The following are the typical situations under which unsecuring the zone can be required:
- Code development using debuggers (such as Code
Composer Studio™ IDE). This is the most common environment during the design
phase of a product.
- Flash programming using TI Flash utilities such
as Code Composer Studio On-Chip Flash Programmer
plug-in or the Uniflash tool. Flash programming is
common during code development and testing. Once
the user supplies the necessary password, the
Flash utilities disable the security logic before
attempting to program the Flash. In custom
programming that uses the Flash API supplied by
TI, unlocking the CSM can be avoided by executing
the Flash programming algorithms from secure
memory.
- Custom environment defined by the application
In addition to the above, access to secure memory contents can be required in situations such as:
- Using the on-chip bootloader to load code or data
into secure SRAM or to erase and program the
Flash.
- Executing code from on-chip unsecure memory and
requiring access to secure memory for the lookup
table. This is not a suggested operating condition
as supplying the password from external code can
compromise code security.
The unsecuring sequence is identical in all the
above situations. This sequence is referred to as
the password match flow (PMF) for simplicity.
Section 5.7.2 explains the sequence of operation that is
required every time the user attempts to unsecure
a particular zone. A code example is listed for
clarity.