The NIDEN, DBGEN, SPIDEN,
and SPNIDEN input signals are either tied off to
some fixed value or controlled by some external device.
If software running on the processor has control over an external
device that drives the authentication signals, it must make the
change using a safe sequence:
- Execute an implementation-specific sequence of instructions
to change the signal value. For example, this might be a single
that writes certain value to a control register in a system peripheral.
- If the prior step involves any memory operation, issue a
- Poll the DBGAUTHSTATUS_EL1 register to check whether
the processor has already detected the changed value of these signals.
This is required because the system might not issue the signal change
to the processor until several cycles after the
DSB instruction completes.
- Issue an
or exception entry or exception return.
The software cannot perform debug or analysis operations that
depend on the new value of the authentication signals until this
procedure is complete. The same rules apply when the debugger has
control of the processor through the Instruction Transfer Register,
EDITR, while in Debug state. The relevant combinations of the DBGEN, NIDEN, SPIDEN,
and SPNIDEN values can be determined by polling