G988U and G988U1 Firmware Links and Flashing Discussion Here

For those who aren't already aware, G988U is the model number of all of the US carrier versions of the S20 Ultra. The G988U1 is the model number of the same device, but sold by Samsung SIM unlocked and with no carrier bloatware. Firmware is 100% interchangeable among these models: any U or U1 firmware version can be flashed to any U or U1 device at any time, assuming that you're not trying to downgrade the bootloader. Also, U firmware is identical for the 4 base files (AP, BL, CP, CSC) for each individual build, no matter which carrier it comes from. So if you download 2 different carrier versions of the exact same build, the 4 base files will be identical. Where the firmware differs is in the USERDATA file - that's where the carrier bloatware and customizations reside.

Manual Odin flashing is designed for those who:

- want to manually update to a newer version of U firmware on their U device, either because they don't want to wait for their carrier's OTA or because OTAs aren't working on their device, or a different carrier got a new feature/patch before they did
- want to flash U1 firmware to their U device
- want to convert from U1 firmware to carrier U firmware
- want to convert from one carrier's U firmware (with all apps and bloatware) to a different carrier's U firmware (with all apps and bloatware)

For those who aren't already aware, anyone can now download firmware for almost any Samsung device any time that they want, via SamFirm or Frija. There are threads and info about them here on XDA so I won't waste time explaining - do a search if you're not already familiar with these tools. But they only provide whatever the latest/newest/current version is - nothing older. I pay for a subscription to a site that gets the official releases (usually) before they hit SamFirm/Frija, so that's where my files come from. However, I don't have unlimited bandwidth on the site, and it's also quite time consuming to download the files, zip them up, and upload them to AFH. And, I do threads like this for every single Sx and Note x model - so I won't be uploading every single version. The only full builds that I upload are ones where I get access to a new bootloader and/or Android version early, before they hit SamFirm/Frija.

This is not a "beginner's guide to Odin flashing" -type post/thread, so I won't list basic, step-by-step flashing instructions. My threads are geared towards those who already know what they're doing. If you're new to manually flashing Samsung firmware, I recommend you consult one of those "beginner's" guides- there are tons of them here on XDA.

Happy flashing!

U firmware: https://www.androidfilehost.com/?w=files&flid=305574
U1 firmware: https://www.androidfilehost.com/?w=files&flid=305575

Notes:

- DON'T QUOTE THE OP WHEN YOU REPLY, kthx

- I have lots of threads just like this one for other Samsung flagships, if it interests you. For those who have already made use of my previous threads for a different device and are upgrading to an S20, welcome back

- My zips are compressed extra small for space and bandwidth savings. The default Windows extractor can't handle it, so you'll need a 3rd party tool like 7zip, WinRAR, etc

- My naming method for folders on AFH is: build - bootloader - Android version
So "SAT - 1 - 9.0" means the full build number ends in SAT, it's bootloader version 1, and it's Android 9.0. When bootloader and Android versions increment, the first build to have those changes will have its folder notated appropriately.

- HOME CSC file keeps data intact; using the other CSC will wipe data. Flashing USERDATA will also wipe data

- Since AT&T doesn't allow their firmware to be publicly available (for any of their devices), I'll try to always upload at least one USERDATA per bootloader increment for AT&T (and Cricket, if they get this model). I'll also upload any full builds if AT&T is the only carrier to get that specific build, because you won't be able to find the files anywhere else.

- For identifying USERDATAS, and to know what region/CSC to use in SamFirm/Frija:

ATT = AT&T (not available via SamFirm/Frija)
CCT = Xfinity Mobile (Comcast)
CHA = Spectrum Mobile (Charter)
SPR = Sprint
TMB = T-Mobile
USC = US Cellular
VZW = Verizon (available via SamFirm/Frija, but Manual Entry is required - Auto will not work)
XAA = U1 firmware

- the correct procedure for switching from one carrier's firmware to another is:
1. Flash full U1 firmware package including non HOME CSC
2. Upon boot, insert a SIM of the carrier whose firmware you want
3. Watch for the popup that says "reboot to apply new carrier settings" etc, and do it
4. After that restart completes, reboot back to Download mode and flash the full U firmware package, with the USERDATA file of the carrier whose firmware you want

SyCoREAPER said:

Interesting. Flashing the U CSC is all that's needed? Any OTA issues?

