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IMCSMB(4)	       FreeBSD Kernel Interfaces Manual		     IMCSMB(4)

     imcsmb -- Intel integrated	Memory Controller (iMC)	SMBus controller

     device pci
     device smbus
     device imcsmb

     Alternatively, to load the	driver as a module at boot time, place the
     following line in loader.conf(5):


     The imcsmb	driver provides	smbus(4) support for the SMBus controller
     functionality in the integrated Memory Controllers	(iMCs) embedded	in In-
     tel Sandybridge-Xeon, Ivybridge-Xeon, Haswell-Xeon, and Broadwell-Xeon
     CPUs.  Each CPU implements	one or more iMCs, depending on the number of
     cores; each iMC implements	two SMBus controllers (iMC-SMBs).  The iMC-
     SMBs are used by the iMCs to read configuration information from the
     DIMMs during POST.	 They may also be used,	by motherboard firmware	or a
     BMC, to monitor the temperature of	the DIMMs.

     The iMC-SMBs are not general-purpose SMBus	controllers.  By their nature,
     they are only ever	attached to DIMMs, so they implement only the SMBus
     operations	need for communicating with DIMMs.  Specifically:

	   -   READB
	   -   READW
	   -   WRITEB
	   -   WRITEW

     A more detailed discussion	of the hardware	and driver architecture	can be
     found at the top of sys/dev/imcsmb/imcsmb_pci.c.

     As	mentioned above, firmware might	use the	iMC-SMBs to read DIMM tempera-
     tures.  The public	iMC documentation does not describe any	sort of	coor-
     dination mechanism	to prevent requests from different sources -- such as
     the motherboard firmware, a BMC, or the operating system -- from inter-
     fering with each other.

     Therefore,	it is highly recommended that developers contact the mother-
     board vendor for any board-specific instructions on how to	disable	and
     re-enable DIMM temperature	monitoring.

     DIMM temperature monitoring should	be disabled before returning from
     imcsmb_pci_request_bus(), and re-enabled before returning from
     imcsmb_pci_release_bus().	The driver includes comments to	that effect at
     the appropriate locations.	 The driver has	been tested and	shown to work,
     with only that type of modification, on certain motherboards from Intel.
     (Unfortunately, those modifications were based on material	covered	under
     a non-disclosure agreement, and therefore are not included	in this
     driver.)  The driver has also been	tested and shown to work as-is on var-
     ious motherboards from SuperMicro.

     The smb(4)	driver will connect to the smbus(4) instances created by
     imcsmb.  However, since the IMC-SMBs are not general-purpose SMBus	con-
     trollers, using smbmsg(8) with those smb(4) devices is not	supported.

     jedec_dimm(4), smbus(4)

     The imcsmb	driver first appeared in FreeBSD 12.0.

     The imcsmb	driver was originally written for Panasas by Joe Kloss.	 It
     was substantially refactored, and this manual page	was written, by
     Ravi Pokala <>

FreeBSD	13.0			 March 2, 2018			  FreeBSD 13.0


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