Silicon Labs EFx32 Series 2

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This article covers device specific details shared by all EFM32/EFR32 Series 2 devices (following called "EFx32"). The Silicon Labs EFx32 devices are Cortex-M33 MCUs.

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Secure boot specific

All EFx32 devices support a secure boot mode. Once enabled, this state is permanent and cannot be reverted. In this mode, the bootloader will check the flashed application for validity and prevent it from booting if it is invalid. If an invalid application is found by the bootloader after reset, it will lock debug functionality of the device.

Debugging with invalid application

To allow debugging in case the device is in secure boot state and the application is invalid (e.g. erased state, unsigned application, ...), the J-Link will ask the user for permission to mass erase the device.


The following things have to be considered in this state:

  • If mass erase is disabled, gaining debugging access is impossible.
  • Resetting the device will lock debug access again until the next mass erase
  • The Debug Challenge Interface (DCI) will be disabled after debug access was granted.

This is especially important for the following scenarios:

  • Debugging an invalid application on the device: Mass erase & programming is required after each reset.
  • When flashing/erasing the device: Device must not be reset beforehand. Otherwise debug connection is lost and the attempt fails.
  • User Datat Page programming on EFx32G21: UDP can only be programmed via DCI. As DCI is disabled in this state while debug access is granted, programming will not be possible. A valid application has to be programmed first.

Debug lock

J-Link supports native debug unlock via mass erase during connect. In case a locked device is detected the user will be asked for permission before the device is mass erased.

Debug unlock is only possible while mass erase is enabled.