• I2C
  • Beginner
  • 5 min
  • Serial CLI

Recipe · Beginner · I2C

How to recover a stuck I2C bus

An I2C board scanned once, then disappeared. SDA looked stuck low after a failed transaction. This recipe uses the firmware recovery command before touching the soldering iron.

I2C bus recovery signal.
Before rewiring everything, clock the bus and send a stop condition to release a stuck target.

Wiring View

I2C board BP SDAI2C SDA GPIOSCLI2C SCL GPIOGNDBP GNDVCCcorrect supply
Generated from the wiring summary: I2C board to BP.
Step 1

Commands

Run the typed commands first. If the command opens an interactive shell, select the named action from the shell menu instead of treating it as another CLI command.

Result

What success looks like

If the next scan finds the target again, the issue was likely a stuck transaction. If not, inspect voltage, pull-ups and wiring.

Troubleshooting

  • Running recovery while another master is actively driving the bus.
  • Assuming recovery fixes missing pull-ups or wrong voltage.
  • Keeping a target powered from a different ground reference.

Next steps

  • Run scan again after recovery.
  • Use ping <addr> if you know the address.
  • Use trace or monitor only after the bus is stable.

I2C bus recovery FAQ

What does I2C bus recovery actually do?

Recovery toggles SCL and sends a stop condition so a target that is stuck mid-transaction can release SDA. It is a bus-state reset, not a fix for wrong wiring, missing pullups or bad voltage.

When should I avoid running I2C recover?

Avoid it while another master is actively controlling the bus or when the target is in the middle of a critical operation. On a shared system, isolate the bench setup before forcing clocks.

What does I2C recovery actually try to do?

Recovery attempts to clock the bus so a target that is holding SDA can release the line. It is a bus-state recovery helper, not a substitute for correct wiring or target power.

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