Some configuration information such as clock trim values stored in factory programmedflash locations is autoloaded.6.3.1 Boot sourcesThe CM0+ core adds support for a programmable Vector Table Offset Register (VTOR)to relocate the exception vector table. This device supports booting from:• internal flash• ROMThis device supports booting from internal flash with the reset vectors located ataddresses 0x0 (initial SP_main), 0x4 (initial PC).The device is also able to boot from ROM. The ROM start address is from 0x1C00_0000.When boot from ROM, it remaps all vector fetch to ROM base address. ROM code startpointer locates in ROM vector table which address is 0x1C00_0000 where stack pointeris offset 0x0 and reset vector is offset 0x4. Vector table and stack pointer are valid out ofreset. RCM mode register is cleared by software when Boot ROM completes, thisdisables remapping of vector fetches. Boot source can change between reset, but isalways known before core reset negation. NMI input is disabled to platform whenbooting from ROM. See FOPT section and Reset Control Module for more detail options.The boot options can be overridden by using RCM_FM[2:1] and RCM_MR[2:1] whichcan be written by software. The boot source remains set until the next System Reset orsoftware can write logic one to clear one or both of the mode bits.6.3.2 FOPT boot optionsThe Flash Option (FOPT) register in the Flash Memory module (FTFA_FOPT) allowsthe user to customize the operation of the MCU at boot time. The register contains read-only bits that are loaded from the NVM's option byte in the flash configuration field. Thedefault setting for all values in the FTFA_FOPT register is logic 1 since it is copied fromthe option byte residing in flash, which has all bits as logic 1 in the flash erased state. Toconfigure for alternate settings, program the appropriate bits in the NVM option byte.The new settings will take effect on subsequent POR, VLLSx recoveries, and any systemreset. For more details on programming the option byte, see the flash memory chapter.Chapter 6 Reset and BootKL27 Sub-Family Reference Manual , Rev. 5, 01/2016Freescale Semiconductor, Inc. 85
