nRF54L15: OTP region in RRAMC remains erasable (NCS v3.2.0)

[zwq]

Hi Nordic Support Team,

Environment:

• SDK: NCS v3.2.0

• Hardware: nRF54L15

• Driver: nrfx_rramc

Problem Description:
I am currently working with the OTP (One-Time Programmable) region of the nRF54L15 using the provided RRAMC APIs: nrfx_rramc_otp_word_read and nrfx_rramc_otp_word_write.

According to the definition of "OTP", I expected that once a word is written to this region, it should be permanent and impossible to erase. However, during my tests, I found that the data in the OTP region can still be erased (for example, via a debugger ERASEALL command or specific erase operations).

Questions:

1. Why is the OTP region in nRF54L15 still erasable even after being programmed?

2. Is there a specific configuration or UICR register (like APPROTECT or SECUREAPPROTECT) that I must set to make the OTP region truly "One-Time Programmable" and non-erasable?

3. Is this "OTP" behavior implemented purely in software/logic, or is there a hardware-level lock I should be aware of?

Best regards,

---

[Susheel Nuguru]

Hi,

I see the confusion, the OTP region is in the UIICR is write once per Erase all cycle, it is not a permanent fuse into the memory. We should make that clear in the documentation. Nordic solutions does not support an irreversible memory writes at all conditions. The chip still can be erased if they get debug access to the chip. If you lock the debug access using APPROTECT/SECUREAPPPROTECT then no one can erase the chip. These two features combined should give you a proper OTP like feature.

[Susheel Nuguru]

ah, did not see Emil already replied with a really good answer before I replied. 

[zwq]

Thanks for clarifying the relationship between OTP and ERASEALL. It helps a lot for our security implementation on nRF54L15!