TCU firmware downgrade

Yes, I upgraded to 3.4.22251, and did a master reset. When I check SiriusSM in Apps, it only says Audio is Subscribed, all other services (including Traffic) are Not Available, I did have 3 months trail which will end next Jan, anyway, I’m going to wait few days and see if it will show up.

Back to the TCU topic. I checked the TCU data service on ATT website with donor VIN, looks like I can have 3 months trials, so I decided to give it a try. I upgraded APIM firmware to 3.2/3.3 per the instructions from F150chief (Thanks again!), and after upgrade, there are some AS build checksum errors, I loaded the default configuration the errors are gone. Now the WiFi hotspot shows up on Sync, and I’m able to change SSID and password.

My question is: is AS build part of firmware or not? probably not I guess, if that is the case, how do I know if my old AS build data can work normally with new firmware? is the new firmware backwards compatible with old AS build data? if not, do I need to manually change the AS build data to make sure it will work with new firmware?

There are 3 parts to the module programming:
Firmware is the base level instruction set for the module hardware, in the strictest sense.
Software is the module interface for HMI and other functional interfaces, like networking, etc.
Asbuilt Data is the option or feature set for both firmware and software, or either depending on the module.

Firmware and software changes over the life of the module or program. This is due to updates, features, etc. It is important to understand that this makes the asbuilt data change accordingly along with the changes to the firmware or software. In some cases, like the TCU’s, the asbuilt changes in accordance with the features changed or added in the TCU firmware. This is natural and to be expected. The good thing is that 99% of the time the old asbuilt data is still valid, even if there are additions to the feature set for the asbuilt. Usually the new data lines will just be ‘0’ or null, so no issues arise with the older data.

As a general rule, you should always reload the asbuilt data whenever any change to the firmware is made. This is due to firmware changes that may affect instruction addresses and such. Make it a practice to do so.

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