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CHAPTER 3. IPMI INTERFACES

3.2.1 SMIC

The SMIC interface has been around a long time, but mostly during a period when IPMI was not popular. This is a low-performance, byte-at-a-time interface with no interrupt capability. TBD - describe this interface in detail

3.2.2 KCS

The KCS interface is currently the most popular IPMI system interface. The KCS interface looks electrically much like a standard PC keyboard interface. It was chosen because lots of cheap hardware was available for these types of interfaces. But it is still a byte-at-a-time interface and performs poorly. It has the capability for interrupts, but very few systems have working interrupt capability with KCS interfaces.

TBD - describe this interface in detail

3.2.3 BT

The BT interface is the best interface for IPMI. Messages are sent a whole message at a time through the interface, thus it is a much higher performance interface than the other system interfaces. TBD - describe this interface in detail

3.2.4 SSIF

The SSIF interface was added in the 2.0 spec. It provides an interface over an Inter Integrated Circuit (I2C) interface using the SMBus protocol. This is very cost effective interface; most systems generally already have an I2C bus, so no new interfaces to processor busses are required. However, I2C busses are not very fast and the interfaces from the processor to the I2C bus tends to perform poorly.

TBD - describe this interface in detail

3.2.5

The

OpenIPMI

Driver

The OpenIPMI driver on Linux provides a user interface to all the standard IPMI system interfaces. It does so in a manner that allows multiple users to use the driver at the same time, both users in the kernel and users in user space.

To do this, the OpenIPMI driver handles all the details of addressing and sequencing messages. Other drivers allowed more direct access to the IPMI interface; that means that only one user at a time could use the driver. Since the IPMI can be used for different purposes by different users, it is useful to do the multiplexing in the kernel.

The details of configuring the IPMI driver are found in the IPMI.txt file in the kernel documentation; those details won’t be discussed here.

To use the IPMI device driver, you open the /dev/ipmi0 or /dev/ipmidev/0 file. The driver allows multiple IPMI devices at the same time; you would increment the number to get to successive devices. However, most systems only have one.

The primary interface to the driver is through ioctl calls. read andwrite calls will not work because the IPMI driver separates the addressing and data for an IPMI message.

The core description of an IPMI message is:

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