You currently have TXE 1.x firmware which is Bay Trail so TXE 2.x (Braswell, Cherry Trail) is not relevant. Since you have TXE 1.x firmware you can update to latter 1.x releases only. If you check the TXE thread > Section B > TXE 1.x Upgradeability, you will see that unless your Flash Descriptor is unlocked, you cannot upgrade to anything after 1.0.x using FWUpdate even though the latest compatible firmware is indeed 1.2.x. To check if your flash descriptor is unlocked, run Flash Programming Tool with the command fptw -dumplock. If you see 00 00 FF FF for both CPU and TXE then you have an unlocked descriptor and thus can (after some hoops, not with FWUpdate) update to the latest TXE 1.x firmware which is the one you run through MEA. If the descriptor is locked and you want to unlock it, the easiest thing to do is to use a cheap programmer. The other method requires shorting two pins of the audio chip while the system boots to temporarily disable the flash descriptor protection and thus allow TXE read/write access. The HMRFPO message you mentioned is only relevant if the OEM has implemeted it at the BIOS, usually by an option such as ME Disable, ME Reflash Enable/Disable and so on.

Contrary to ME or TXE 2.x, TXE 1.x was very complicated for no reason. To explain: TXE 1.x had two firmware releases based on Platform, Mobile/Desktop (M/D) or Tablet/IVI (T/I). For each platform (M/D or I/T) the SKUs change according to minor version.

* TXE 1.0 had two SKUs: 1.25MB and 3MB. If you have 1.25MB you upgrade to a latter 1.25MB and if you have 3MB you upgrade to a latter 3MB.
* TXE 1.1 merged those two SKUs into one: 1.375MB which fully supplements/replaces both the older 1.25MB and 3MB SKUs.
* TXE 1.2 is the same as 1.1, meaning one 1.375MB SKU which suplements/replaces both 1.1 and 1.0 SKUs.

In theory you can upgrade from 1.0 all the way to 1.2 firmware no matter if your current 1.0 SKU is 1.25MB or 3MB. Same for 1.1 to 1.2 upgrade, very much possible. The problem is, to upgrade from one minor version to another, the full TXE region needs to be reflashed which requires an unlocked flash descriptor which in turns grants full read/write access to the whole TXE region. FWUpdate updates the TXE partially (where it counts, meaning CODE/Version) and does not need the flash descriptor to be unlocked. So it's only usable to update within a specific minor version, either 1.0, 1.1 or 1.2.

You currently have 1.0 firmware. I don't know what SKU you have (1.25MB or 3MB) as ASUS doesn't include the TXE region at their BIOS images and so I cannot check with MEA. Try running TXEInfo -verbose and TXEManuf -verbose, hopefully one or the other will mention the SKU somewhere. I also don't know what firmware platform your system has, M/D or I/T. However, it's almost always M/D even at Tablet systems, I don't know what Intel was thinking honestly.

As far as upgradability is concerned, you have two options. If your flash descriptor is locked then you can only update via FWUpdate to latter 1.0 firmware, either 1.25MB or 3MB based on what your system is using. If it's unlocked you can upgrade to the latest 1.2 firmware (1.375MB) by Flash Programming Tool (FPT). I need to give more details for the 2nd case but only if indeed your flash descriptor is unlocked or you plan to use a programmer. I have mentioned how to determine the lock state of the flash descriptor at my previous reply.

For example:

--> If I assume you have a) M/D firmware , b) 1.0 current firmware , c) 1.25MB SKU for 1.0 , d) Locked flash descriptor: FWUpdate with "Intel TXE 1.0 1.25MB Firmware v1.0.5.1120 BYT-M/D"

--> If I assume you have a) M/D firmware , b) 1.1 current firmware (1.375MB) , c) Locked flash descriptor: FWUpdate with "Intel TXE 1.1 1.375MB Firmware v1.1.4.1145 BYT-M/D"

--> If I assume you have a) M/D firmware , b) 1.0 current firmware , c) 1.25MB or 3MB SKU for 1.0 , d) Unlocked flash descriptor: FPT+FITC with "Intel TXE 1.2 1.375MB Firmware v1.2.1.1153 BYT-M/D"

Ok, it's impressively stupid of me to have forgotten such an easy thing. Run FWUpdate -save txe.bin command. Attach it here or input it at MEA, it should tell you what platform (M/D or I/T) and SKU you currently have (1.25MB or 3MB). Complete brain fart on my part...

Also, you can use the latest v1.x tools as provided at the TXE thread. They are fully compatible with 1.0 firmware releases.

Those tools and documentation are part of the System Tools packages as they are called. Since I search for these as well, you can find the latest at the TXE thread (section C), both tools and documentation.

As you correctly read, the remaining SPI space is taken by the TXE region. If for example that remaining space is 6MB, then no matter the SKU, it will be 6MB. You can find 1.25MB firmware at a TXE region of 6MB, it doesn't have to be 3MB. Generally, don't trust size but actual SKU as analysed from the firmware image when run through MEA.

You have 1.0 firmware, 3MB M/D and a locked flash descriptor so your only option is to use FWUpdate with Intel TXE 1.0 3MB Firmware v1.0.7.1133 BYT-M/D. If at some point you decide to unlock the flash descriptor or similar you could upgrade to 1.2.x via FITC+FPT but for now only what I said above.

FWUpdate (FWUpdLcl.exe) and not Flash Programming Tool (fptw.exe). Completely different tools. If the flash descriptor was not locked and you accepted, you could have bricked the system. In this case, if you had accepted, it would have shown Error 26, no CPU access to the TXE region due to the locked flash descriptor but that doesn't mean that the initial tool choice was correct in any way.

Great. It's not really needed in your case but as an extra step you can also run fptw -greset command to reset the TXE for good measure. After the reset, make sure to also run TXEInfo (no red errors) and TXEManuf (green "TXEManuf Operation Passed") in order to verify that everything is alright as far as TXE health is concerned.