SDAA136 December   2025 AM62L , AM62P

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2HS Device Flashing With Boot Mode Switch
  6. 3HS Device Flashing Without Boot Mode Switch
    1. 3.1 Design 1: Booting from Backup Boot Media
    2. 3.2 Design 2: Booting from Primary Boot Media
  7. 4 Summary

2 HS Device Flashing With Boot Mode Switch

The typical boot flow of using Keywriter for mass production is Memory A boot mode and Memory B boot mode.

Here is an example:

  1. Use an SD card as the boot medium (1) and store the keywriter boot image on the SD card. Use Norflash as the boot medium (2) and burn the service boot image and application offline at the factory.
  2. Set the boot mode to SD card for the first power-up. Based on the boot mode setting, the Boot ROM reads the keywriter from the SD card, burns the customer key into the OTP area of the chip, and converts the chip from HS-FS to HS-SE.
  3. Power off and switch the boot mode to OSPI boot mode.
  4. Power on again, the Boot ROM reads the service boot image from the OSPI Norflash. Since the boot image is signed and encrypted, the Boot ROM verifies and decrypts the signature using the Boot ROM's X509 header, and then boots the cores normally.
Typical Boot Flow with Boot Mode Switch Figure 2-1 Typical Boot Flow with Boot Mode Switch
SD Card as First Boot, OSPI Boot as Second Boot Figure 2-2 SD Card as First Boot, OSPI Boot as Second Boot

This design is relatively mature, avoiding many reliability and field operation issues by switching the boot mode in a single operation.

However, compatibility with both memory boot modes increases BOM costs and design complexity. A second issue is that switching the boot mode requires additional jigs, which complicates the production line. Furthermore, this boot mode switching often requires manual intervention, further reducing production line efficiency and increasing the rate of issues.