The following are the typical situations under which unsecuring 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. The Flash utilities can disable the code security logic in new devices without any authorization, since new devices come with an erased Flash. However, reprogramming devices that already contain a custom password require the password to be supplied to the Flash utilities to unlock the device to enable programming. In custom programming 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 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. Figure 3-16 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.