AVM FRITZ!Box 4020

AVM FRITZ!Box 4020

Everything is working, except for the USB port. The root hub reports having zero ports.

ModelVersionSoCCPU MHzFlash MBRAM MBWLAN HardwareWLAN2.4WLAN5.0100M portsGbit portsModemUSB
FRITZ!Box 4020Qualcomm Atheros QCA956175016128Qualcomm Atheros QCA9561b/g/n-5--1x 2.0

OpenWrt can be installed via the EVA bootloader. The EVA bootloader waits in the first 5 seconds after power-on for an FTP connection on Set your IP address to and upload the image like following.

ftp -n -4

  ftp> quote USER adam2
  ftp> quote PASS adam2
  ftp> binary
  ftp> debug
  ftp> passive
  ftp> quote MEDIA FLSH
  ftp> put openwrt-sysupgrade.bin mtd1

The process can take up to 3 minutes. After a minute, the INFO LED will illuminate Red. Once the LED turns off the process is complete and you need to powercycle to boot up OpenWrt.

AVM GPL code can be found on their FTP.

In case you are using the AVM provided recover.exe, a counter on the tffs partition will increment. It is located at 0x7AE and labeled as recovered. It currently does not seem to be incremented by the Installation methods mentioned in the next section.

To revert back to the AVM stock-firmware, you need to download the image provided on their ftp (ending in .image).

Rename the downloaded file from xyz.image to xyz.tar and extract the archive. In the /var/tmp subdirectory you find a kernel.image file. Flash it like the above described process for OpenWrt installation, use the kernel.image in the last step.

SoC Qualcomm QCA9561 (Dragonfly) 720MHz
RAM 128MB (Winbond W971GG6KB-25)
Flash 16 MiB SPI-NOR (Macronix MX25L12835F)
WiFi Qualcomm QCA9561 3×3 b/g/n
Bootloader ADAM2/EVA
Ethernet 4 x 100 Mbit/s LAN / 1 x 100 Mbit/s WAN
USB 1x USB 2.0
Serial console onboard

There seem to be two different antenna layouts. One with all three antennas parallel and an other layout where two antennas are parellel and one is orthogonal. See images below:

Two antennas are parellel, one is orthogonal.

All three antennas are parallel.

Serial pinout is described here. Don't connect to 3.3V! Set to 115200N8 for connection.

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  • Last modified: 2019/10/02 06:48
  • by tmomas