | sudo -S sh -c '
cp -a /boot/dtbo/sun60iw2p1-twi7.dtbo.bak-400k /boot/dtbo/sun60iw2p1-twi7.dtbo
reboot
'

6 Common Issues​

  • i2cdetect: command not found
    • Use the absolute path: /usr/sbin/i2cdetect
  • sudo cannot be executed non-interactively
    • Use printf 'password\n' | sudo -S ..., or log in first and enter manually.
  • Still unstable
    • You can try 50kHz (0x0000c350) for further comparison.

Configuration for pisugar-server​

After successfully detecting the battery device, you can proceed to configure the pisugar-server to read battery information. Edit the configuration file /etc/pisugar-server/config.json to specify the I2C bus:

{
  "i2c_bus": 7,
}

Then restart the pisugar-server service:

sudo systemctl restart pisugar-server

All set! You should now be able to read battery information through the pisugar-server webUI.