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Some configuration information such as clock trim values stored in factory programmed
flash locations is autoloaded.
6.3.1 Boot sources
The 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
• ROM
This device supports booting from internal flash with the reset vectors located at
addresses 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 start
pointer locates in ROM vector table which address is 0x1C00_0000 where stack pointer
is offset 0x0 and reset vector is offset 0x4. Vector table and stack pointer are valid out of
reset. RCM mode register is cleared by software when Boot ROM completes, this
disables remapping of vector fetches. Boot source can change between reset, but is
always known before core reset negation. NMI input is disabled to platform when
booting from ROM. See FOPT section and
The boot options can be overridden by using RCM_FM[2:1] and RCM_MR[2:1] which
can be written by software. The boot source remains set until the next System Reset or
software can write logic one to clear one or both of the mode bits.
6.3.2 FOPT boot options
The Flash Option (FOPT) register in the Flash Memory module (FTFA_FOPT) allows
the 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. The
default setting for all values in the FTFA_FOPT register is logic 1 since it is copied from
the option byte residing in flash, which has all bits as logic 1 in the flash erased state. To
configure 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 system
reset. For more details on programming the option byte, see the flash memory chapter.
Freescale Semiconductor, Inc.
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
Reset Control Module
Chapter 6 Reset and Boot
for more detail options.
85
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