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[Q] Many Advanced Questions Regarding ROMs

21st July 2014, 04:08 AM   |  #1  
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I am getting into development more and have a new load of questions. And yes, I searched first.


Do all Roms include firmware(OS), kernal, baseband, and boot loader?

Do over-the-air updates include the baseband and boot loader, or only the kernal and firmware/(OS).

I once used the Wugfreth toolkit to reinstall the stock ROM. It flashed the baseband with the same version and then attempted to flash the boot loader with the same version, but failed. How can I JUST flash the kernal and firmware/os.

This may be dumb question, but what language is the boot loader and baseband written in? Is it encrypted, or can anyone edit it and flash?

What happens if the boot loader, baseband, kernal, and firmware versions do not match?

I did not know the ROM included the bootloader, and I almost purposely flash the ROM of another device to see what would happen, figuring I could have restored using fastboot. But that probably would have hard-bricked it, right? I thought flashing a ROM was completely safe because it did not touch the boot loader, and could always be undone with fastboot?

How do you developers test out modified bootloaders without making a simple coding mistake and ruining your device?

How can you flash a bootloader using itself (fastboot)?

I saw a post for a different device for changing the boot loader logo. Not the firmware's boot animation. I don't want mine to say "Google" with an unlock icon. Can this be done on the Nexus 7?

I read the partition sizes are determined by the boot loader, and not adjustable. Is this correct? I am running stock 4.4.3 and only have 11MB free on the system partition. How do custom Roms fit within this limit? I am worried this will prevent a custom ROM based in 5.0 Lollipop, and the Nexus 7 2012 will be stuck on Kitkat. Maybe the firmware could be loaded on the data partition with a symbolic link to the system partition?

Thank you
21st July 2014, 06:04 PM   |  #2  
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I'm not a developer, but can answer some of your questions (at least as they relate specifically to the Nexus 7).

Custom ROMS typically just include the firmware/kernel (and i believe the radio/baseband if it's for a 3g/mobile device, though these can also be flashed separately, and i could be wrong on this part.) Bootloader is typically untouched, but this might differ on other devices.

As for OTA updates and what all they include, well that depends on the device, manufacturer, carrier, and even the specific OTA. It could potentially include everything (firmware/kernel updates, bootloader, radio/baseband, etc.), but may be any combination of the different components.

Available free space on the system partition doesn't really matter if you're flashing a new ROM, because you'll be wiping the partition as part of the flashing process. ROMs typically don't include GAPPS either (unless it's just a modified version of stock), so will actually take up much less room than the stock ROM on their own. Then you can decide which GAPPS to flash separately, there are various packages available in different sizes; some just include the basic google play services needed to have the play store and related basic functionality, others will mirror the stock pre-installed apps.

If you're using a custom recovery to flash a ROM, they typically contain a script to first verify the device matches, if not, it won't even flash. If you do manage to flash an incompatible ROM (via fastboot maybe, or if it doesn't include a verification script), with a Nexus this typically is not a big deal, you just won't ever actually boot into the ROM, but should still be able to boot into recovery or bootloader and then flash a compatible ROM.

If you flash an incompatible kernel on top of a ROM, you'll likely get a bootloop/softbricked device.

Flashing an incompatible bootloader may brick the device. Any tinkering with the bootloader is always risky.

Hope that helps a little, I'll take another look when I'm not at work
21st July 2014, 08:12 PM   |  #3  
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Quote:
Originally Posted by flyoffacliff

I am getting into development more and have a new load of questions. And yes, I searched first.


Do all Roms include firmware(OS), kernal, baseband, and boot loader?

Do over-the-air updates include the baseband and boot loader, or only the kernal and firmware/(OS).

I once used the Wugfreth toolkit to reinstall the stock ROM. It flashed the baseband with the same version and then attempted to flash the boot loader with the same version, but failed. How can I JUST flash the kernal and firmware/os.

This may be dumb question, but what language is the boot loader and baseband written in? Is it encrypted, or can anyone edit it and flash?

What happens if the boot loader, baseband, kernal, and firmware versions do not match?

I did not know the ROM included the bootloader, and I almost purposely flash the ROM of another device to see what would happen, figuring I could have restored using fastboot. But that probably would have hard-bricked it, right? I thought flashing a ROM was completely safe because it did not touch the boot loader, and could always be undone with fastboot?

How do you developers test out modified bootloaders without making a simple coding mistake and ruining your device?

How can you flash a bootloader using itself (fastboot)?

I saw a post for a different device for changing the boot loader logo. Not the firmware's boot animation. I don't want mine to say "Google" with an unlock icon. Can this be done on the Nexus 7?

I read the partition sizes are determined by the boot loader, and not adjustable. Is this correct? I am running stock 4.4.3 and only have 11MB free on the system partition. How do custom Roms fit within this limit? I am worried this will prevent a custom ROM based in 5.0 Lollipop, and the Nexus 7 2012 will be stuck on Kitkat. Maybe the firmware could be loaded on the data partition with a symbolic link to the system partition?

Thank you

1. roms dont include a bootloader.
2. no
3. easily in a custom recovery.
4. i have no idea, and its the most secure part of the device.
5. nothing.
6. roms DO NOT EVER include bootloaders.
7. developers on nexus devices never modify the bootloader. first off, its extremely tedious and difficult. secondly, there is no need, as our bootloaders are unlockable and lockable.
8. it overwrites itself, but you are on your computer using fastboot, phone is just plugged into it.
9. no.
10. each partition has its own size. roms go into a partition that also holds your storage, and is separated from the storage. another reason why you dont have 16gb storage when you buy a 16gb device, because some of it gets allocated to the system.
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