TP-Link Archer C2 AC750

→ Install OpenWrt (generic explanation)

As per the instructions in the git commit adding support for the Archer C2 AC750 v1, you need an OpenWrt image with integrated bootloader when flashing through TFTP (TP-Link pretty much always has the bootloader integrated in their firmwares). OpenWrt 19.07.1 can be flashed via TFTP using an unofficial recovery image provided here; however, if you are familiar with the command line and have access to a Linux box, it's recommended you build such an image yourself, as you'll be able to use the latest OpenWrt stable release. See instructions below.

If you feel uncomfortable doing this, grab the prepped 19.07.1 image linked to above and skip this section.

The C2v1 TFTP recovery overwrites the uboot partition, hence it must be included in a recovery.bin An official stock TPLink firmware file has a 512 byte header, which needs to be stripped for TFTP. You need access to a Linux box for this procedure (Windows Subsystem for Linux ('WSL') might work as well). Instructions below are taken from the git commit that added support into OpenWrt.

1. Download a stock TP-Link Firmware file from the TP-Link homepage.

2. Extract u-boot from the binary file:

$ dd if=c2v1_stock_firmware.bin of=c2v1_uboot.bin bs=1 skip=512 count=131072

3. Now merge the OpenWrt sysupgrade image and the u-boot into one binary:

$ cat c2v1_uboot.bin openwrt-squashfs-sysupgrade.bin > ArcherC2V1_tp_recovery.bin

• Set your computer's IP to a static 192.168.0.66 address (subnet mask 255.255.255.0 and default gateway to 192.168.0.1).
• To flash the recovery image, start a TFTP server from IP address 192.168.0.66 and serve the recovery image named 'ArcherC2V1_tp_recovery.bin'.
• Connect your device to the LAN port, then press the WPS/Reset button and power it up. Keep pressing the WPS/Reset button for 10 seconds
• The device will try to download the recovery image and flash it. This might take up to 20-25 minutes to finish. When done, the router will reboot itself.
• After reboot, you can access OpenWrt at 192.168.1.1. From here on out, you can simply use sysupgrade with the vanilla OpenWrt images to upgrade.

Similar instructions can be found as posted by OpenWrt forum member yoq here. Old recovery image c2_recovery.zip can be downloaded here.

* These seemingly irregular values are the result of the dynamic mtd splitter resizing the OpenWrt kernel and rootfs 'partitions' as needed. Sizes are extracted from a personalised build, so kernel, rootfs and rootfs_data values may slightly differ on stock OpenWrt builds (and also between 19.07, 21.02 and master e.g.). Other partition sizes should be identical.

See the hardware details tab at the top of the page.

The case is a bit hard to open, start with the two screws. Then start prying the lid from the bottom of the case, starting at the side with the ethernet connectors, There are 11 notches all around keeping the lid in place. They come loose by pushing the bottom part of the case outward.

The Serial connector is labeled 'J2', and is wired as follows. See picture below for the location on the board.

  Ethernet side of PCB
  
     VCC  ... not used.
     GND  -------------- GND of Serial adapter
     RX   <-- input  <-- Tx of Serial adapter
     TX   --> output --> Rx of Serial adapter
     
  Led side of PCB

Where 'RX' connects to the output of your serial adapter, and TX, connects to the input of your serial adapter. You can verify this, by using a volt meter to check that 'TX' pin is at Vcc level, and the RX pin is at GND level. The bootloader of the stock firmware can be interrupted by pressing a digit from 1 .. 7, press '4' for the u-boot prompt. From the serial console, you can login to the running Linux based stock firmware with: username 'admin' and password '1234'.

Soldering

The GND pin may be a bit hard to solder, i needed to scratch away some paint from the PCB to make a large enough connection. On some versions you need to solder 2 bridges to get serial port working. You need good soldering experiences for that!

Board picture (v1)

UART isn't populated, it's indicated by a red rectangle on the picture below (click for bigger size).

The C2 uses a external GBit switch, connected by MDIO bus. Network traffic to the CPU is passed through the internal switch of the MT7620A SoC:

             +---------------+
             |  MT7620A CPU  |
             +---------------+
                      |
                      6 
+----------------------------+
|           MT7620A          |
|       embedded switch      |
+----------------------------+
  unused              5 (RGMII)
  5x FastEth PHY      |
                      |
                      6 (RGMII)
+----------------------------+
|         RTL8367RB          |
|    switch & 5x GBit PHY    |
+----------------------------+
  0     1     2     3     4
  |     |     |     |     |
 WAN   LAN1  LAN2  LAN3  LAN4

Version: 1.1.3 (Dec 4 2013) Ralink UBoot Version 4.1.2.0

MT7620 # bdinfo
boot_params = 0x83F4FFB0
memstart    = 0x80000000
memsize     = 0x04000000
flashstart  = 0x00000000
flashsize   = 0x00800000
flashoffset = 0x00000000
ethaddr     = xx:xx:xx:xx:xx:xx
ip_addr     = 192.168.0.1
baudrate    = 115200 bps

Push '4' to enter UBoot

The following forum threads have been used to discuss the C2:

• https://forum.openwrt.org/viewtopic.php?id=52625
• https://forum.lede-project.org/t/support-for-tp-link-archer-c2-v1/14301

Thanks to everyone that contribute to make this possible.

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