Booting a P2 off of ROM or OTP PROM or UV-EPROM?

hinv

Does anyone know if this is possible. The main reason is that I don't want that boot code writable or even modifiable by the system, so I can store hash verification functions and the hash of it and other hashes in the boot ROM, and therefore verify the contents of every other bit of storage in the system.
Does anyone know of such a device that P2 (or even P1 for that matter) can boot off of?

Thanks,
Doug

evanh

The old 8-bit parallel bus with a wide address bus, with 32+ pins, no. Best you can do is buy an SPI part with write protect feature. Many of them have a permanent lock option that supposedly can't be unlocked again.
For Prop1, an I2C part instead.

hinv

I found this https://www.analog.com/media/en/technical-documentation/data-sheets/ds28c22.pdf, but how can I be sure that whatever program that loads data from somewhere else in to compare to a hash in this chip is not messed with and bypassing the process altogether if the program isn't in ROM or OTP PROM or UV-EPROM?

evanh

Not something I've concerned myself with. I make the system as open and configurable as possible, In my line, if someone messes with the setup and it goes badly then that's on them.

Safeties are always independent of control. If they also mess with the safeties then that's really on them.

hinv

@evanh said:
The old 8-bit parallel bus with a wide address bus, with 32+ pins, no. Best you can do is buy an SPI part with write protect feature. Many of them have a permanent lock option that supposedly can't be unlocked again.
For Prop1, an I2C part instead.

Thanks! I didn't know such feature existed. I found this:

hinv

@evanh said:
Not something I've concerned myself with. I make the system as open and configurable as possible, In my line, if someone messes with the setup and it goes badly then that's on them.

Safeties are always independent of control. If they also mess with the safeties then that's really on them.

For most things, I would agree, but I just want to make a secure computer that doesn't run anything I haven't explicitly approved to keep important private data.