Solved Implementation of the fastboot protocol

[AbelChT]

Hi,
I have two questions related to the fastboot protocol.

How is it integrated into the boot process of the phone?
For example in a PC with bios and with Linux, the boot process starts with the BIOS, then takes place the bootloader, then the Linux kernel, etc.

I expect that in an Android smartphone, the fastboot take place before the bootloader, but I would like to clarify it.

The second question is related to how is it stored in the device. Is it flashed in a ROM (read-only memory) in the phone, or is stored in the internal memory?

If it is device dependant, the device I am using for development is an Xperia T3.

Any help is appreciated.

[devjerpelea]

Hello,

Thanks for the question

Here is a good explanation what fastboot is
https://www.androidcentral.com/android-z-what-fastboot

and a good diagram for the boot process
https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/The-Android-Booting-process/ta-p/1129182

Best regards
Alin

[AbelChT]

@Jerpelea-Alin

Hi,
Thanks for your quick response.

The links that you shared with me helped me, but I still have some doubts.

I have read these two posts where the boot process is explained more in detail:

• https://forum.xda-developers.com/t/info-boot-process-android-vs-linux.3785254/
• http://newandroidbook.com/Articles/aboot.html

In the first one, it says that if we want to enter fastboot mode, it is the android bootloader (aboot) the one in charge of doing this operation.

If I am not wrong, this means that if I corrupt the boot partition when installing a new kernel, I will be able to recover my phone via fastboot or using the Flash tool (https://developer.sony.com/develop/open-devices/get-started/flash-tool/). Is it correct?

I take this opportunity to ask another question.
From what I have read, if I unlock the bootloader some proprietary blobs are erased. If I use the flash tool to recover a stock image after unlocking the bootloader, will I recover these blobs?

Best regards

[devjerpelea]

Hi AbelChT,

The fastboot/flash mode are stored on a partition that is not available to users and should be fairly safe to assume that if you follow the guides provided on our website there will not be any issue.

The kernel (boot.img & recovery.img) is stored on separate partitions and even if you flash a broken kernel/OS you can always go to the fastboot (blue light) / flash (green light) mode to recover your device. You can always use the flashtool to flash the Sony image and recover from a bad OS update if your custom ROM does not boot.

Please note that during the unlock process the userdata is wiped.

Best regards
Alin

[dmelnik3289]

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