topic Read trim value after Secure in 8-bit Microcontrollers

Read trim value after Secure

Stipey75 — Thu, 15 Mar 2012 16:10:02 GMT

Hi!

Maybe it's a stupid question, I think answer is no, but maybe you guys could surpise me!

I am using an AC32 with freescale bootloader and my application code, the device i secured but we didn't have set the backdoor feature!

Is there any way to read the trim byt before erasing the device, we suspect that the device is not correctly programmed by our supplier...

Thanks !

Re: Read trim value after Secure

kef — Fri, 16 Mar 2012 00:35:32 GMT

Flash, RAM and EEPROM are secure resources. Peripheral registers, including TRIM bits in ICGTRIM register, are never secured and are always readable over BDM. So it is possible, but may depend on tools you are using.

Don't know how to do it on CW10, but with CW6.3 and USB Multilink, you can start debug session, BUT instead of hitting [[Connect (Reset)]] button, you should click [[Hotsync]] button. Then you should navigate memory component to address of trim register and read it. MCU should keep running your code, which should guarantee you, that your program started executing and copied trim bits from NVTRIM locations in flash to trim registers. Just tried it with QE128 and CW6.3.

Re: Read trim value after Secure

Stipey75 — Fri, 16 Mar 2012 16:44:22 GMT

Thanks for you answer kef!

I solved programming via bootloader the application with a little modify to send in serial the trim value (so i didn't touch the original).

Your suggestions is quicker anyway..i thought that I cannot read trim value with secured device!!

Re: Read trim value after Secure

bigmac — Sat, 17 Mar 2012 06:23:16 GMT

Hello,

If it is possible to use the serial bootloader, at the correct baud rate, this would seem to imply that the trim value must be currently correct. It is equally important for the bootloader initialisation code to read the non-volatile trim value, and write this to the trim register.

I presume that the only issue is whether the non-volatile trim setting has been correctly calibrated during the programming of the bootloader code, so as to provide the required internal reference frequency.

With a secured device, you will not be able to directly read the non-volatile setting, using the BDM, but the trim register itself should be readable.

Regards,

Mac