Using Apple Configurator, you can now downgrade T2 BridgeOS Beta to a Production version of BridgeOS.
Downgrading the version of your T2 BridgeOS has never been possible. Developers and customers could only get a NEWER version of BridgeOS when updating or upgrading macOS. The ability to downgrade BridgeOS on a T2 Mac was simply not possible. This new change to Apple Configurator 2 most likely happened between version 2.12 – 2.12.1.
Table of Contents
- 1. Why would you want to downgrade from a beta version of BridgeOS?
- 2. Can you Downgrade to a Lower Production version of BridgeOS?
- 3. Problems Running Catalina with a Big Sur Beta BridgeOS Version.
- 4. Closer look at BridgeOS versioning
- 5. The Big Sur installer is now using DeviceIDs compatibility checks.
- 6. BridgeOSUpdateCustomer updater
- 7. How to Downgrade a Beta Version of BridgeOS to a Production Version.
- 8. The Revive Option (for science)
- 9. Final Notes
1. Why would you want to downgrade from a beta version of BridgeOS?
Let’s say that you installed Big Sur Beta 6, and are now having a ton of problems. You probably want to downgrade to Catalina so you can work again. The only problem is, you are still on Big Sur Beta 6 BridgeOS version 18.16.12370. Keep in mind, your Mac SHOULD still work fine with this version. An example of this is if you have Catalina 10.15.6 installed on your Mac, your BridgeOS version is 17.16.16610. Let’s say that you need to test something on version 10.15.3. After installing Catalina 10.15.3, your BridgeOS version will NOT be downgraded to the period correct version of 17.16.13050. It will run just fine on the 10.15.6 version of 17.16.16610 BridgeOS. The same is the case if you have a Big Sur Beta version of BridgeOS and you downgrade to Catalina.
2. Can you Downgrade to a Lower Production version of BridgeOS?
If you are running macOS Beta, then you can use Apple Configurator 2 to downgrade your T2 BridgeOS to a final or production version of BridgeOS.
What about if you are running a production version of macOS? You can downgrade BridgeOS with Apple Configurator 2, but only for 1 week after a new macOS software update. Apple will unsign the previous version of BridgeOS along with previous iOS updates.
3. Problems Running Catalina with a Big Sur Beta BridgeOS Version.
Let’s say after you downgraded from Big Sur Beta to Catalina 10.15.6, you are now having problems. You might start to see weird issues or crashes? Normally you would have to wait until the next beta or the production version of Big Sur to get a stable version of BridgeOS on your Mac.
How do you even know what the correct version of BridgeOS your Mac should be on? I keep track of all macOS & BridgeOS versions for you here > mrmacintosh.com/macos-system-status-version-info-for-macadmins/
4. Closer look at BridgeOS versioning
Apple Configurator 2 logs are stored in ~/Library/Group Containers/xxxxxxx.group.com.apple.configurator/Library/Logs
For some reason 2.12.1 no longer creates a log, this problem looks like a bug.
The plist containing what BridgeOS ipsw file is used is located at the web address below.
https://mesu.apple.com/assets/bridgeos/com_apple_bridgeOSIPSW/com_apple_bridgeOSIPSW.xml
Looking at the xml file, I need to find my 2019 16″ MacBook Pro. Regular Model Identifiers or BoardIDs are not used here. You need to find the iBridge ProductID
. Below is a snippet of the above .xml
file. Below the version of BridgeOS = 17P6610
iBridge2,14
17P6610
Restore
BuildVersion
17P6610
DocumentationURL
FirmwareSHA1
e9776dda5d2d70e0e0988c18a84b528155b6423b
FirmwareURL
http://updates-http.cdn-apple.com/2020/macos/001-36803-20200810-A97B835C-DB65-11EA-B99D-EC2029ACBA60/iBridge2,1,iBridge2,10,iBridge2,12,iBridge2,14,iBridge2,15,iBridge2,16,iBridge2,19,iBridge2,20,iBridge2,21,iBridge2,22,iBridge2,3,iBridge2,4,iBridge2,5,iBridge2,6,iBridge2,7,iBridge2,8_4.6_17P6610_Restore.ipsw
The iBridge ProductID
= iBridge2,14
I started to keeping track of all the DeviceIDs in my BoardID Database. We can now find iBridge ProductID
= iBridge2,14
below.
mrmacintosh.com/list-of-mac-boardid-deviceid-model-identifiers-machine-models/
iBridge2,14 | J152FAP | 0x3A | Apple T2 MacBookPro16,1 (j152f) |
iBridge2,14
is a 2019 16″ MacBook Pro!5. The Big Sur installer is now using DeviceIDs compatibility checks.
