BCB, BootCnt, and the bootdata partition

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Maybe some of you guys have figured this out already but it's probably important to note for people developing custom recovery or boot ROMs.

There is a partition on the internal flash named "bootdata" that stores a files named BCB and BootCnt. The secure bootloader updates BootCnt on every non-sdcard boot and if it gets too high it will automatically boot into the recovery partition instead of the boot partition. So, if you're making any custom ROM to be run from the internal flash then you'll want to reset that file in a boot script somewhere. The shell command "dd if=/dev/zero of=/bootdata/BootCnt bs=1 count=4" would do it (Assuming you've mounted the bootdata partition )

The BCB file is similar in that if the secure bootloader boots into the recovery partition for any reason, it will write to that file and will always boot into the recovery partition until that file is cleared. The shell command to clear that file is "dd if=/dev/zero of=/bootdata/BCB bs=1 count=1088"

The bootdata partition just contains a standard vfat filesystem so you just mount it normally.

And for the love of your god do not delete those files! If you do then booting from internal memory will continue to boot into the recovery partition until they are replaced. You would be able to boot from an SD card to replace them though.

Originally Posted by bauwks

Maybe some of you guys have figured this out already but it's probably important to note for people developing custom recovery or boot ROMs.

There is a partition on the internal flash named "bootdata" that stores a files named BCB and BootCnt. The secure bootloader updates BootCnt on every non-sdcard boot and if it gets too high it will automatically boot into the recovery partition instead of the boot partition. So, if you're making any custom ROM to be run from the internal flash then you'll want to reset that file in a boot script somewhere. The shell command "dd if=/dev/zero of=/bootdata/BootCnt bs=1 count=4" would do it (Assuming you've mounted the bootdata partition )

The BCB file is similar in that if the secure bootloader boots into the recovery partition for any reason, it will write to that file and will always boot into the recovery partition until that file is cleared. The shell command to clear that file is "dd if=/dev/zero of=/bootdata/BCB bs=1 count=1088"

The bootdata partition just contains a standard vfat filesystem so you just mount it normally.

And for the love of your god do not delete those files! If you do then booting from internal memory will continue to boot into the recovery partition until they are replaced. You would be able to boot from an SD card to replace them though.

Yup. On the NookColor these had the same functions. Lived on /rom instead of /bootdata however.

Note: My CWM image doesn't probably handle BCB or bootcnt yet (I do in my CM9 image but that is another thing )

Originally Posted by nemith

Yup. On the NookColor these had the same functions. Lived on /rom instead of /bootdata however.

Note: My CWM image doesn't probably handle BCB or bootcnt yet (I do in my CM9 image but that is another thing )

My Ubuntu image does not mount this partition.

Originally Posted by bauwks

Maybe some of you guys have figured this out already but it's probably important to note for people developing custom recovery or boot ROMs.

And for the love of your god do not delete those files! If you do then booting from internal memory will continue to boot into the recovery partition until they are replaced. You would be able to boot from an SD card to replace them though.

Yep-- this is all taken care of in cm9

Update: I don't think you mentioned, but for completeness, there's also the serial file in /rom at devconf/DeviceId that will trigger a rom reformat if it goes missing. there are also some edge conditions that will trigger recovery/flashing such as the presence of certain update.zip files on SD. Also SD boots are treated differently by default, don't increase the boot count, etc. In short, this is very similar to how NookColor works with the added disadvantage of having to deal with, rather than simply ignore or remove, these various "go to recovery' conditions.

I can verify that Bauwks script works and allows internal booting without a bootloop.

Nemith, if you find the time can you add something like this to your CWM recovery.img? I think just adding the /bootdata mount and dd calls to the init.rc file should work. I was going to build my own CWM .img but figured you already had the source code handy.

I'de like to dabble in a CM7 port soon, while CM9 and Ubuntu ports are in-work

Thanks for all your hard work guys!

CWM recovery bootloop

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Originally Posted by bauwks

And for the love of your god do not delete those files! If you do then booting from internal memory will continue to boot into the recovery partition until they are replaced. You would be able to boot from an SD card to replace them though.

I flashed cm9 alpha 0.2 on my nook tablet using the nook tablet recovery apk. It booted into cyanoboot, however it had an error message that said disc majic error. I noticed I had put the wrong boot image on my sd card from the alpha 0.1. I rebooted 8 times and booted into cwm. Now in cwm I flashed a backup of my tablet. I then made the common mistake of clicking reboot recovery. Then trying to fix the bootloop into cwm recovery while unaware of the sevarity of what I was doing I went into mounts and storage and formated each bootdata, cache, data, emmc, rom, and system. I just restored my backup again and now I know what I need to do. My stock Nook recovery was overwriten when I clicked reboot recovery. Also I formated my rom folder and that might have contained my serial number and info.
I basicaly deleted my partions. while stuck in the cwm boot loop. Can you please send me or send me the link to a step by step way that I can get my nook tablet 16gb stuck in the cwm boot loop back to normal.
I tried using fastboot but I dont know the commands to open it. Also I dont know how to use adb either. I have a 2gig, and a 256 mb micro sd. I have a windows pc. Can you show me step by step how to restore those partions, how to do it on adb or fastboot, or the update zip method. I need help as soon as possible. Thanks.

Its similar to this

This seems like the only place folks are looking at bcb in much detail, so I thought I'd post an observation: on the simple touch, if you boot from noogie after issuing an "erase and deregister" command from the OS, the bcb file contains command strings.

I don't know what reads the strings, but after erase and deregister, bcb seems to be used to tell the device to run recovery:

recovery --wipe_data

is an ascii string from bcb on a deregistered and not yet rebooted glowworm - I put the noogie disk in, did the erase and deregister, then dumped the partitions once it came back up.

the command flags available in recovery as of cupcake are documented at

http://www.netmite.com/android/mydro...ery/recovery.c