The following are the typical situations under which unsecuring can be required:
- Code development using debuggers (such as Code Composer Studio). 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 in order to unlock the device to enable programming. 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 3-22 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.