[FAQ] AM625: [AM625 / AM623] - VPP use case ( Extended OTP and Customer (Security) Keys programming)

Hello Pedro,

Thank you for the query.

Pedro Santos said:

Is VPP required to write no any fuse, or only to write to the ones associated wtih the secure boot feature?

The question is not clear.

I assume the question is is VPP required to program any eFuse bits?

The answer is yes,

Pedro Santos said:

Background of my questions: We have a board with AM62 and we want to evaluate if our customers can write to the fuses ONLY at manufacturing, or also in production (which we know it's complicated, but is it even feasible)? 

This should be feasible if customer has On-board VPP supply and the required controls to enable the VPP to program the eFuse.

Pedro Santos said:

From question 8, we have this phrase: "An OTP (One Time Programmable) Keywriter (software tool) is used to program the eFuse." - This means that no VPP is used after first and only time in manufacturing line? 

I need you to elaborate the query. Is the question related to the key writer?

Regards,

Sreenivasa

Hello Pedro,

The below link should help.

https://software-dl.ti.com/tisci/esd/latest/2_tisci_msgs/index.html

Pls look for extended OTP and OTP keywriter.

Regards,

Sreenivasa

Hi Kallikuppa, thanks for your help!  

Let me rephrase my questions a little bit to make sure I got everything: 

- I understood that in order to use efuses, we always need VPP voltage. So can I conclude that to use ANY fuse in secure boot, I must provide VPP voltage? There is no way in software to change secure boot fuses?

Hello Pedro,

Additional inputs on the OTP access:

The TIFS core only has the access to the Extended OTP. The other cores can read the Extended OTP with the following TISCI message:

https://software-dl.ti.com/tisci/esd/latest/2_tisci_msgs/security/extended_otp.html?highlight=otp#sec-api-ext-otp-read-otp-mmr

Regards,

Sreenivasa