Sorry for delay
No.... If you do U1 ( or in my experience anything besides basic original firmware) then no OTA. BUT at least calling features can work

jcrompton said:

@iBowToAndroid Just curious -- when flashing ATT, for example if you wanted to go back to the original completely stock ATT firmware , is it even completely possible? Are the TMB and USC firmware downloads the same minus the ATT userdata? If the USC and TMB or XAS (those are the ones I saw) aren't the same then which is the best one for flashing an ATT branded phone?? Thanks

Click to expand...

All those answers are already in the OP.

1. Yes it's possible

2. Yes they're the same

3. Best one for flashing ATT firmware is ATT files

Shuthefrontdoor said:

Thanks, would I need to flash userdata?

Nope. USERDATA only exists on U firmware

itchyUnder said:

In Odin, there are 4 components to flash, including the csc or home csc. I am wanting to flash the u1 unbloated version but use the branded csc to keep the carrier features.

All U firmware pieces are identical, for each build - no matter which carrier it's from. So there is no such thing as an "AT&T CSC". So you can flash the CSC from any released build of Android 11 U firmware, combined with the rest of the files from any released build of Android 11 U1 firmware.

Just wanted to say a couple things. First, thanks for the work the OP and others have put in making this info and the ROM's available!

Second, it's been a while since I've flashed a ROM so I was a little rusty, here's a couple tips that may help others. There's no power button, obviously. Volume down and Bixby key force power off. Volume up and Bixby key boot the phone into recovery mode. At one point I ended up with a failed copy to the phone from Odin that horked things up, got a checksum failure. At that point Odin wouldn't download any of the images. I used the patched version of Odin (several threads with it easily searchable on XDA). The patched version fixed it (I think it bypasses some of the safety checks) and I was good to go again.

Like some others, I was having trouble getting the carrier firmware to stick, I kept ending up with XAA after flashing the carrier stuff, including that AT&T folder. It was driving me nuts. I'm on Firstnet and I got thinking that may be the issue, since it's got lots of quirks. I'm guessing the Firstnet SIM wasn't triggering whatever the firmware needed to see in order to install that AT&T version (even though it's basically AT&T although Firstnet has a separate network core from AT&T).

I tried popping in a Verizon SIM I had and that triggered the install of all the Vz crap and it all worked as expected. So knowing that the process worked but just wasn't working right with Firstnet, I ordered a couple AT&T sim cards. I reflashed and then inserted the AT&T sim and it triggered the carrier update and then successfully flashed the AT&T firmware. I was also stoked that it worked with an unprovisioned sim card, I was hoping that would work and I wouldn't have to sign up for service just to flash my phone.

After this I popped in my Firstnet sim and everything's been working perfectly. I'll also note that for those on Firstnet and are subscriber paid, you can login to the admin portal and manually update your device IMEI yourself. Even after I had my sim in my new phone it was still showing my old phone until I manually updated the IMEI in the portal. I'm guessing you're not going to get all the features without updating that.

So, after all that, on Firstnet, with AT&T firmware and my IMEI number updated, I'm getting all features working, VoLTE, Wifi Calling, etc. I'm super happy with it and also am seeing a large increase in speeds over running on the XAA firmware. I'm guessing on XAA I'm either not getting CA or Priority, or both. I'm seeing about triple the speed on the carrier firmware. YMMV since Firstnet is a unique beast but wanted to throw my experience out there in case it helps anyone else.