Designing with SMBus 2.0 - SBS-IF Smart Battery System ...

Designing with SMBus 2.0Dale StolitzkaAnalog Devices, Inc.January 29, 2001SBS-IF Winter Workshop

AcknowledgementsMaterials and content for this presentation has beencompiled from a variety of SMBus sub-committeemembers. The author wishes to acknowledge andthank contributors: Steve Williams, Cliff Laney andJohn Milios for their efforts on the development of theSMBus 2.0 specificationSBS-IF Winter Workshop

Agenda• Problem Statement• SMBus on PCI and mini-PCI connector• SMBus Addressing Problem & ARP• Physical Layer – AC & DC Changes• Packet Error Checking Review• Impact on SMBus 1.0 & 1.1• SummarySBS-IF Winter Workshop

RProblem Statement• SMBus allows signaling between PCcomponents• Pre-boot or when OS is down• When the PCI bus is unavailable• OEMs demand SMBus signaling onexpansion cards• Pig-tails are bad• How do we use SMBus on PCI?SBS-IF Winter Workshop

SMBus on the PCI and mini-PCI Connector• Specified in the SMBus 2.0 spec and inan ECR to the PCI 2.2 specification• SMBus uses 2 pins on the connector• More robust electrical specifications• Plug ‘n Play capability to resolve SMBusaddresses• Address Resolution Protocol (ARP)SBS-IF Winter Workshop

SMBus Addressing Problem• SMBus devices require a bus address• Old model used fixed addresses• Expansion cards require dynamicallyassigned addresses• Avoid conflicts with addresses used bymotherboard devices• Allow for multiple boards of the same typeSBS-IF Winter Workshop

Address Resolution Protocol (ARP)• Every SMBus device has a UniqueDevice ID (UDID)• fixed or random• At start time, the bus is enumerated• Some devices may be fixed onmotherboard• Addresses are assigned to allenumerated devicesSBS-IF Winter Workshop

ARP in the System• An ARP Agent may run ARP:• Software running over a host controller• Microcontroller running independently• The bus may be enumerated at anytimewithout address assignment• Software makes address map availableto appsSBS-IF Winter Workshop

Unique Device Identifier8 bits 8 bits 16 bits 16 bits 16 bits 16 bits 16 bits 32 bitsDeviceCapabilitiesVersion /RevisionVendor ID Device ID InterfaceSybsystemVendor IDSubsystemDevice IDVendor-Specific IDMsbLsb• Device Capabilities = specific functions, e.g., supports PEC• Version/Revision = silicon revision, SMBus UDID version• Vendor ID = device manufacturer’s vendor ID• Device ID = device ID assigned by manufacturer• Interface = SMBus version of this device• Subsystem Vendor ID = interface ID for industry group• Subsystem Device ID = device ID for industry group• Vendor-specific ID = 0x00000000 for SMBus 1.xensures a unique UDID in SMBus 2.0SBS-IF Winter Workshop

How UDID is Used in Segment/Device InfoSMB_INFO StructureSMB_INFO Struc VerSMB_INFO Struc VerSMBus Spec VersionSMBus Spec VersionSegment HW CapabilitySegment HW CapabilityReservedReservedDevice CountDevice CountDevice 0 InfoDevice 0 InfoDevice 1 InfoDevice 1 Info…Device n InfoDevice n InfoHC supports PECSMB_Device StructureSlave AddressSlave AddressReservedReservedDevice UDIDDevice UDIDSlave device supports PECSMB_UDID StructureDeviceDeviceHWHWCapabilitiesCapabilitiesVersion/RevisionVersion/RevisionVendorVendorIDIDDeviceDeviceIDIDInterfaceInterfaceSubsystemSubsystemVendorVendorIDIDSubsystemSubsystemDeviceDeviceIDIDReservedReservedSBS-IF Winter Workshop

Example of an ARP Agent• Performs ARP process• Build assigned address pool• Assigns addresses to SMBus 2.0 devices• ARP agent may run when…• SMBus driver initializes• Hot insertion / PnP notification received• Resume notification• ‘Notify ARP Master’ from SMBus HC (requires HCinterrupt support)SBS-IF Winter Workshop

Building the Assigned AddressPool_SBI control method inSMBus CMI 1.0 Spec+Fixed Slave AddressesReserved Address AssignmentsARP Assigned AddressesAssigned Address PoolAppendix ‘C’ inSMBus 2.0 SpecObtained byrunning ARPSBS-IF Winter Workshop

Selecting ARP Slave AddressesRules:• Retain the same slave address if at all possible• Honor slave address preferences if possible• For new devices assign unused slaveaddresses first• Recycle ‘pre-owned’ slave addresses only as alast resortSBS-IF Winter Workshop

Physical Layer Features• SMBus 2.0 is designed to be backwards1.x 2.0compatible• Bus rate is the same• Two DC power classes• Low-power class ➯ SMBus v1.1 limits• New high-power class ➯ SMBus v2(these work on SMBus 1.x systems)SBS-IF Winter Workshop

AC Data Rate≤100µs may be ≥100µsSMBCLKSMBDAT7 6 5 4 3 2 1 0 A/A• Not really, they refer to different issues• Periodic clock stretching: F SMB α data rate of typicaldata bits• Random clock stretching: T LOW:SEXT is the total timea slave device may stall the busSBS-IF Winter Workshop

AC Rise/Fall Timing• DC levels for t RISE , t FALL are symmetricrather than dependent on V DD0.9 × V DD5VV IH,MIN + 0.15VV IL,MAX - 0.15VV DD3Vt FALL,2.0t RISEt FALL,1.xSBS-IF Winter Workshop

