Firewall (FW) RM0351
122/1693 DocID024597 Rev 3
4.3 Firewall functional description
4.3.1 Firewall AMBA bus snoop
The Firewall peripheral is snooping the AMBA buses on which the memories (volatile and
non-volatile) are connected. A global architecture view is illustrated in Figure 5.
Figure 5. STM32L4x6 firewall connection schematics
4.3.2 Functional requirements
There are several requirements to guaranty the highest security level by the application
code/data which needs to be protected by the Firewall and to avoid unwanted Firewall alarm
(reset generation).
Debug consideration
In debug mode, if the Firewall is opened, the accesses by the debugger to the protected
segments are not blocked. For this reason, the Read out level 2 protection must be active in
conjunction with the Firewall implementation.
If the debug is needed, it is possible to proceed in the following way:
• A dummy code having the same API as the protected code may be developed during
the development phase of the final user code. This dummy code may send back
coherent answers (in terms of function and potentially timing if needed), as the
protected code should do in production phase.
• In the development phase, the protected code can be given to the customer-end under
NDA agreement and its software can be developed in level 0 protection. The customer-
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