Baseboard Management Controller ( BMC )

What is a Baseboard Management Controller or BMC?

BMC is a small computer that sits on virtually every server motherboard.
The BMC is usually an Arm-based SoC with graphics and control logic built-in.
Here is an Emulex Pilot 3 diagram on how the BMC hooked into the Intel chipset on an Intel S1200V3 motherboard.


Here is the official ASPEED AST2500 system diagram:

• I2C/IPMB：跟其他Chip溝通使用，像是下command給Hardware monitor取得溫度資料
• Uart/COM port：主要用於跟MCU, Expander溝通
• LAN：主要是讓使用者可以透過這個介面來存取BMC的資料

The BMCs can utilize either shared or dedicated NICs for remote access. They also have multiple connections to the host system providing the ability to monitor hardware, flash BIOS/ UEFI firmware, give console access via serial or physical/ virtual KVM, power cycle the servers, and log events.
BMC is similar to a small Raspberry Pi type device that sits in a server in order to control the larger server.

Why are Baseboard Management Controllers or BMCs Used in Servers?

Baseboard management controllers are used in servers to perform the tasks that an administrator would otherwise need to physically visit the racked server to accomplish:

• power cycling a server
• monitoring fan speeds/ component temperatures, and hardware failures.

Many enterprise BMCs include iKVM（keyboard, video, mouse ）functionality.
可利用獨立於作業系統與跨平台的介面來監控伺服器系統（例如溫度、電壓與風扇狀態）。MIS 人員可透過即時事件通知隨時隨地瞭解伺服器的運作狀態。
Different types of sensors built into the computer system report to the BMC on parameters such as temperature, cooling fan speeds, power status, operating system (OS) status, etc. The BMC monitors the sensors and can send alerts to a system administrator via the network if any of the parameters do not stay within pre-set limits, indicating a potential failure of the system.

OpenBMC is a Linux Foundation Collaborative open-source BMC project.

IPMI ( Intelligent Platform Management Interface )

IPMI defines a set of interfaces used by system administrators for out-of-band management of computer systems and monitoring of their operation.
An IPMI sub-system consists of a BMC and other management controllers distributed among different system modules that are referred to as satellite controllers. The satellite controllers within the same chassis connect to the BMC via the system interface called Intelligent Platform Management Bus/Bridge (IPMB) – an enhanced implementation of I²C (Inter-Integrated Circuit).

The BMC manages the interface between system-management software and platform hardware.