Ralink/MediaTek U-Boot for MIPS SoC
    RT3052/RT3352/RT3883/RT5350/MT7620/MT7621/MT7628/MT7688
                 Based on MediaTek SDK 5.0.1.0

Preparing Toolchain

For MT7621 U-Boot:

• extract 'toolchain/mips-2012.03.tar.bz2' to /opt (tar -xvf toolchain/mips-2012.03.tar.xz -C /opt/)

For RT3XXX/MT7620/MT7628/MT7688 U-Boot:

• extract 'toolchain/buildroot-gcc342.tar.bz2' to /opt

Both toolchains require x86 (32-bit) Linux environment. If you are on x64 (64-bit) environment you need to do the following: Ubuntu 18.04 or Debian 9,10

dpkg --add-architecture i386

apt install libc6:i386 libncurses5:i386 libstdc++6:i386

Build Instructions

• Copy appropriate '.config' file (e.g. profiles/XIAOMI/MI-R4AG_SPI/.config) to 'uboot-5.x.x.x' dir.
• Goto 'uboot-5.x.x.x' dir.
• Run 'make menuconfig', choose [Exit] and confirm [Save]. This is important step!
• Run 'make'.
• Use image file uboot.bin (ROM mode) for NOR and SPI-flash boards.
• Use image file uboot.img (RAM mode) for NAND-flash boards.

To clean U-Boot tree:

• Run 'make clean'.
• Run 'make unconfig'.

Build for new Boards

• Goto 'uboot-5.x.x.x' dir.
• Run 'make menuconfig'.
• Select SoC, Ram, Flash type for your board. See some .config from profiles, you will get the general idea.
• Choose [Exit] and confirm [Save] then run 'make'.

NOTE:

1. Before building for a new board, know the GPIO number for reset, leds and configure them properly during 'make menuconfig'. Extra careful with the reset button (GPIO_BTN_RESET).
2. It's better to configure UART baud rate same as your stock firmware 115200 or 57600.
3. All profiles has disabled option "Enable all Ethernet PHY" to prevent LAN-WAN spoofing (EPHY will be enabled later in FW logic). To force enable EPHY (e.g. for use OpenWRT/PandoraBox), select option "Enable all Ethernet PHY".
4. See if your board's spi or nand flash chip is listed on here 'uboot-5.x.x.x/drivers/spi_flash.c' (281 line) or 'uboot-5.x.x.x/drivers/nand/nand_device_list.h'. Don't risk it if your flash chip is not on the list.

Flash Instructions

Take a backup of the current u-boot partition (mtd0):

root@OpenWrt:/tmp# dd if=/dev/mtd0 of=uboot_orig.bin
256+0 records in
256+0 records out

Transfer the backup off the device and to a safe place:

me@laptop:~# scp [email protected]:/tmp/uboot_orig.bin .
uboot_orig.bin                                100%  128KB 128.0KB/s   00:00

Beware: This step may differ for other devices. I'm using TP-Link TL-MR3220v2 and it uses the first 64 KiB block to store compressed U-Boot image. In the second 64 KiB block they store additional information like MAC address, model number and WPS pin number. This means the old backup is bigger than the new one we're going to flash. To store the old settings we're going to modify only the compressed U-Boot image and leave the additional information intact. To do that, take a copy of the original file, and copy the new image over it without truncating the leftover bytes:

root@OpenWrt:/tmp# cp uboot_orig.bin uboot_new.bin
root@OpenWrt:/tmp# dd if=uboot_for_tp-link_tl-mr3220_v2.bin of=uboot_new.bin conv=notrunc
128+0 records in
128+0 records out

Danger: This is the point of no return, if you have any errors or problems, please revert the original image at any time using:

root@OpenWrt:/tmp# mtd write uboot_orig.bin "u-boot"
Unlocking u-boot ...

Writing from uboot_orig.bin to u-boot ...

Now, to actually flash the new image, run:

root@OpenWrt:/tmp# mtd write uboot_new.bin "u-boot"
Unlocking u-boot ...

Writing from uboot_new.bin to u-boot ...

To verify that the image was flashed correctly, you should verify it:

root@OpenWrt:/tmp# mtd verify uboot_new.bin "u-boot"
Verifying u-boot against uboot_new.bin ...
a80c3a8683345a3fb311555c5d4194c5 - u-boot
a80c3a8683345a3fb311555c5d4194c5 - uboot_new.bin
Success

• Upload appropriate U-Boot image file to router's /tmp dir (e.g. via WinSCP or just wget it by creating a local http server).
• Check U-Boot image checksum and compare with uboot.md5:

md5sum /tmp/uboot.bin

Double check the boot partition name 'Bootloader' by 'cat /proc/mtd', usually it's on /dev/mtd0 or sometimes mtd1.

• Reboot router.

                         WARNING
  

• Do not remove power supply during flash U-Boot!!!

• Device may be bricked due to your incorrect actions!!!

Main Features

1. Press and hold the RESET button on Power-On for 2~3 sec, this will switch to Recovery mode. Set your Ethernet ipv4 to 192.168.1.2, subnet mask 255.255.255.0 and gateway 192.168.1.1.
2. Go to 192.168.1.1 from any browser and upload or upgrade your firmware. You can also upgrade your factory and u-boot partition from 192.168.1.1/factory.html and 192.168.1.1/uboot.html respectively.

3. Also you can use TFTP client or ASUS Firmware Restoration (device IP-address is 192.168.1.1). Some devices with usb port can also support Recovery from USB storage.

NOTE:

• U-Boot will perform switch to Recovery mode on flash content integrity fail.
• Alert LED(s) is blinking in Recovery mode and on erasing/flashing.
• To Recovery from USB storage, place FW image with a filename 'root_uImage' to first FAT16/FAT32 partition, plug-in USB2 pen and switch to Recovery mode (see 3).