Upon powering up, flash memory is read/write. At some point during the startup phase, the firmware, the bootloader, or maybe even the kernel triggers some mechanism built into the flash chip that write-protects parts or all of flash memory at the hardware level. This write-protection cannot be reversed by software running on the device and can only be reset by removing power to the flash chip. Variations of this mechanism are used in certain Archos devices running the SDE firmware and in some older Android phones. What is this kind of write-protection called? I'm trying to search for chips and devices/SBCs/boards that have it, but my search terms don't turn up many results.
I am not talking specifically about the S-ON/S-OFF thing. That is a variation of the mechanism, but it is more involved with special designs involving the Qualcomm modem.