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IPMI(4)                  BSD Kernel Interfaces Manual                  IPMI(4)

     ipmi -- Intelligent Platform Management Interface driver

     ipmi0 at mainbus0

     The ipmi term Intelligent Platform Management refers to autonomous moni-
     toring and recovery features implemented directly in platform management
     hardware and firmware.  The key characteristics of Intelligent Platform
     Management is that inventory, monitoring, logging, and recovery control
     functions are available independent of the main processor, BIOS, and
     operating system.

     Platform status information can be obtained and recovery actions initi-
     ated under situations where vendor "in-band" management mechanisms are
     unavailable.  The independent monitoring, logging, and access functions
     available through IPMI provide a level of manageability built in to the
     platform hardware.  This can support systems where there is no systems
     management software available for a particular operating system.

     At the heart of the IPMI architecture is a microcontroller called the
     Baseboard Management Controller (BMC).  The BMC provides the intelligence
     behind Intelligent Platform Management.  The BMC manages the interface
     between system management software and the platform management hardware,
     provides autonomous monitoring, event logging, and recovery control and
     serves as the gateway between systems management software and hardware.

     IPMI uses message-based interfaces for the different interfaces to the
     platform management subsystems.  All IPMI messages share the same fields
     in the message "payload", regardless of the interface (transport) that
     they're transferred over.  IPMI messaging uses a request/response proto-
     col.  IPMI request messages are commonly referred to as commands.  The
     use of request/response protocol facilitates the transfer of IPMI mes-
     sages over different transports.  IPMI commands are grouped into func-
     tional command sets using a field called network function code.  There
     are command sets for sensor and event related commands, chassis commands
     etc.  This functional grouping makes it easier to organize and manage the
     assignment and allocation of command values.

     Access to monitored information such as temperatures, voltages, fan sta-
     tus etc., is provided via the IPMI Sensor Model.  Instead of providing
     direct access to the monitoring hardware, IPMI provides access by
     abstracted sensor commands such as the "Get Sensor Reading" command,
     implemented via a management controller.  This approach isolates the
     software from changes in the platform management hardware implementation.

     Sensors are classified according to the type of readings they provide
     and/or the type of events they generate.  A sensor can return either an
     analog or discrete reading.  Sensor events can be discrete or threshold-

     The BMC provides a centralized non-volatile System Event Log, or SEL.
     Having the SEL and logging functions managed by the BMC helps ensure that
     post-mortem logging information is available should a failure occur that
     disables the systems processor(s).

     A set of IPMI commands allows the SEL to be read and cleared and for
     events to be added to the SEL.  The common request message (command) used
     for adding events to the SEL is referred to as an Event Message.

     IPMI's extensibility and scalability mean that each platform implementa-
     tion can have a different population of management controllers and sen-
     sors and different event generation capabilities.  The design of IPMI
     allows system management software to retrieve information from the plat-
     form and automatically configure itself to the platform's capabilities.

     Information that describes the platform management capabilities is pro-
     vided via two mechanisms: Capabilities Commands and Sensor Data Records
     (SDRs).  Capabilities commands are commands within the IPMI command sets
     that return fields that provide information on other commands and func-
     tions the controller can handle.

     IPMI defines three standardized systems interfaces that systems software
     uses for transferring IPMI messages to the BMC.  In order to support a
     variety of microcontrollers, IPMI offers a choice of systems interfaces.
     The system interfaces are similar enough so that a single driver can han-
     dle all IPMI system interfaces.

     Keyboard Controller Style (KCS)
             The bit definitions and operation of the registers follows that
             used in the Intel 8742 Universal Peripheral Interface microcon-
             troller.  The term "Keyboard Controller Style" reflects the fact
             that the 8742 interface was used as the legacy keyboard con-
             troller interface in PC architecture computer systems.  This
             interface is available built in to several commercially available
             microcontrollers.  Data is transferred across the KCS interface
             using a per-byte handshake.

     System Management Interface Chip (SMIC)
             The SMIC interface provides an alternative when the implementer
             wishes to use a microcontroller for the BMC that does not have
             the built-in hardware for a KCS interface.  This interface is a
             three I/O port interface that can be implemented using a simple
             ASIC, FPGA, or discrete logic devices.  It may also be built in
             to a custom-designed management controller.  Like the KCS inter-
             face, a per-byte handshake is also used for transferring data
             across the SMIC interface.

     Block Transfer (BT)
             This interface provides a higher performance system interface
             option.  Unlike the KCS and SMIC interfaces, a per-block hand-
             shake is used for transferring data across the interface.  The BT
             interface also provides an alternative to using a controller with
             a built-in KCS interface.  The BT interface has three I/O mapped
             ports.  A typical implementation includes hardware buffers for
             holding upstream and downstream message blocks.  The BT interface
             can be implemented using an ASIC or FPGA or may be built in to a
             custom-designed management controller.

     IPMI provides watchdog(4) timer functionality.  Once configured, if the
     watchdog is not reset within a certain period of time, it will timeout
     and the server will reset.  The reset will occur regardless of the recov-
     erability of the hang or crash.

     Example of enabling a watchdog:

           # sysctl kern.watchdog.period=10

     In this case if the watchdog is not reset, it'll reboot the server after
     roughly 10 seconds.

     Example of disabling the watchdog:

           # sysctl kern.watchdog.period=0

     watchdog(4), sensorsd(8), sysctl(8)

     The ipmi driver first appeared in OpenBSD 3.9 and conforms to the IPMI
     1.5 specification.

     The ipmi driver was written by Jordan Hargrave <jordan@openbsd.org>.

BSD                             March 28, 2017                             BSD