1*4882a593SmuzhiyunMediatek MT8173 aka Chromebook Elm 2*4882a593Smuzhiyun================================== 3*4882a593Smuzhiyun 4*4882a593SmuzhiyunThis file describes booting the Chromebook from an SD card containing 5*4882a593SmuzhiyunBuildroot kernel and rootfs, using the original bootloader. This is 6*4882a593Smuzhiyunthe least invasive way to get Buildroot onto the devices and a good 7*4882a593Smuzhiyunstarting point. 8*4882a593Smuzhiyun 9*4882a593SmuzhiyunThe bootloader will only boot a kernel from a GPT partition marked 10*4882a593Smuzhiyunbootable with cgpt tool from vboot-utils package. 11*4882a593SmuzhiyunThe kernel image must be signed using futility from the same package. 12*4882a593SmuzhiyunThe signing part is done by sign.sh script in this directory. 13*4882a593Smuzhiyun 14*4882a593SmuzhiyunIt does not really matter where rootfs is as long as the kernel is able 15*4882a593Smuzhiyunto find it, but this particular configuration assumes the kernel is on 16*4882a593Smuzhiyunpartition 1 and rootfs is on partition 2 of the SD card. 17*4882a593SmuzhiyunMake sure to check kernel.args if you change this. 18*4882a593Smuzhiyun 19*4882a593SmuzhiyunMaking the boot media 20*4882a593Smuzhiyun--------------------- 21*4882a593SmuzhiyunStart by configuring and building the images. 22*4882a593Smuzhiyun 23*4882a593Smuzhiyun make chromebook_elm_defconfig 24*4882a593Smuzhiyun make menuconfig # if necessary 25*4882a593Smuzhiyun make 26*4882a593Smuzhiyun 27*4882a593SmuzhiyunThe important files are: 28*4882a593Smuzhiyun 29*4882a593Smuzhiyun uImage.kpart (kernel and device tree, signed) 30*4882a593Smuzhiyun rootfs.tar 31*4882a593Smuzhiyun bootsd.img (SD card image containing both kernel and rootfs) 32*4882a593Smuzhiyun 33*4882a593SmuzhiyunWrite the image directly to some SD card. 34*4882a593SmuzhiyunWARNING: make sure there is nothing important on that card, 35*4882a593Smuzhiyunand double-check the device name! 36*4882a593Smuzhiyun 37*4882a593Smuzhiyun SD=/dev/mmcblk1 # may be /dev/sdX on some hosts 38*4882a593Smuzhiyun dd if=output/images/bootsd.img of=$SD 39*4882a593Smuzhiyun 40*4882a593SmuzhiyunSwitching to developer mode and booting from SD 41*4882a593Smuzhiyun----------------------------------------------- 42*4882a593SmuzhiyunPower Chromebook down, then power it up while holding Esc+F3. 43*4882a593SmuzhiyunBEWARE: switching to developer mode deletes all user data. 44*4882a593SmuzhiyunCreate backups if you need them. 45*4882a593Smuzhiyun 46*4882a593SmuzhiyunWhile in developer mode, Chromebook will boot into a white screen saying 47*4882a593Smuzhiyun"OS verification is off". 48*4882a593Smuzhiyun 49*4882a593SmuzhiyunPress Ctrl-D at this screen to boot Chromium OS from eMMC. 50*4882a593SmuzhiyunPress Ctrl-U at this screen to boot from SD (or USB) 51*4882a593SmuzhiyunPress Power to power it off. 52*4882a593SmuzhiyunDo NOT press Space unless you mean it. 53*4882a593SmuzhiyunThis will switch it back to normal mode. 54*4882a593Smuzhiyun 55*4882a593SmuzhiyunThe is no way to get rid of the white screen without re-flashing the bootloader. 56*4882a593Smuzhiyun 57