Hello - SBL has enabled a new feature - source level debugging over serial port with Intel UDK debugger. This feature will allow users to debug each SBL stages in source level and supports Apollolake and QEMU targets currently. By default, this feature is disabled for boot performance consideration. To enable this feature, please refer to Source Level Debugging(https://slimbootloader.github.io/developer-guides/debugging-with-udk.html) user guide. Best Regards, Aiden