Hello,
We already use the AJSM module to lock the JTAG port on our controllers, but some customers are worried that a 128bit key is not very secure.
I would like to know if there is a way to lock the JTAG port permanently in a way it cannot be unlocked anymore.
Thanks,
Martin
I think in the TMS320, when you wrote all 0 in the key you could not unlock anymore.
Section 6.22.7 Advanced JTAG Security Module of TMS570LC4357 Hercules
Microcontroller Based on the ARM® Cortex®-R Core datasheet (Rev. C) contains:
A user can secure the device by changing at least 1 bit in the visible unlock code from 1 to 0. Changing a 0 to 1 is not possible because the visible unlock code is stored in the One Time Programmable (OTP) flash region. Also, changing all 128 bits to zeros is not a valid condition and will permanently secure the device.
I haven't tested that.
