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12.4.17. Operating System Lock Access Register

The OSLAR is a write-only register that locks the debug registers so that the APB interface returns a slave-generated error response for accesses to locked registers. This is useful for the OS to interrupt the debug session cleanly when it wants to save the state of the debug registers.

Figure 12.14 shows the bit arrangement of the OS Lock Access Register.

Figure 12.14. OS Lock Access Register format

Figure 12.14. OS Lock Access Register format

Table 12.27 shows how the bit values correspond with the OS Lock Access Register functions.

Table 12.27. OS Lock Access Register bit functions


OS lock access

OS lock access. Writing a 0xC5ACCE55 key locks the debug registers. Access to locked registers returns a slave-generated error response. To unlock the registers, write any other value.


Writing the key also resets the Operating System Save and Restore Register (OSSRR) sequence to the beginning.