33.2.8.1 CFG Read Protect (CRP)
CRP *RP bits provide read protection for CFM pages. Some CFM pages may contain secret information accessible only to the Boot ROM code. The Boot ROM can protect and lock these page before it exits. The BootCfg page contains values to be used by the Boot ROM to program the CRP register before allowing boot flash to execute. See the device spec for this location do so. When read protected, read of this page cause a bus error.
If TrustZone is enabled on the device, then pages not used by the Boot ROM could be left unlocked such that trusted code has the option to select the page settings. However, if the device is not a TrustZone device then the Boot ROM should lock the protection setting while keeping the page readable.
When read protected, reads of this space generate a bus error, return data of all 1’s and do not report SEC/DED ECC or Parity errors. Internal sources such as CRC and FLT are blocked (via return data of all 1’s) w/o generation of an access error.
Local Lock Bits
The user may optionally select to prevent further writes to a CRP register bits by also setting associated local LOCK bits (in the same register) when writing the CRP value.
When a local lock bit is set (BCnRPLOCK = 1, n = 1 or 2), subsequent writes to that register (even if the unlock sequence is followed) have no effect, creating a “write once’ register. Local LOCK bits revert to the unlocked state at reset.
VSS Page Protect
For device that have an CAM option and a TrustZone CPU, the FCR is a secure peripheral with access to secure memory regions. CRC and FLT feature are available for these regions as long as the CRP register allows reads to them.