This will remove everything off your device, except stuff on the sd-card. I take no responsibility if you somehow brick the it ;). You will end up running 2.2.1 unrooted.

This was written for the at&t nexus one. Im not sure if there are any differences for the other one. You should be able to give this a go, and if the radio doesnt work with this stuff, you can always find the right stuff and re flash it.

Backup your shit

I like "SMS Backup & Restore". Thats all i actually bothered with :P

First you need:

  1. Fastboot (zip contains Win/Mac/Linux versions) or from the android sdk

  2. Your Nexus One connected to your computer via the USB cable.

  3. Your phone set with 'USB debugging' under settings->Applications->Development

  4. An unlocked bootloader. (Im not going to cover that, google it)

  5. All these files.



    3. FRF85B (Froyo)



Step 1: To restore your nexus one with the original shipping roms (ERD79)

  1. Have your nexus one plugged in via USB.

  2. Turn phone off.

  3. hold the volume-down button and turn it on. This will take you to the bootloader.

  4. Select fastboot

  5. Get this file

  6. Unzip the folder, from command prompt chdir to it.

  7. use the fastboot app and execute the following

fastboot erase cache
fastboot flash userdata userdata.img
fastboot flash boot boot.img
fastboot flash system system.img
fastboot flash recovery recovery.img
fastboot reboot

Your phone will turn on and boot with version ERD79. It will ask you setup accounts, but i always skip that here.

Experienced users may be using a custom recovery rom, and could skip flashing it, but I've had one fail to verify some of the other updates, so you shouldn't skip this step.

Step 2: Upgrade to ERE27

  1. copy to the sd card and rename it to

  2. Switch off your phone

  3. hold the volume-down button and turn it on. This will take you to the bootloader.

  4. Select Recovery, when the Android robot shows up (also an exclamation mark) press Power and Volume Up at the same time

  5. Select “Apply” and the installation will start. This will take quite a while and you will get another Android robot screen but your phone WILL eventually come back on firmware ERE27 (wiped).

  6. delete on the phones sd-card.

Step 4: FRF85B frf91 frg83

  1. repeat Step 3 with the FRF85B update

  2. repeat Step 3 with the frf91 update

  3. repeat Step 3 with the frg83 update

And thats it, your now running Android Froyo 2.2.1.
Dont forget to setup your networks APN again :P