Here is brief overview of it's configuration:
CPU: Rockchip RK3288 - Quad core ARM cortex A17 @ 1.8GHz
eMMC: 4GB - for OS
Storage: 16GB μSD card in internal slot
On FW version 2.7 it's running kernel 4.9.174 build with buildroot.
Photos of internals:
On the CPU board is populated 4 pin header (on picture is connected) with UBoot/OS serial console living on it. Pinout is GND, RX, TX, 3V3. After connecting and powering device up you can enter UBoot bootloader or system after. Login name is root and no password is needed. From Uboot you can boot system or enter fastboot mode for flashing system image. Whole system partition is read only and for any modifications it's needs to be remounted.
By default authorized_keys is key:
cert-authority ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQDHbFTQuU+WZRuYN488WRuUfvalnA9HbNNyMd8TIMlThQXiID1Au15erQ820iYS+yczQv9Fpkq3epubs31QA1bN/a+S0cTJcEIw8FUAcowN9BEu8DR5/ZqK0iHb/1VbpiQ+raaO2vz4MmcrVlJCQBqALH08kJB54OSFmUwQmqDvxelkOpzG450cNy
So let's add our own ssh pubkey!
In order to do that we need to log to device, remount / as RW
mount -o remount,rw mmcblk2p6
Then edit /etc/ssh/sshd_config →
Uncomment PubkeyAuthentication yes
Comment UsePAM yes
Comment UsePrivilegeSeparation sandbox
Then add our ssh pubkey to ~/.ssh/authorized_keys
Run sshd with /sbin/sshd
Now set automatic run of sshd at start → currently I'm not able to run sshd service after boot I solved this by installing inside ESP8266 which act as serial to telnet bridge over WiFi.