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's 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 solutions that use 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 SARAM 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 could 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. Figure 5-3 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.