19.1.4.2 Boot Configuration Packet

The boot configuration data are stored in the Boot Configuration Packet in the OTP User area. These data can be used for various boot sequence customizations:
  • Enable and configure the boot from selected memories
  • Configure the UART port used as a console
  • Disable monitor

See Boot Configuration User Interface for a detailed description of all the fields in these data.

Out of factory, the OTP memory is empty. No Boot Configuration Packet is written. During the prototyping phase, the Boot Configuration Packet can be created and stored in a backed up OTP emulation SRAM to avoid an OTP permanent write. To enable this feature, the bit BSC_CR.EMUL_EN must be set. Note that once a real packet has been written in OTP User Area, the Emulation mode cannot be used anymore.

The current running mode of the OTP can be observed by reading BSC_CR.EMUL_EN. If this bit is set, the OTP Emulation mode is enabled, otherwise it is disabled.

After a reset, the ROM code reads the Boot Configuration Packet from the OTP emulation SRAM if the bit BSC_CR.EMUL_EN is set to 1. Otherwise, the packet is read from the OTP matrix.

The OTP Emulation mode enables the user to test several boot configuration options, including Secure Boot Mode (see Secure Boot Strategy), without programming permanently the OTP.

Note: The OTP emulation SRAM is backed up. So, if the VDDBU power is supplied, the boot configuration is kept when the chip in not powered on.
Warning: The Boot Configuration Packet must be the very first packet to be written in OTP (not in Emulation mode).
Figure 19-2. Boot Configuration Loading