Watching the CPU usage real time it spikes more than the graphing shows. I was downloading some large files yesterday which is the large spikes in bandwidth and CPU, but beside that, it doesn't really go that high.
The watchdog timer on RB products are all hardware watchdog timers, the CPU can be hard locked and the watchdog timer will still reboot the board. The RB software has to keep poking at the watchdog timer located in a PLD before expiry or it will reboot the CPU or the PLD is doing the querying, not really sure.
So, what could be the cause?
Hard to diagnose. Check the settings like SNMP on routerboard OS seems quite flakey and can drive the CPU to 100% for no good reason. off site logging can help. Are you using the "UP" part of the board to power the ubnt access points or using the included injector?
Turning it off will likely stop your problem, but one of the things I love about routerboards is the hardware watchdog and has saved me a few late night power cycles.
You can use any public NTP server to set the time on an RB.
Verify that your Ethernet cables are good. I had one with a short and when I tried to POE over it the 750 would reboot.
Check the Routerboot is current for the Version of OS you're running. Version 5+ Click System > Routerboard. Check the Current Firmware and Upgrade Firmware are the same. If not upgrade and reboot. Version Routerboard>Settings
Check the Power supply is strong enough if you are using the POE output. Maybe think about swapping the Power Supply with another one.
And last option which has actually worked for me a few times. Reset to defaults and program it again.
NOTE that If you turn off the watchdog timer, whatever it is that's causing it to halt and reboot will probably not stop happening, and you will have disabled the ability of the hardware to reboot itself.... which means you will have to power cycle it manually.
