System Management Bus Revision 2.0

Transcription

1 System Management Bus Revision 2.0 Robert Dunstan, Intel Corporation Dale Stolitzka, Analog Devices, Inc.

2 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

3 Why make an SMBus 2.0? Desktop and Server Needs PCI Bus Engineering Change Request

4 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

5 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

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

7 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

8 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) = x 8 + x 2 + x 1 + 1

9 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

10 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

11 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)

12 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

13 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)

14 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!

15 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

16 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

17 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

18 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

19 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

20 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

21 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

22 Call to Action Review and comment on specification to: Work with the SBS-IF to make SMBus 2.0 successful too! Support SMBus in future ACPI OS releases