57 lines
1.9 KiB
Plaintext
57 lines
1.9 KiB
Plaintext
Mediatek MT8173 aka Chromebook Elm
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==================================
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This file describes booting the Chromebook from an SD card containing
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Buildroot kernel and rootfs, using the original bootloader. This is
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the least invasive way to get Buildroot onto the devices and a good
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starting point.
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The bootloader will only boot a kernel from a GPT partition marked
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bootable with cgpt tool from vboot-utils package.
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The kernel image must be signed using futility from the same package.
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The signing part is done by sign.sh script in this directory.
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It does not really matter where rootfs is as long as the kernel is able
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to find it, but this particular configuration assumes the kernel is on
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partition 1 and rootfs is on partition 2 of the SD card.
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Make sure to check kernel.args if you change this.
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Making the boot media
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---------------------
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Start by configuring and building the images.
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make chromebook_elm_defconfig
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make menuconfig # if necessary
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make
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The important files are:
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uImage.kpart (kernel and device tree, signed)
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rootfs.tar
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bootsd.img (SD card image containing both kernel and rootfs)
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Write the image directly to some SD card.
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WARNING: make sure there is nothing important on that card,
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and double-check the device name!
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SD=/dev/mmcblk1 # may be /dev/sdX on some hosts
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dd if=output/images/bootsd.img of=$SD
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Switching to developer mode and booting from SD
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-----------------------------------------------
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Power Chromebook down, then power it up while holding Esc+F3.
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BEWARE: switching to developer mode deletes all user data.
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Create backups if you need them.
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While in developer mode, Chromebook will boot into a white screen saying
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"OS verification is off".
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Press Ctrl-D at this screen to boot Chromium OS from eMMC.
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Press Ctrl-U at this screen to boot from SD (or USB)
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Press Power to power it off.
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Do NOT press Space unless you mean it.
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This will switch it back to normal mode.
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The is no way to get rid of the white screen without re-flashing the bootloader.
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