add translated content from russian wiki

en/help-uboot.md

@@ -20,3 +20,111 @@ __OpenIPC Linux:__
 root@openipc-hi3518ev100:~# fw_setenv uk 'mw.b 0x82000000 ff 1000000; tftp 0x82000000 uImage.${soc}; sf probe 0; sf erase 0x50000 0x200000; sf write 0x82000000 0x50000 ${filesize}'
 root@openipc-hi3518ev100:~#
 ```
+
+### Saving original firmware without using tftp.
+
+In the terminal program you use connect to UART port with, enable saving a log
+file of the session. I like to use `screen` for that, and my command to connect
+to the UART adapter with logging of the active session into a file would look
+like this:
+```
+$ screen -L -Logfile fulldump.log /dev/ttyUSB0 115200
+```
+
+After connecting to bootloader console, run a command for reading hexadecimal
+dump of data from the very beginning of the flash memery to the very end of it.
+Use hexadecimal notation for addresses, where 0 is 0x0, 8 MB is 8x00000, and
+16 MB is 0x1000000. 
+
+For reading whole 8 MB flash memory run 
+```
+md.b 0x0 0x800000
+```
+and for 16 MB flash memory run
+```
+md.b 0x0 0x1000000
+```
+Since the process of reading is going to take a considerable amount of time
+(literally hours), you might want to disconnect from the terminal session to
+avoid accidental keystrokes contaminating the output. Press `Ctrl-a` followed
+by `d` to detach the session from active terminal. Run `screen -r` when you 
+need to reconnect it later, after the size of the log file will stop growing.
+Reading of an 8 MB flash memory should result in a ~40 MB log file, and for a
+16 MB chip the file should be twice that size.
+
+Convert the hex dump into a binary firmware file using `xxd` and keep it for
+further research or restoring camera to its pristine state.
+
+Using [binwalk](https://github.com/ReFirmLabs/binwalk) to unpack the binary file. 
+
+#### Saving firmware via SD card.
+
+Sometimes your camera only has a wireless connection, which does not work
+directly from the bootloader. Very often such cameras have a microSD card slot.
+In this case you can try to save a copy of the original firmware using an
+SD card as an intermediary medium.
+
+Since you're going to save firmware in its binary form, the amount of data will
+be either 8 MB or 16 MB, depending on the size of camera's flash memory chip.
+So any SD card will do, even the smallest one.
+
+Insert the card into the card slot on the camera, connect the serial adapter to
+the UART port, supply power to the camera and stop the boot process to get into
+the bootloader console.
+
+Initialize access to the card, and clear some space to save firmware on.
+Data is written onto card in blocks of 512 bytes. You need to erase 16384 blocks
+to clear 8 MB, 32768 blocks for 16 MB, which are 0x4000 and 0x8000 hexadecimal,
+respectively.
+
+Note that we are going to write directly to the card registers, bypassing the
+partition table. To avoid conflicts when accessing card data later from your PC,
+offset 8 kilobytes from the beginning of the card (8 * 1024 = 8192 bytes or 16
+blocks of 512 bytes, or 0x10 blocks in hexadecimal representation).
+
+```
+mmc dev 0
+mmc erase 0x10 0x8000
+```
+
+Now you need to copy the contents of the firmware from the flash memory chip to
+the RAM of the camera. To do that, clear a section of RAM (0x800000 bytes for a
+8MB chip or 0x1000000 bytes for a 16MB chip), read the flash memory and copy
+the entire contents to the prepared space in RAM. Then export the copied data
+from RAM to the card.
+
+NB! In the example below we use the starting address 0x2000000, but it varies
+for different cameras. Please consult SoC data sheet, or seek help on
+[our Telegram channel][telegram].
+
+```
+mw.b 0x2000000 ff 0x1000000
+sf probe 0
+sf read 0x2000000 0x0 0x1000000
+mmc write 0x2000000 0x10 0x8000
+```
+
+Remove the card from the camera and insert it into a computer running Linux.
+Use `dd` command to copy data from the card to a binary file on the computer.
+
+```
+dd bs=512 skip=16 count=32768 if=/dev/sdc of=./fulldump.bin
+```
+
+### Bypassing password-protected bootloader.
+
+Changing the bootloader is a risky operation. There's a high probability of
+turning your camera into a paperweight if something goes wrong. So before you
+flash a new bootloader you have to weigh up all the risks and benefits. In most
+cases the original bootloader plus new kernel and new operating system should
+work just fine. But there are exceptions.
+
+Today, we see more and more cameras where access to bootloader console is
+protected with a password. Thus, even if you connect to the camera's UART port,
+all you will see after interrupting the standard boot cycle is a prompt for
+password. In that case, a relatively safe solution is to downgrade the firmware
+to a version where the password protection was not yet implemented. For example,
+for Xiongmai cameras the bootloader password protection started popping up
+somewhere around July 2021, hence you need a firmware for your camera from an
+earlier date. After you successfully downgrade your camera to a password-free
+bootloader, you could install the OpenIPC firmware in a regular way.