sotobou
Posts: 1
Joined: Thu Jun 29, 2017 4:46 am

About customer otp settings

Thu Jun 29, 2017 5:26 am

About customer otp settings question.
Https://www.raspberrypi.org/ documentation / hardware / industrial / README.md
Then, it is stated that if you lock otp with the following command, the area becomes unwritable.
"It is possible to lock the OTP changes to avoid them being edited again. This can be done using a special argument with the OTP write mailbox"
Is it possible to read even after locking?
Immediately after the above document, "Once locked, none of the customer OTP values can be accessed." Is stated but can you read? Or is it impossible to read?
Which is it?

W. H. Heydt
Posts: 11015
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: About customer otp settings

Thu Jun 29, 2017 4:37 pm

sotobou wrote:About customer otp settings question.
Https://www.raspberrypi.org/ documentation / hardware / industrial / README.md
Then, it is stated that if you lock otp with the following command, the area becomes unwritable.
"It is possible to lock the OTP changes to avoid them being edited again. This can be done using a special argument with the OTP write mailbox"
Is it possible to read even after locking?
Immediately after the above document, "Once locked, none of the customer OTP values can be accessed." Is stated but can you read? Or is it impossible to read?
Which is it?
There are things that *have* to be able to read the OTP bits. Granted, they're in the chip itself, but still. Sounds to me like this process is just setting Yet Another OTP Bit (hence, not being reversible) and shouldn't interfere with reading the OTP data. You could, of course, try it and see...set the No Write bit on a CM3L (cost: $25) and then try to read some OTP data. Note also that if this works on a CM3, it should also work on the Pi2B2 and Pi3B as well.

Edit to add... The last line is, I will grant, ambiguous with regard to reading.

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