AN4240 datasheet(14/30 Pages) STMICROELECTRONICS

14 / 30 page

Application code structure

AN4240

14/30

Doc ID024209 Rev 2

The second application code configuress the device in order to:

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Add in the ctr0.ppc file the code size and the start address of the code to be secured

•

Add in the locator file the reserved section needed to release the secure boot

•

Reset the device two times in order to issue Secure Boot OK, as described in the

Secure boot procedure Figure 5.

Finally the third application code configures the device in order to:

•

Issue a CSE BOOT OK command to verify if the content of the flash is not modified

•

Issue an encryption ECB and a CBC command over a preloaded figure (ST Logo)

•

Issue a decryption ECB and a CBC command over the encrypted figure to show the

plain text figure again

5.2.1

Disable Software Watchdog

This function allows disabling the Software Watchdog using a key word and permit the

access to the control register of the SWT module.

The SWT is disabled in order to avoid the period execution of watchdog service that could

issue a system reset:

Figure 6. Software Watchdog disable function

5.2.2

Mode Init

This function allows to configure the mode entry of the device in order to turn on all the

peripherals considering the right dividers for a system clock of 120 MHz.

AN4240 Datasheet(PDF) 14 Page - STMicroelectronics