Memory readback protection on the nrf5340

[kpreiss]

Hi,

What is the process for locking the app and network cores on the nrf5340 from allowing someone to read the internal flash memories using a debugger via SWD?  Then what would be the process for "unlocking" the part should we want to reprogram it.

Thanks.

[kpreiss]

We would like to accomplish the locking and unlocking using the Segger JLINK debugger running the "jlink" command line program.

[Raoul]

Hi,

This is controlled by the Control Access Port, please take a look at this documentation page: https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf5340%2Fctrl-ap.html&cp=3_0_0_7_9

and this related question on DevZone:  nRF5340 NVS and readback_protection

Best regards,

Raoul

[kpreiss]

Does this mean that if the DEBUG port is locked, the micro flash can never be programmed again using the debugger?

[Raoul]

Not at all, you can always recover the device by performing an ERASEALL, after which the debug access port is opened. The only consequence is that you lose the firmware image on the device. The main purpose of this APProtect is to prevent unwanted firmware readout of devices in the field.

In practice, when you encounter a locked device in NCS (through for example the VS Code extension), you'll have to option to perform a "recover" operation, which erases all firmware ("ERASEALL") and opens the access port. Then, when you flash new firmware to the device, this firmware can be configured to keep the debug access port open (useful during development) or let it remain closed (which is strongly recommended for production).

This blog post has more information on the new "hardened" access port protection, which can also be found in the nRF5340:  Working with the nRF52 Series' improved APPROTECT

Best regards,

Raoul

[kpreiss]

Thank you.  Perfect.