TMS320F280049: FORCESEC bit in DCSM Z1_CR Register

Hi Julia,

As explained in the device TRM of both F280049 and F28035, FORCESEC bit when written will clear the respective zone CSMKEY registers which will lead to the Zone being secure.

Julia Li said:

I want to check how FORCESEC bit works in DCSM. In F28035, write 1 to FORCESEC bit in Z1_CR Register, will  trigger the ECSL when running with JTAG next time. I wonder if my understanding is correct? Is there any difference in the function of the FORCESEC bit between F280049 and F28035?

Due to the zone becoming secure, The ECSL would be triggered if the JTAG is halted at any of the secure code.

There is no difference between the F280049 and F28035 in terms of FORCESEC definition and behavior.

Julia Li said:

So, if they want to use FORCESEC bit, they need to set this bit to 1 after setting password in DCSM OTP, is this correct? What will happen if write 1 to FORCESEC bit when DCSM OTP is not configured(F280049 is not secured)? Customer find that F280049 device will reset in this case, and they want to know if this is a normal phenomenon? Thanks!

When you say "DCSM OTP is not configured", I think you are meaning to say that the OTP is left in its default values. Please correct me if my understanding is incorrect.

While shipping the parts, TI will load the default passwords in the OTP and none of the secure resources are grabbed by either zone in F280049. If you write 1 to FORCESEC bit, the respective zone will become secure. This condition will lead to a state where the securable memories will become inaccessible which is just the way DCSM works as it is deemed to be an illegal combination. Please refer to the DCSM chapter from the TRM for more details on this.

As for the customer observation, there could be numerous reasons to end up in a reset as the application code may have stumbled upon an inaccessible memory which would have lead the device to undergo a reset which is an expected behavior. FORCESEC is supposed to be used only when the OTPs are configured so that secure resources are allocated to either zones as per the application use case.

Hope this response clears your questions.

Thanks & Regards
Pramod