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SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI System Management Bus Revision 2.0 Robert Dunstan, Intel Corporation Dale Stolitzka, Analog Devices, Inc.
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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System Management BusRevision 2.0
Robert Dunstan, Intel CorporationDale Stolitzka, Analog Devices, Inc.
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Agenda
• Why make an SMBus 2.0--An Overview?• PCI Engineering Change Request• Electrical Specifications
• DC / AC
• Protocol Layer• ARP, the address resolution protocol• Packet Check Coding
• Impact on the SBS IF
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Why make an SMBus 2.0?
• Desktop and Server Needs• PCI Bus Engineering Change Request
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Desktop OEM’s Made TheseComments on SMBus• SMBus has become an extremely popular
bus for connecting low-speed components toeach other
• SMBus attaches these devices• EEPROMs, sensors, latches, monitoring ASICs
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Desktop OEMs Use SMBus...
• Configuration or Inventory Applications• DIMMs/RIMMs Memory Modules• Clock Generators• Identify a Slot 2 Processor by Type and Speed• EEPROM contain vital product data• Digital Potentiometers
• System Monitoring• Temperature Monitors• Fan Control• Environmental Monitoring• Security
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SMBus Devices in Systemsthat are in Production Today• Memory DIMMs (3 EEPROMs)• ISC 9179 clock generation control• Inventory for Slot 2 Processor Type/Speed• EEPROM for vital product data• Voltage/Fan monitoring, e.g., ADM9240
• Processor Temperature , e.g., ADM1021
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Electrical Specifications, v2.0
• New DC Electrical specifications allow:• Driving SMBus signals through PCI connector• Multiple loads on a planar (motherboard)• Suitable for desktop and mobile environments
• AC specifications include some noiseimmunity tolerance from DC to 10MHz
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Protocol Layer Outline
• ARP (Address Resolution Protocol)• An ARP is the ability for a device to accept a new
SMBus address through a sequence ofcommands
• ARP commands in the command set• Other commands outside of the ARP
• Hot-plug issues• Packet check coding is required
• CRC-8: C(x) = x8 + x2 + x1 + 1
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SMBus 2.0 ARP
• Needs of SMBus devices on PCI cards aredifferent from motherboard components:• No past knowledge of devices (address/types)• Similiar PCI cards can result in several device of
the same type plugging into the PCI bus• SMBus ver 2.0 requires PCI card devices to
accept new bus addresses
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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SMBus 2.0 AddressResolution Protocol Highlights• Notification
• Devices may request enumeration on power-up
• Discovery• OS can discover devices
• discover and identify devices• assign addresses and access the devices
• Other entities can discover devices• Secondary hosts can discover devices on the bus
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Hot-plug & SMBus
• Servers hot-plug PCI cards so that new orreplacement cards do not interrupt service
• Mobile systems hot-plug into a dock• SMBus is appropriate for hot-plugging
• Bus is being hot-plugged for batteries• However, there are complex power-up issues
• ECR plans to use existing PCI quick switches• Servers may use SMBus when the PCI is not
operating (a sideband to the PCI bus)
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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AOL use of SMBus
• Current AOL (Alert-On-LAN) implementationsare geared towards LOM (LAN OnMotherboard) solutions• Not friendly if using only the PCI connector
• SMBus is viewed as an interface betweenalert generators and the LAN controller• Unfortunately the NIC (Network Interface Card)
solution is not satisfactory
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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A solution for NICs
• Need for a cable-less solution for the NIC• Don’t want to repeat the mistakes learned
from Wake On LAN• Initial WOL implementations required a cable
between NIC and the motherboard for wake signaland Vaux power
• Later added PME and 3.3Vaux to the PCI Spec• AOL needs outbound communication even when the OS
is absent. (PME is an inbound signal)
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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PCI ECR for Adding SMBus
• Effort championed by Compaq, Intel and IBM• Assistance from Analog Devices, Philips, USAR,
3Com
• ECR currently in review by the PCI SIG
• ECR defines SMBus clock and data signalson PCI connector using two reserved pins• Discovery mechanism required!
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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SMBus Device Discovery
• Existing SMBus specifications do not addressenumeration or dynamically assigned deviceaddresses
• SMBus 2.0 defines an Address ResolutionProtocol (ARP) which provides thesecapabilities
• ARP includes a data structure much like PCIconfiguration space and a unique identifier
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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More Uses--SMBus over PCI
• Provides the physical backbone for IPMI(Intelligent Platform Management Interface)
• Allows intelligent adapters to enumeratemanageability and instrumentation devices
• Related interfaces (AGP, Mini PCI) to followthe PCI lead
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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SMBus 2.0 Timeline
• ARP definition 80% complete• Electrical additions to support PCI ECR are
90% complete• 0.9 spec available for public review in April• PCI ECR ratification expected in 2Q99
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Summary
• Industry needs an SMBus solution today• SBS IF has developed an interim solution• SMBus is not just a battery bus• The SMBus is still evolving
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Impact on the SBS IF (1)
• New influence from Desktop systems• New influence from Server systems• Many problems being solved with the SMBus
different from the original [mobile] vision
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Impact on the SBS IF (2)
• Effect on the SBS IF is very positive• Broader endorsement of SMBus• More volume and standardization will lead to
more vendors, wider device selection, moreparticipation in the IF
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Conclusions
• SMBus continues to evolve• ARP adds flexibility• Electrical changes make SMBus more usable
on motherboards• Wider influence establishes SMBus as very
important to the PC industry
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI
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Call to Action
• Review and comment on specification• email to: [email protected]
• Work with the SBS-IF to make SMBus 2.0successful too!
• Support SMBus in future ACPI OS releases