A change to the macOS Installer Beta was noticed by @grahampugh. He noticed that the new Big Sur installer now looks at the Mac DeviceID
for T2 Systems and BoardID
for older 2017 and below Macs.
6. BridgeOSUpdateCustomer updater
Now that we have the DeviceID
, how do we know which version of BridgeOS is compatible for this model? The xml
file gives us a clue BuildVersion
. I am used to keeping track of the BridgeOS Boot Rom version which is listed like this 17.16.16065.
17P6610
The BuildVersion/BuildNumber
is located inside the BridgeOSUpdateCustomer > BridgeOSUpdateCustomer.pkg > BuildManifest.plist.
BuildIdentities
ApBoardID
0x3E
ApChipID
0x8012
ApSecurityDomain
0x01
Info
BuildNumber
17P6610
BuildTrain
bridgeOSJazzGHW
DeviceClass
j214kap
7. How to Downgrade a Beta Version of BridgeOS to a Production Version.
I documented how to restore & revive BridgeOS here > mrmacintosh.com/how-to-restore-bridgeos-on-a-t2-mac-how-to-put-a-mac-into-dfu-mode/
The process to downgrade is basically the same.
Apple Configurator 2 offers two options to Reinstall/Downgrade BridgeOS. Only the Restore
option will help you downgrade and stay on the Catalina specific version.
- Restore = ERASES YOUR HARD DRIVE + Downgrade BridgeOS
- Revive = Actions > Advanced > Revive Device = Downgrade BridgeOS*
If you want to downgrade to macOS Catalina and a Catalina version of BridgeOS, the fastest way is to use the Restore option. Once the restore is complete, you will be on a the Catalina Production Version of BridgeOS and will have empty hard drive. You can now use Internet Recovery to reinstall macOS Catalina.
What happens if you chose the Revive option?
8. The Revive Option (for science)
As noted above, you have no real reason to use this option. But for science, what would happen? If you are on Big Sur Beta want to downgrade T2 BridgeOS Beta using the Revive option, you will leave your Mac in a non bootable state. This is because you are now running a BridgeOS version that is OLDER than the required Big Sur Beta BridgeOS. The good news is, your T2 Mac is smart enough to repair itself! As soon as the revive option finishes, your Mac will boot to a flashing folder alert or the Internet Recovery boot menu. If it boots to the flashing folder, just boot to Command Option R or Command R and you will get the menu below.
Connect to the internet and let it continue. You will be brought to a message that says,
A software update is required to use this startup disk.
Click Update
and your mac will download the correct build of Big Sur Beta BridgeOS.
Once complete, the Mac will boot back to Big Sur. The only way to avoid this would be to boot the Mac to Target Disk Mode so you could erase the drive and reinstall Catalina. That’s why if you want to have BridgeOS and Catalina on the same version the Apple Configurator RESTORE option is the way to go. Just make sure to backup everything before you start as all data will be lost.
9. Final Notes
It should be pretty rare that you should ever need to downgrade BridgeOS from a Beta version. Keep in mind this will ONLY work for beta versions. As I noted above you can’t downgrade from a 10.15.6 version of BridgeOS to say a 10.15.3 version. With that said I would love to be able to downgrade to a previous version. If it’s your job to test OS Updates, once you update one test T2 Mac it’s done. It will not perform the BridgeOS update again until the next update. I really like that Apple let’s us downgrade from a beta version of BridgeOS, the more ways for customers to fix their devices the better! A big hat tip goes out to Mr. Macintosh reader thomas089 for first testing this and commenting in my main article!
Downgrade T2 BridgeOS Beta