NV U-Boot on Samsung XE303C12

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NV U-Boot on Samsung XE303C12

Postby TheForgottenKing » Sat Jun 24, 2017 2:50 am

Special thanks to doragasu1 for finding this...

Please note that you can install Arch Linux ARM and remove Chrome OS without using this tutorial, simply boot off of the created USB drive/SD card and repeat the install process using /dev/mmcblk0, the main EMMC. This should not be necessary unless you want to be able to boot into Chrome OS/Arch at boot time or to install mainline kernel without using a third partition

Image with the HWID set as DAISY TEST A-A 9382 (No automatic updates)
https://mega.nz/#!RKxTASqK!mdFXa4vAaK4s ... V8sFnrqM3M

Image with the HWID set as SNOW BARA A-J 9464 (Automatic updates should work)
https://mega.nz/#!NWxEVJIK!gBJdjbegscOZ ... HByYJq3jpw

To flash to the SPI Flash:
Code: Select all
flashrom -p linux_spi:dev=/dev/spidev1.0 -r original_image-snow.bin
flashrom -p linux_spi:dev=/dev/spidev1.0 -w nv_image-snow.bin


If you are using the modified HWID run
Code: Select all
flashrom -p linux_spi:dev=/dev/spidev1.0 -r original_image-snow.bin
flashrom -p linux_spi:dev=/dev/spidev1.0 -w nv_image-snow-hwid.bin


If you are in arch, make sure to install flashrom.google, the default package will not work:
Code: Select all
pacman -Syu flashrom.google

as root

As per usual, no one except for you is responsible for the safety of your own device, and this is at your own risk

Recovery in case of hardbrick:
Written by resucant but quoting is broken for me
Thanks for posting these instructions! They worked well.

I managed to temporarily brick my Chromebook shortly afterwards however by flashing a self compiled u-boot image, so I thought I'd post my recovery procedure for anyone in the same situation. Basically it's this method for the Galaxy S2 applied to the Chromebook. You solder some connections on the mainboard to configure the processor to boot directly from the SD card rather than the SPI flash.

The boot mode configuration resistors for the Chromebook are located here:

Image

After trying many different combinations of solder bridges I found one that booted the SD card:

Image

Make sure to check with a multimeter that you haven't shorted 1.8V and ground before reconnecting the battery.

Write the u-boot image to the second sector of an SD card. For example in Linux:
Code: Select all
dd if=nv_image-snow.bin of=/dev/mmcblk1 bs=512 seek=1

This is so that you can still have a partition table in the first sector (but make sure that the first partition starts after the 4MB u-boot image).

Then plug the card into the modified chromebook, press the power button, mash keys, and you should see the u-boot prompt. From there you can type 'boot' to boot chrome, or use other u-boot commands to boot arch linux (see strata's post quoted above for examples).

Strata's Post:
Code: Select all
setenv bootargs root=/dev/mmcblk1p2 rootfstype=jfs rootwait rw
mmc dev 1
ext2load mmc 1:1 42000000 vmlinux.uimg
bootm 42000000


Note that if you choose to flash a working u-boot image to your SPI flash, you will need to remove the solder bridges to boot from it. With the solder bridges in place, the Chromebook will not attempt to boot SPI flash at all, even if the SD card is removed.


Using this you can have boot arguments, you can use verified boot by running vboot_twostop, or you can use boot commands (search the internet, I'm still using vboot_twostop for now)

I'll update this with how to boot uImage kernels from emmc. I've modified the partition layout and installed a verified arch kernel to /dev/mmcblk0p6 root to /dev/mmcblk0p7 and a 64mb boot partition at /dev/mmcblk0p13 which is added by shrinking the rootfs and adding a partition using cgpt.

vboot_twostop to load verified firmware

Make sure to check all commands before running, comment in case I messed up names.
TheForgottenKing
 
Posts: 8
Joined: Thu May 18, 2017 2:28 am

Re: NV U-Boot on Samsung XE303C12

Postby TheForgottenKing » Thu Jul 20, 2017 3:53 am

Wierd, sound isn't working when flashed.
TheForgottenKing
 
Posts: 8
Joined: Thu May 18, 2017 2:28 am


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