Asus RS100-E8-PI2 - Manual (Page 58)

Chapter 4: Motherboard information 4-6
4. CPU Warning LED (ERR_CPU1)
The CPU warning LED lights up to indicate that a CPU error or failure has occurred.
5. Baseboard Management Controller LED (BMC_LED1)
The green heartbeat LED blinks per second to indicate that the ASMB7 is working
normally.