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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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6 Desktop OEM’s Made These Comments on SMBus • SMBus has become an extremely popular bus for connecting low-speed components to each other • SMBus attaches these devices • EEPROMs, sensors, latches, monitoring ASICs
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI % )'YR DD -DSDQ 'HY&RQ ,) 6%6 SMBus Devices in Systems that 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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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 noise immunity tolerance from DC to 10MHz
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI % )'YR DD -DSDQ 'HY&RQ ,) 6%6
Protocol Layer Outline
• ARP (Address Resolution Protocol) • An ARP is the ability for a device to accept a new SMBus address through a sequence of commands • 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
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI % )'YR DD -DSDQ 'HY&RQ ,) 6%6
SMBus 2.0 ARP
• Needs of SMBus devices on PCI cards are different 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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6 SMBus 2.0 Address Resolution 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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
Hot-plug & SMBus
• Servers hot-plug PCI cards so that new or replacement 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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
AOL use of SMBus
• Current AOL (Alert-On-LAN) implementations are geared towards LOM (LAN On Motherboard) solutions • Not friendly if using only the PCI connector • SMBus is viewed as an interface between alert 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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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 signal and 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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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 signals on PCI connector using two reserved pins • Discovery mechanism required!
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI % )'YR DD -DSDQ 'HY&RQ ,) 6%6
SMBus Device Discovery
• Existing SMBus specifications do not address enumeration or dynamically assigned device addresses • SMBus 2.0 defines an Address Resolution Protocol (ARP) which provides these capabilities • ARP includes a data structure much like PCI configuration space and a unique identifier
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI % )'YR DD -DSDQ 'HY&RQ ,) 6%6
More Uses--SMBus over PCI
• Provides the physical backbone for IPMI (Intelligent Platform Management Interface) • Allows intelligent adapters to enumerate manageability and instrumentation devices • Related interfaces (AGP, Mini PCI) to follow the PCI lead
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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, more participation in the IF
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI % )'YR DD -DSDQ 'HY&RQ ,) 6%6
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 % )'YR DD -DSDQ 'HY&RQ ,) 6%6
Call to Action
• Review and comment on specification • email to: [email protected] • Work with the SBS-IF to make SMBus 2.0 successful too! • Support SMBus in future ACPI OS releases
SMBus Revision 2.0 R. Dunstan, Intel and D. Stolitzka, ADI