The debug path to EFM32 is blocked when:

• I disabled the debug pin
• I stopped the HF oscillator that supplies the clock to the core
• migrated to EM4

Of course, resetting restores the debug path once, but if the above processing was executed in the beginning of the user code, the user code would cut off the debug path again immediately after the reset was released, causing the debugger to It will remain inaccessible. (Example: User code that suddenly shifts to EM4 immediately after reset)
I will show you how to recover in this case.

1. If the recovery target is the user board, switch the debug target. Select Out in the Debug Mode selection menu of Kit Manager.
2. Click Flash Programmer.

3. Click Unlock Debug Access. The flash memory contents are erased and the debug path is restored.

Please refer to the Silicon Labs community site for the mechanism.