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Android Fastboot
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Overview
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========
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The protocol that is used over USB is described in
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README.android-fastboot-protocol in same directory.
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The current implementation is a minimal support of the erase command,the
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"oem format" command and flash command;it only supports eMMC devices.
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Client installation
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===================
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The counterpart to this gadget is the fastboot client which can
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be found in Android's platform/system/core repository in the fastboot
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folder. It runs on Windows, Linux and even OSX. Linux user are lucky since
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they only need libusb.
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Windows users need to bring some time until they have Android SDK (currently
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http://dl.google.com/android/installer_r12-windows.exe) installed. You
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need to install ADB package which contains the required glue libraries for
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accessing USB. Also you need "Google USB driver package" and "SDK platform
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tools". Once installed the usb driver is placed in your SDK folder under
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extras\google\usb_driver. The android_winusb.inf needs a line like
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%SingleBootLoaderInterface% = USB_Install, USB\VID_0451&PID_D022
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either in the [Google.NTx86] section for 32bit Windows or [Google.NTamd64]
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for 64bit Windows. VID and PID should match whatever the fastboot is
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advertising.
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Board specific
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==============
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The fastboot gadget relies on the USB download gadget, so the following
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options must be configured:
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CONFIG_USB_GADGET_DOWNLOAD
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CONFIG_G_DNL_VENDOR_NUM
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CONFIG_G_DNL_PRODUCT_NUM
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CONFIG_G_DNL_MANUFACTURER
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NOTE: The CONFIG_G_DNL_VENDOR_NUM must be one of the numbers supported by
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the fastboot client. The list of vendor IDs supported can be found in the
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fastboot client source code (fastboot.c) mentioned above.
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The fastboot function is enabled by defining CONFIG_USB_FUNCTION_FASTBOOT,
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CONFIG_CMD_FASTBOOT and CONFIG_ANDROID_BOOT_IMAGE.
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The fastboot protocol requires a large memory buffer for downloads. This
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buffer should be as large as possible for a platform. The location of the
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buffer and size are set with CONFIG_FASTBOOT_BUF_ADDR and
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CONFIG_FASTBOOT_BUF_SIZE.
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Fastboot partition aliases can also be defined for devices where GPT
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limitations prevent user-friendly partition names such as "boot", "system"
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and "cache". Or, where the actual partition name doesn't match a standard
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partition name used commonly with fastboot. Current implentation checks
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aliases when accessing partitions by name (flash_write and erase functions).
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To define a partition alias add an environment variable similar to:
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fastboot_partition_alias_<alias partition name>=<actual partition name>
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Example: fastboot_partition_alias_boot=LNX
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Partition Names
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===============
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The Fastboot implementation in U-boot allows to write images into disk
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partitions (currently on eMMC). Target partitions are referred on the host
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computer by their names.
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For GPT/EFI the respective partition name is used.
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For MBR the partitions are referred by generic names according to the
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following schema:
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<device type> <device index letter> <partition index>
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Example: hda3, sdb1, usbda1
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The device type is as follows:
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* IDE, ATAPI and SATA disks: hd
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* SCSI disks: sd
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* USB media: usbd
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* MMC and SD cards: mmcsd
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* Disk on chip: docd
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* other: xx
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The device index starts from 'a' and refers to the interface (e.g. USB
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controller, SD/MMC controller) or disk index. The partition index starts
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from 1 and describes the partition number on the particular device.
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Writing Partition Table
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=======================
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Fastboot also allows to write the partition table to the media. This can be
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done by writing the respective partition table image to a special target
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"gpt" or "mbr". These names can be customized by defining the following
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configuration options:
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CONFIG_FASTBOOT_GPT_NAME
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CONFIG_FASTBOOT_MBR_NAME
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In Action
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=========
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Enter into fastboot by executing the fastboot command in u-boot and you
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should see:
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|GADGET DRIVER: usb_dnl_fastboot
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On the client side you can fetch the bootloader version for instance:
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|>fastboot getvar bootloader-version
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|bootloader-version: U-Boot 2014.04-00005-gd24cabc
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|finished. total time: 0.000s
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or initiate a reboot:
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|>fastboot reboot
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and once the client comes back, the board should reset.
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You can also specify a kernel image to boot. You have to either specify
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the an image in Android format _or_ pass a binary kernel and let the
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fastboot client wrap the Android suite around it. On OMAP for instance you
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take zImage kernel and pass it to the fastboot client:
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|>fastboot -b 0x80000000 -c "console=ttyO2 earlyprintk root=/dev/ram0
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| mem=128M" boot zImage
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|creating boot image...
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|creating boot image - 1847296 bytes
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|downloading 'boot.img'...
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|OKAY [ 2.766s]
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|booting...
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|OKAY [ -0.000s]
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|finished. total time: 2.766s
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and on the gadget side you should see:
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|Starting download of 1847296 bytes
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|........................................................
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|downloading of 1847296 bytes finished
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|Booting kernel..
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|## Booting Android Image at 0x81000000 ...
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|Kernel load addr 0x80008000 size 1801 KiB
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|Kernel command line: console=ttyO2 earlyprintk root=/dev/ram0 mem=128M
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| Loading Kernel Image ... OK
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|OK
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|Starting kernel ...
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