Dual-Q H721 is a router platform board, it is the smaller model of
the U7621-06.

The device has the following specifications:

MT7621AT (880 MHz)
256 of RAM (DDR3)
16 MB of FLASH (MX25l12805d SPI)
5x 1 Gbps Ethernet (MT7621 built-in switch)
1x M.2 (NGFF) 3.7V 3A max for 5G M.2 Modem work at USB3.0 mode
1x Minipcie 3.7V 3A max for LTE Modem work at USB2.0 Mode
2x Minipcie for WIFI card
4x Lan+1x Wan 10/100M/1000M RJ45 port
14x LEDs (1x GPIO-controlled)
1x reset button
1x UART header (4-pins)
1x mico SD-card reader
1x DC jack for main power (5~27 V)

The following has been tested and is working:

Ethernet switch
miniPCIe slots (tested with Wi-Fi cards and LTE modem cards)
miniSIM slot (works with normal size simcard)
sysupgrade
reset button
micro SD-card reader

Installation:

This board has no locked down bootloader. The seller can be asked to
install openwrt, so upgrades are standard sysupgrade method.

Recovery:

This board contains a Chinese, closed-source bootloader called Breed
(Boot and Recovery Environment for Embedded Devices). Breed supports web
recovery and to enter it, you keep the reset button pressed for around
5 seconds during boot. Your machine will be assigned an IP through DHCP
and the router will use IP address 192.168.1.1. The recovery website is
in Chinese, but is easy to use. Click on the second item in the list to
access the recovery page, then the second item on the next page is where
you select the firmware. In order to start the recovery, you click the
button at the bottom.

Signed-off-by: Dawsen Gao <dawsen_gao@163.com>
[change author name (used SoB one), add ethernet pinctrl,
 apply sorting to device recipe]
Signed-off-by: Sungbo Eo <mans0n@gorani.run>