The Kinetis family and i.MX RT series of MCUs are pre-manufactured with the MCU bootloader in either the ROM or flash memory of the device, and can boot into the MCU bootloader application.
MCU Bootloader Manufacturing Tool User's Guide
The Kinetis family and i.MX RT series of MCUs are pre-manufactured with the MCU bootloader in either the ROM or flash memory of the device, and can boot into the MCU bootloader application.