NXP Semiconductors QorIQ LS1012A Reference Manual

10.4.1.7 Speculative accessesBy default, the TZASC performs read or write speculative accesses that means itforwards an AXI transaction address to a slave, before it verifies that the AXI transactionis permitted to read address or write address respectively.The TZASC only permits the transfer of data between its AXI bus interfaces, afterverifying the access that the read or write access is permitted respectively. If theverification fails, then it prevents the transfer of data between the master and slave asDenied AXI transactions describes.You can disable speculative accesses by programming the speculation_control Register.See Speculation Control Register (speculation_control). When speculative accesses aredisabled, the TZASC verifies the permissions of the access before it forwards the accessto the slave. If the TZASC:• Permits the access, it commences an AXI transaction to the slave, and it adds oneclock latency.• Denies the access, it prevents the transfer of data between the master and slave asDenied AXI transactions describes. In this situation, the slave is unaware when theTZASC prevents the master from accessing the slave.NOTEEnabling speculative access is a potential security risk, if thedevice that is being protected reacts to this transaction. Mostdevices do not have to react to this level of access, andspeculative access is much faster than validating the addressbefore issuing the transaction.10.4.1.8 Preventing writes to registers and using secure_boot_lockBy suitably programming lockdown Register, see Lockdown Select Register (lockdown_select), and asserting secure_boot_lock signal makes the following registers read only:• speculation_control Register. See Speculation Control Register (speculation_control).• security_inversion_en Register. See Security Inversion Register (security_inversion_en).• lockdown_range Register. See Lockdown Range Register (lockdown_range).Locking down the region using lockdown_range and lockdown_select registersFunctional descriptionQorIQ LS1012A Reference Manual, Rev. 1, 01/2018466 NXP Semiconductors