ST X-CUBE-SBSFU, Руководство пользователя, Страница: 65 / 94

UM2262 Rev 6 65/94
UM2262 Secure Engine protected environment
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Figure 35. SBSFU requesting a Secure Engine service
The SE call gate mechanism uses the concepts described in Section A.1.1: SE core call
gate mechanism to provide a unique entry point to the Secure Engine services. The
difference with Section A.1.1 is that the MPU protection replaces the Firewall protection; the
constraints for the placement of the call gate code are only the MPU region constraints (the
call gate must be located in the privileged code region).
When the Secure Engine processing ends, the call gate concept provides a single exit point
and the SVC call return sequence applies. This return sequence brings the software back to
the unprivileged level of execution. Then, any further direct access to the Secure Engine
code and data generates an MPU fault.
The Secure Engine service exit is described in Figure 36 .