9.4.10.4 Enabling IRT

By default (erased UCB area), IRT is disabled. When IRT is disabled, IRT regions (if any) are not protected, and access to the region from firmware outside the IRT regions is only dependent on the region’s Flash protection configuration bits, if configured.

IRT is enabled by the IRT (FIRT[0]) configuration bit in the UCB area. When IRT is enabled, a permanent immutable protection region with IRT firmware must be configured at the beginning of the user program Flash. This region functions as the boot ROM for the device. This region may be an OTP region or an IRT region with write permission disabled (via Flash protection configuration bits). OTP region firmware can be shared between the IRT and other firmware components. IRT regions are only truly permanent once either the UCB erase-protect and/or UCB write-protect words are programmed. During development, the UCB erase and write-protect words may be left unprogrammed.