Linux - Raspberry Pi 5 does multiple I2C buses like a champ

 This was killing me.  The rp5 is such a magnificent machine for python development.  I use the AI Qwen to write the python programs.  For some reason, Google Gemini sucks at it, even 2.5.  can't wait to see how I can do the Adxl355.  There seems to be a universal timing problem there.

A few minutes of tinkering time.
Bought https://www.ebay.co.uk/itm/167295678646 modules. Soldered the header on, and bridged CS to VCC to select I2C mode.
Pi wiring:
VCC to Pi pin 1 (3V3)
SDA to Pi pin 3 (GPIO2 / SDA)
SCL to Pi pin 5 (GPIO3 / SCL)
INT1 to Pi pin 7 (GPIO 4)
GND to Pi pin 9 (GND)

ADXL345 is supported by the adxl34x driver at https://github.com/torvalds/linux/blob/ ... l34x-i2c.c
Add the relevant config to the i2c-sensor overlay - now a pull request at https://github.com/raspberrypi/linux/pull/6712

Add "dtoverlay=i2c-sensor,adxl345" to /boot/firmware/config.txt, and I have an extra input device that gives me positional readouts.

Change config to "dtoverlay=i2c-sensor,adxl345,i2c0". Power down. Rewired SDA and SCL to pins 27 & 28 respectively (GPIOs 0&1). Power up. I have the same input device present and giving me positional readout.
The overlay has all the hardware I2C buses available as overrides, as documented by "dtoverlay -h i2c-bus".

If you wish to use a bitbashed I2C bus, then use "dtoverlay=i2c-gpio,i2c_gpio_sda=0,i2c_gpio_scl=1,bus=8", and "dtoverlay=i2c-sensor,adxl345,i2c-path=i2c@8" (substitute the 8 with the bus number of your choice that isn't already taken, and 0 & 1 with the GPIOs of your choice).

I just did the bus 0 on pins 27&28 and it worked perfectly.  I think the i2c device thing is critical.  The '355' may need a new device, or this one works.  A device file only has a few extra droverlay commands.

All the rp's are quite fussy about putting things in config.txt and rebooting.  I powered off for extra oomph.  My main goal is to put a lot of '345's on a base and running an array.  This can do rotation and tilt and can reduce internal noise.  However, on adxl355 can do for many 345's and I have dreams.  However, the adxl355 has never been shown to work on i2c, and rp5.

This solution was on the rp forums.

ps.  the main problem was that there are a number of pi models, and although you specify rp5, the search engines don't do that.  As well, the rp5 has a completely different gpio chip, and runs Debian bookworm.  They have made great progress to unify everything.