My team is looking into disabling the M4 core using the fuses. According to the reference manual (IMX8MDQLQRM), the M4_DISABLE fuse is in the TESTER region. This TESTER region is locked by the TESTER_LOCK by NXP. This means we cannot disable the M4 core after purchasing the IMX8M chip. Is this reasoning correct?
Yes, if the TESTER_LOCK = 0b11, there is no way to set that to 0b00 and the related result is that the M4 core can't be disabled. Actually, if you don't need to use the M-core, there is no necessary to disable it. You could just leave it there unused.
My understanding is you can only transition fuse values from 0 -> 1 and 1 values are permanent and cannot be set back to 0. So there is no way to unlock a locked region. Is that correct?
According to the reference manual, the related fuses in the tester field can be unlocked by setting the first two bits of TESTER_LOCK(0x400) register to 0. And then, you could disable the M4 core by setting M4_DISABLE(0x450) register to 1.
My understanding is that fuse values can only be transitioned from 0 -> 1, and the reverse is not possible. If we receive chips with the TESTER_LOCK = 0b11, then there is no way to set that to 0b00. Is this correct?
Yes, if the TESTER_LOCK = 0b11, there is no way to set that to 0b00 and the related result is that the M4 core can't be disabled. Actually, if you don't need to use the M-core, there is no necessary to disable it. You could just leave it there unused.
