Based on work by naxalite, wth, frontalot, and noName.
Originally by frontalot.
MIPSel LinkStation | Some of these commands have not yet been tested on the mipsel-hdhlan LinkStation. Please report any differences.
The AVR controls much of the LinkStation hardware, including the power button and LED indicator. It is controlled by the commands sent to /dev/ttyS0. To send commands to the AVR:
echo -n "commands" > /dev/ttyS0
|\30\30\30\30||Stops smbd and atalkd if /dev/hda3 is not mounted to /mnt. Sent by /www/script/melsub_diskcheck.sh.|
|[[[[||Starts slowly blinking power LED (sleep).|
|]]]]||High-speed cooling fan rotation.|
|\\\\||Low-speed cooling fan rotation.|
|>>>>||Unknown. Sent by mc_ctld on boot.|
|AAAA||Unknown. Sent by mc_ctld on boot.|
|CCCC||Sent by shutdown -r now (reboot).|
|EEEE||Sent by shutdown -h now (halt).|
|FFFF||Unknown. Sent by mc_ctld on boot.|
|JJJJ||Unknown. Sent by mc_ctld on boot.|
|KKKK||Unknown. Sent by mc_ctld on boot.|
|QQQQ||Unknown. Sent by mc_ctld on set timer.|
|RRRR||End of clear flash memory.|
|SSSS||Start of clear flash memory and /www/script/melsub_init.sh. Sent by /www/script/melsub_flash.sh.|
|TTTT||Flash memory update completed (stops blinking power, disk full, and diagnostic LEDs).|
|UUUU||Flash memory update started (starts blinking power, disk full, and diagnostic LEDs).|
|VVVV||Turns off disk full LED.|
|WWWW||Turns on disk full LED.|
|XXXX||Stops blinking disk full LED.|
|YYYY||Starts blinking disk full LED.|
|ZZZZ||Stops slowly blinking power LED. Sent by mc_ctld.|
|gggg||Diagnostic LED blinks 3 times and system shutdown (partition error).|
|iiii||Diagnostic LED blinks 4 times and system shutdown (cooling fan error).|
|kkkk||Diagnostic LED blinks 5 times and system powers off (flash memory error).|
|mmmm||Diagnostic LED blinks 6 times and system shutdown (hard drive or mc_ctld error).|
|oooo||Diagnostic LED blinks 7 times and system shutdown (RAM, NIC, or HDD controller error).|
Most of this information courtesy of http://www.yamasita.jp/linkstation.en/index.html.