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I have a Raspberry Pi 4 model B, fresh installation of Raspberry Pi OS. I am trying to use software i2c to get around the clock stretch bug in the broadcom 2835 chip.

I edit /boot/config.txt to contain the following line

dtoverlay=i2c-gpio,i2c_gpio_sda=4,i2c_gpio_scl=5

I save it and reboot but then the Pi hangs after the first multicolor splash screen on boot. Editing this file again and commenting this line out allows the pi to boot as expected.

I've also tried just a simple line

dtoverlay=i2c-gpio

Which should have automatically used bus 3, and gpio pins 23 and 24. Still same boot hang. I've gone through a number of combinations of explicit bus and pin setting with no dice.

Anyone have any thoughts?

EDIT: Full config.txt

# For more options and information see
# http://rpf.io/configtxt
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable infrared communication.
#dtoverlay=gpio-ir,gpio_pin=17
#dtoverlay=gpio-ir-tx,gpio_pin=18

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on

[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
dtoverlay=vc4-fkms-v3d
max_framebuffers=2

[all]
#dtoverlay=vc4-fkms-v3d
dtoverlay=i2c-gpio,bus=3,i2c_gpio_sda=2,i2c_gpio_scl=3
  • Full contents of config.txt. Photo of connections to Pi during boot. – joan Jun 2 at 7:26
  • I've added config.txt to the main question. I don't have anything connected to the i2c bus or any pins during debug. – user2434545 Jun 2 at 14:44

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