The basic idea of ​​this design is to offline burn the required files to the Nor flash at specified offsets. These files include three bootloaders.

• The first bootloader is a Keywriter located at address 0x0, which is used to burn the key.
• The second bootloader is a Flash Writer located at address 0x400000. This flash writer is single stage SBL/SPL based with the only job of moving the SBL from known location X to primary offset 0x0 and optionally redundant offset 0x400000.
• The third bootloader contains the boot loader from the customer and application (pre-signed and encrypted with the key from the customer). The address can be flexibly configured based on the selected Nor flash capacity, and the requirement is that the addresses do not overlap with the first two bootloaders.

During the first power-up, the program executes from the keywriter at address 0x0, converting the chip from HS-FS to HS-SE. During the second power-up, the BootROM fails to verify the keywriter at address 0x0 and jumps to address 0x400000 to execute the flash writer. This program burns the service startup program of the customer and application (pre-signed and encrypted with the key from the customer) to address 0x0 in the flash memory, overwriting the previous keywriter file. At this time, after powering on again, the Boot ROM normally reads the business startup program and application from address 0x0, completes the key signature verification and decryption, and then completes the boot and starts the SOC.

Requirements

Boot mode => Primary: OSPI, Backup: (Don't care)

Flash is offline flashed with three parts of files on related offset.

Procedure

1. On First POR: Device state: HS-FS. ROM boots OTP Keywriter from the 0x0 Nor flash offset. Program the keys according to the Keywriter guide. Convert HS-FS to HS-SE.
2. On Second POR: Device state: HS-SE. ROM boots Flash Writer from the 0x400000 Nor flash offset. Flash the SDK images (SBL/Applications) into 0x0, 0x8000.
3. On Third POR: Device state: HS-SE. ROM boot customer bootloader and application from 0x0 offset and bring up board.