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Sergey Korol avatar Ubuntu

Additional i2c_gpio is not detected on Ubuntu Server 20.04 / RPi Zero 2 W / A+

pg flag
Sergey Korol

I'm trying to enable the second (GPIO-based i2c) on RPi Zero 2 W, Ubuntu server 20.04 to connect the following sensor. Note that the primary i2c pins are physically occupied as RPi is used as a hat for another board. I've read tons of articles / similar questions, but have no luck detecting the sensor.

Here's my /boot/config.txt:

start_x=1
enable_uart=1
dtparam=i2c_arm=on 
dtoverlay=i2c-gpio,bus4,i2c_gpio_delay_us=8,i2c_gpio_sda=23,i2c_gpio_scl=24

Here's the actual wiring: wiring

I've also added 2x4.7 resistors for SDA and SCL according to recommendations. Well, I tried w/o resistors as well.

When I run i2cdetect -l, I see only a default bus:

ubuntu@rpi:~$ i2cdetect -l
i2c-1   i2c         bcm2835 (i2c@7e804000)              I2C adapter

Which obviously gives nothing for i2cdetect -y 1:

ubuntu@rpi:~$ i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --

I see a sensor only if I connect it to the primary i2c port:

ubuntu@rpi:~$ i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- 77

Here's additional system info:

ubuntu@rpi:~$ uname -a
Linux rpi 5.4.0-1050-raspi #56-Ubuntu SMP PREEMPT Thu Jan 13 13:09:35 UTC 2022 aarch64 aarch64 aarch64 GNU/Linux

Note that I've already tried to upgrade the kernel, but it seems like Ubuntu 20.04 has stuck on the 5.4 version.

Any thoughts would be greatly appreciated.

UPDATES

  • 2022/01/31: added dmesg logs.
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ch flag
Serg
Do you see something interesting regarding your interface in `dmesg` output?
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Sergey Korol avatar
pg flag
Sergey Korol
@Serg I updated the post with a link to dmesg log. I see some issues with spi and encodings. But I'm not sure if it has a direct relationship with the original problem. Maybe you can find something interesting there.
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ch flag
Serg
It's hard to say definitely in your case as you tried many things. First, maybe omit bus definition, i.e. remove `bus4` from `dtoverlay` - let it be provided by system. And also maybe try to explicitly enable support of appropriate `i2c-rtc` device.
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Sergey Korol avatar
pg flag
Sergey Korol
@Serg tried to remove the bus, but it didn't help. Not sure regarding an explicit `i2c-rtc` device support though. Did you mean smth like this: https://gist.github.com/Lahorde/2bc5e4a3b69fc6ca5797?
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ch flag
Serg
Yes, something of that kind as you provided in GitHub link.
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Sergey Korol avatar Ubuntu
pg flag
Sergey Korol

Ok, after a number of experiments I came up with the fact that Ubuntu on RPi ignores /boot/config.txt settings for some reason (or just overwrites them) in favor of /boot/firmware location. I examined /boot/firmware/syscfg.txt and found the same settings there. So then I've just blindly added dtoverlay=i2c-gpio,... to syscfg and after reboot, my i2c sensor magically appeared in the list. That's weird and disappointing as all the guides mention /boot/config.txt as a single point of truth. I wasted so many hours on that.

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