Downgrade your iPhone DFU mode


My iPhone crapped out on me this weekend. I went to use it and the screen wouldn’t show at all. I loaded iTunes which was able to recognize it and offer to restore it to factory. Word of advice, iTunes is very sneaky! I didn’t realize that the factory restore it offered came with a complimentary upgrade to OS 3.1.2! It became apparent after I went to use the device and swiped right revealing the new spotlight search. Crap! I needed to keep it on 2.2 because I need to verify 2.2 compatibility. No worries, I’l just down grade when I get to the office. I then realized that I couldn’t build and run on device using XCode. I was getting “No Provisioned device connected” errors. I got concerned thinking I had to go through the whole re-provisioning my device hassle. Then I realized the “use for development” button in XCode. One thing lead to another then I finally realized all of the ugly truths about iPhone development.

1. OS 3.1.2 only accepts builds from XCode with iPhone SDK 3.1.2.
2. The iPhone SDK 3.1.2 only installs on OSX 10.6 (Snow Leopard)
3. Apple no longer offers any iPhone OS earlier than 3.1.2 on its website.
4. If you are lucky enough to find a lingering copy of iPhone OS 3.0 or earlier, you cannot roll back from 3.1.2 (…easily) due to baseband errors.
5. DFU mode is not easy to do or understand.
6. You will likely spend the good part of a couple of days trying to recover from an unintentional upgrade as your first 5-7 rollbacks will leave you with misc errors.

The simple answer is that you cannot downgrade the OS without using DFU mode. DFU stands for Device Firmware Upgrade and is a secret mode that Apple doesn’t want you to know about. You have to use something similar to the old Nintendo Contra cheat (you remember up, up, down, down, left, right, left, right, b, a…) to enable it. I’ve tried it a couple of times so far and realized that you probably should have a completely installed OS before trying it. My second attempt (after a fresh iTunes restore) left me with an error and I’m hoping the third time is a charm. Here goes nothing…