Documentation: Add guide for fastboot

See apache/nuttx-apps#2562

Signed-off-by: wangjianyu3 <[email protected]>

Author: JianyuWang0623

Documentation/applications/system/fastboot/index.rst

@@ -1,3 +1,34 @@
 ======================
 ``fastboot`` fastbootd
 ======================
+Prepare
+==========================
+
+- Check fastboot tool(Host): :code:`fastboot --version`
+- Download fastboot tool and install(Host): `platform-tools <https://developer.android.com/tools/releases/platform-tools>`__
+- Enable the fastbootd application(Device): :code:`CONFIG_USBFASTBOOT=y` and :code:`CONFIG_SYSTEM_FASTBOOTD=y`
+- Start fastbootd(Device): :code:`fastbootd &`
+
+Commands
+==========================
+- :code:`fastboot reboot [FLAG]`: Reboot the device, more details for :code:`[FLAG]`: `g_resetflag <https://github.com/apache/nuttx-apps/blob/master/nshlib/nsh_syscmds.c#L114>`__ and `boardioc_softreset_subreason_e <https://github.com/apache/nuttx/blob/master/include/sys/boardctl.h#L458>`__
+- :code:`fastboot flash <PARTITION> <FILENAME>`: Flash partition :code:`<PARTITION>` using the given :code:`<FILENAME>`
+- :code:`fastboot erase <PARTITION>`: Erase given partition
+- Get Variables
+   - :code:`fastboot getvar product`: Get product name
+   - :code:`fastboot getvar kernel`: Get kernel name
+   - :code:`fastboot getvar version`: Get OS version string
+   - :code:`fastboot getvar slot-count`: Get slot count
+   - :code:`fastboot getvar max-download-size`: Get max download size
+- OEM
+   - :code:`fastboot oem filedump <PARTITION> [OFFSET] [LENGTH]`: Get :code:`<LENGTH>` (full by default) bytes of :code:`<PARTITION>` from :code:`<OFFSET>` (zero by default)
+   - :code:`fastboot oem memdump <ADDRESS> <LENGTH>`: Dump :code:`<LENGTH>` bytes memory from address :code:`<ADDRESS>`
+- :code:`fastboot get_staged <OUT_FILE>`: Writes data staged by the last command to file :code:`<OUT_FILE>`. e.g. "oem filedump" and "oem memdump"
+
+Examples
+==========================
+- Exit fastboot mode: :code:`fastboot reboot`
+- Flash app.bin to partition /dev/app: :code:`fastboot flash app ./app.bin`
+- Erase partition /dev/userdata: :code:`fastboot erase userdata`
+- Dump partition /dev/app: :code:`fastboot filedump /dev/app` and then :code:`fastboot get_staged ./dump_app.bin`
+- Dump memory from 0x44000000 to 0x440b6c00: :code:`fastboot oem memdump 0x44000000 0xb6c00` and then :code:`fastboot get_staged ./mem_44000000_440b6c00.bin`