• Comprehensive device information and various tips&tricks can be found in Hardkernel’s wiki. Please be aware that some of the information does not apply to Armbian (eg. we use a different partition table). Schematics can be found here.
  • Idle consumption with legacy image in headless mode (setenv nographics "1" defined in /boot/boot.ini) and only Gigabit Ethernet connected is between ~2300 mW (@500 MHz) and ~2400 mW (@1536 MHz). Hardkernel provides the possibility to exceed 1536 MHz max cpufreq but Armbian refrains from doing so. In case you want to change settings please keep in mind that you might have to adjust both /boot/boot.ini and /etc/defaults/cpufrequtils.
  • The legacy kernel we use implements a few different cpufreq governors that show partially strange behaviour (interactive most of the times acting like performance for example). Since idle consumption differences between different cpufreq governors are negligible choosing even performance seems to be ok. At least conservative governor that switches between upper and lower clockspeeds (for details see here) leads to some USB performance drops while not providing significant savings. In case you activate higher clockspeeds please keep in mind that switching then to performance governor is needed since otherwise you might end up with a slower system since the added cpufreq operating points will slow down switching to highest clockspeed when needed.
  • If you don’t need GbE network transfer speeds switching to Fast Ethernet with ethtool -s eth0 speed 100 duplex full saves ~230 mW. Completely disabling Ethernet saves an additional 100mW.
  • GbE Ethernet speed should reach 935 Mbits/sec in TX direction. In RX direction with defaults you should get 800 Mbits/sec but with some tuning it should be able to exceed 900 Mbits/sec:
  • echo 32768 > /proc/sys/net/core/rps_sock_flow_entries
  • echo 32768 > /sys/class/net/eth0/queues/rx-0/rps_flow_cnt
  • You can save at least 170mW by cutting power to the internal USB hub (and also all USB devices connected to any of the type A receptacles) using /sys/class/gpio/gpio126 (see description here). The same way you have full control over power consumption of a connected host powered USB disk: umount /mnt/usb && echo 0 >/sys/class/gpio/gpio126/value and echo 1 >/sys/class/gpio/gpio126/value && sleep 2 && mount /mnt/usb
  • Reducing DRAM clockspeed to reduce consumption doesn’t work (difference between default 912 MHz and 408 MHz is just ~100mW less and also requires a reboot)
  • the red led is a power led while the blue led is custom. Boot stage: as soon as u-boot is loaded the blue led lights solid and when kernel starts this changes to heartbeat blinking with default settings. Check cat /sys/class/leds/*blue*/trigger for other functionality.