[Q] Changing Bootloader - Discussion - What's the safest way?

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Hi guys, I want to change my phone bootloader and also to a friend of mine. But I have some nasty experience with bootloader upgrading so I though that a discussion here would be good, so everyone know what to do in the future.

For example, I use ODIN for firmware upgrades, but as you all know it has a quite big rate of failures, caused by different reasons. On the other hand, we have Heimdall which is supposed to be safer and has more options than ODIN (bootloader flash only and such things).

The point is, while we are in download mode, and the flashing of bootloader fails, after restart... well... there won;t be a start anymore. The phone will be dead. What I was thinking is: what if we don't thick restart on ODIN or Heimdall and if flashing the boot loader fails, the phone will remain in download mode. Couldn't this be the opportunity to try again? After all, all we need is download mode.

We could try second time with Heimdall, or another full firmware with odin... what do you say guys?


Remaining in download mode gives us a second chance to bootloader writing?

Sorry if I've been really fuzzy in my ideas but I'm very sleepy right now.

Originally Posted by Crysis21

Remaining in download mode gives us a second chance to bootloader writing?

Unfortunately no. If a flash fails it's because the phone has stopped responding to commands. The phone won't continue responding to commands until you've booted into download mode again. It's for this very reason I don't actually have a "no reboot" option for Heimdall, it would be pretty much pointless.

However luckily if you're just flashing a secondary bootloader the device can still be booted up using a custom jig. This is because devices store a backup secondary bootloader that can be used if the first one is corrupt. A custom jig seems to cause the device to boot using this backup secondary bootloader.

However as far as I can tell if you stuff up the primary bootloader then you're toast. This would require a JTAG fix. I'm not actually sure if this has ever even happened though.

The thing is, 4 months ago I ended up on JTAG. After messing the bootloader I managed to get download mode with custom JIG. But after that I don;t know exactly the mistakes I've made, but I ended up with a dead phone. No JIG working, nothing. So... yes it happened. I am toasted already with bootloader changing) that's why I was asking if remaining in Download mode helps with somthing.

Thanks for your answer

Sorry I should have been clear. I know there are cases where users have hard-bricked their phone and not even a custom jig would help so JTAG was required.

During the early stages of Heimdall's development, prior to the custom jig discovery, I bricked my device to the point of not being able to charge. This was because either boot.bin or params.lfs failed to flash due to a bug in a alpha release of Heimdall. We didn't know about custom jigs then so I was unable to actually test if it was recoverable.

However, all the hard-brick cases that I've heard sufficient detail about, turn out to be a result of users flashing a primary bootloader that was not designed for their device. So what I should have said is that I'm not sure if anyone has ever actually failed to sucessfully flash a primary bootloader (other than me with an alpha build).

Anyway unfortunately there's not a whole lot that can be done to 100% remove the risk of bricking. Either the secondary bootloader USB control software is buggy or the hardware itself is crap and sometimes it doesn't get on well with some people's USB ports. Unless we come up with a way to easily replace the bootloaders from the device itself then the best thing you can do is use a reliable USB port.

Thanks for the information...