9.3.1 CRC Scan of Boot ROM

The Boot ROM performs a CRC scan of the Boot ROM as part of the boot process. Any fault detected in the Boot ROM will lead to:

• The Machine Check Reset Flag (MCRF) bit in the Reset Flag (RSTCTRL.RSTFR) register, and the Error Detected During System Start-up (BOOT) bit in the Machine Flags A (RSTCTRL.MCFLAGSA) register are set
• The device is reset

In the case of a random or transient failure in the Boot ROM - The user can observe the nature of such a failure by reading RSTCTRL flag registers through the UPDI interface after the next (successful) boot process.

In the case of a permanent failure in the Boot ROM - The device will be stuck in an endless reset loop, never exiting the boot process. The UPDI is not allowed to read RSTCTRL while in the boot process, so to diagnose this problem, the user will have to poll the BOOTDONE bit in the ASI System Status (UPDI.ASI_SYS_STATUS) register and verify that it never gets set.

In a locked device, the UPDI does not have access to the RSTCTRL flag registers.