Register Initialization Parameters — 0x0A0 to 0x89C - Register Initialization Parameters — 0x0A0 to 0x89C - 1.15 English - UG585

This region contains 256 pairs of address and data words that can be used to initialize PS registers for the MIO multiplexer, boot device clocks, and other functions before the FSBL/User code is accessed from the boot device; either to copy the image to the OCM or to execute-in-place. The register writes are commonly used to optimize the boot device interface and set its clock frequency to maximize performance.

A register initialization pair appears as two 32-bit words, first a register address, then a register write value. Register initializations can be in any order, and the same register can be initialized with different values as many times as desired. The register initialization is performed prior to copying the FSBL/User code so the user can modify the default reset register values to reduce the time to access the code and process it.

The BootROM stops processing the Register Initialization list when either the address register = 0xFFFF_FFFF or the end of the list (256 address/write data pairs).

Usage of the register initialization parameters are explained in the “Register Initialization to Optimize Boot Times” section of BootROM Performance.

Restricted Addresses

The register address space for the Register Initialization address-data writes is restricted. Register addresses outside of the allowed address range cause the BootROM to lockdown the system and generate error code 0x2111. The allowed register accesses depend on the boot mode and are listed in the following table.

These restrictions are enforced by the BootROM. They do not apply when the FSBL/User code begins to execute. The BootROM screens the register initialization writes and disallows certain addresses from being accessed.