diff options
Diffstat (limited to 'doc/android/bcb.txt')
| -rw-r--r-- | doc/android/bcb.txt | 89 |
1 files changed, 0 insertions, 89 deletions
diff --git a/doc/android/bcb.txt b/doc/android/bcb.txt deleted file mode 100644 index 7b7177cacf..0000000000 --- a/doc/android/bcb.txt +++ /dev/null @@ -1,89 +0,0 @@ -Android Bootloader Control Block (BCB) - -The purpose behind this file is to: - - give an overview of BCB w/o duplicating public documentation - - describe the main BCB use-cases which concern U-Boot - - reflect current support status in U-Boot - - mention any relevant U-Boot build-time tunables - - precisely exemplify one or more use-cases - -Additions and fixes are welcome! - - -1. OVERVIEW ---------------------------------- -Bootloader Control Block (BCB) is a well established term/acronym in -the Android namespace which refers to a location in a dedicated raw -(i.e. FS-unaware) flash (e.g. eMMC) partition, usually called "misc", -which is used as media for exchanging messages between Android userspace -(particularly recovery [1]) and an Android-capable bootloader. - -On higher level, BCB provides a way to implement a subset of Android -Bootloader Requirements [2], amongst which are: - - Android-specific bootloader flow [3] - - Get the "reboot reason" (and act accordingly) [4] - - Get/pass a list of commands from/to recovery [1] - - TODO - - -2. 'BCB'. SHELL COMMAND OVERVIEW ------------------------------------ -The 'bcb' command provides a CLI to facilitate the development of the -requirements enumerated above. Below is the command's help message: - -=> bcb -bcb - Load/set/clear/test/dump/store Android BCB fields - -Usage: -bcb load <dev> <part> - load BCB from mmc <dev>:<part> -bcb set <field> <val> - set BCB <field> to <val> -bcb clear [<field>] - clear BCB <field> or all fields -bcb test <field> <op> <val> - test BCB <field> against <val> -bcb dump <field> - dump BCB <field> -bcb store - store BCB back to mmc - -Legend: -<dev> - MMC device index containing the BCB partition -<part> - MMC partition index or name containing the BCB -<field> - one of {command,status,recovery,stage,reserved} -<op> - the binary operator used in 'bcb test': - '=' returns true if <val> matches the string stored in <field> - '~' returns true if <val> matches a subset of <field>'s string -<val> - string/text provided as input to bcb {set,test} - NOTE: any ':' character in <val> will be replaced by line feed - during 'bcb set' and used as separator by upper layers - - -3. 'BCB'. EXAMPLE OF GETTING REBOOT REASON ------------------------------------ -if bcb load 1 misc; then - # valid BCB found - if bcb test command = bootonce-bootloader; then - bcb clear command; bcb store; - # do the equivalent of AOSP ${fastbootcmd} - # i.e. call fastboot - else if bcb test command = boot-recovery; then - bcb clear command; bcb store; - # do the equivalent of AOSP ${recoverycmd} - # i.e. do anything required for booting into recovery - else - # boot Android OS normally - fi -else - # corrupted/non-existent BCB - # report error or boot non-Android OS (platform-specific) -fi - - -4. ENABLE ON YOUR BOARD ------------------------------------ -The following Kconfig options must be enabled: -CONFIG_PARTITIONS=y -CONFIG_MMC=y -CONFIG_BCB=y - -[1] https://android.googlesource.com/platform/bootable/recovery -[2] https://source.android.com/devices/bootloader -[3] https://patchwork.ozlabs.org/patch/746835/ - ("[U-Boot,5/6] Initial support for the Android Bootloader flow") -[4] https://source.android.com/devices/bootloader/boot-reason |