Recommended host controllerdetection 3σ toleranceAC TimeoutRecommended device driverT TIMEOUT 3σ tolerance25 ms2.5 msspecification window35 ms• T TIMEOUT clarified, not changed• Devices timeout after SMBCLK is low for 25ms• Host controllers must support T TIMEOUTSBS-IF Winter Workshop

DC New High-power Class• C BUS ≤ 400pF• ~11x larger than low-power class• I PULLUP ≥ 4mAV DDSMBusDeviceR SI PULLUPorR PULLUPR DSC BUSSMBusHostOptionalESDprotectionSBS-IF Winter Workshop

DC Back-powering• Unpowered devices must not load thebus or power-up devices• I LEAK-PIN ≤ 10µA• relaxed from SMBus v1.xPinSBS-IF Winter Workshop

Packet Error Checking…AMSG ByteAPEC ByteAP• PEC (Packet Error Code) byte appends tomessage• Uses CRC-8 polynomial: C(x) = x 8 + x 2 + x + 1• Required for Address Resolution ProtocolSBS-IF Winter Workshop

PEC implementationWrite Byte/Word/BlockS Slave Address W A Command Code A...Data ByteAPS Slave Address W A Command Code ACRC-8APRead Byte/Word/BlockS Slave Address W ACommand CodeACRC-8 is calculated uponthe whole messageincluding Address and R/W bitS Slave Address R A Data Byte A...Data ByteAData providedby slave receiverData providedby master transmitterCRC-8NAPSBS-IF Winter Workshop

Error Recovery• Specifies the use of ACK, NAKsignaling for flow control and errorrecovery in bus transactions• Different than I 2 C• I 2 C specifies that you can ACK/NAK thefollowing byte• Works in conjunction with CRC-8SBS-IF Winter Workshop

ACK and NAK usageS Slave Address W A Command Code ACRC-8A…A NAK by the Slave Receiverduring a Write operationbefore the last byte is interpretedas a transaction ABORT (busy, overflow,unknown command, etc.)A NAK by the SlaveReceiver atthe CRC-8 bytemeans RESENDS Slave Address R A Data Byte A CRC-8 NA PThe Master Receiver detecting an error in the Packet Check Code,terminates the transaction and repeats the operationSBS-IF Winter Workshop

Hardware PEC Generator7 6 54 3 210b• CRC is C(x) = x 8 + x 2 + x + 1• Simple hardware-generated PEC forhardware-based ASICSBS-IF Winter Workshop

PEC with Intelligent Targets• Intelligent targets (µC) recover errors inother layers• Last ACK ⇒ PEC byte received• Allows µC core to calculate CRC-8 withoutstalling the SMBCLK• More IC selection to OEMThis devices ishereby permittedto recovererrors inclever ways byvirtue of itsextraordinaryintelligence.SBS-IF Winter Workshop

PEC & Intelligent Target HardwarePEC A PNAK means PEC is bad in eitherSMBus 1.1 or SMBus 2.0IntelligenttargetACK means PEC is valid in SMBus 1.1An ACK by an intelligent SMBus 2target means the PEC is received butmay defer error recovery to a higherprotocol layerSBS-IF Winter Workshop

ExampleSensors and Add-in Targets• Targets on the motherboard• Hardware monitors, EEPROM, etc.• Don’t need a programmable address• May participate in ARP Discovery• Targets on add-in cards• Must ARP & accept address assignmentsSBS-IF Winter Workshop

ExampleChipset• Use a STOP bit for message aborts• Host must watch for slave timeouts• Use error checking whenever possibleSBS-IF Winter Workshop

ExampleHost/Master clearing the bus• Host detects timeout• Send Stop condition• Is the bus clear?• if SMBDAT is still low• Clock the bus untilSMBDAT is high 2HostSlaveM/B sensoror EEPROMSBS-IF Winter Workshop

Impact on SMBus 1.0 &1.1• SMBus 1.0 & 1.1 are SMBus 2.0compliant• No current part becomes obsolete• May be used in current applications• In Smart Batteries and motherboard sensors• SMBus 1.0 and 1.1 parts may not beused on PCI expansion cards• ARP and high-power electricals required onPCI and mini-PCI boardsSBS-IF Winter Workshop

Summary• SMBus 2.0 is designed to be backwardscompatible• SMBus 2.0 can be used on add-in cards anddown on the motherboards• ARP introduced for v2.0 which requires PEC• Some changes in AC and DC from SMBus 1.1• SMBus 2.0 is released and available, nowSBS-IF Winter Workshop

Collateral• SMBus website: http://www.smbus.org• All SMBus specs, 1.0, 1.1, 2.0, SMBusDevice Driver External ArchitectureSpecification, SMBus Control MethodInterface Specification:http://www.smbus.org/specs/index.html• PCI SIG website: http://www.pcisig.com• SMBus ECR to PCI 2.2 Specification• check Members area on PCI SIG websiteSBS-IF Winter Workshop

Call to Action• Device vendors:• Implement SMBus 2.0; For legacy devices, planUDIDs• BIOS vendors:• Implement control methods• System OEMs:• Build SMBus 2.0 into systems now!• wire all PCI slots for SMBus 2.0• Card vendors:• Add SMBus 2.0 to cards where it makes senseSBS-IF Winter Workshop

Example of an SMBus 2.0 Driver Architecture †SmartBatteryStackSMBus TestApplicationOtherSMBusConsumersPnPnotificationRing 3Ring 0SMBusDriverSMBus Class Driver(SMBCMICL.SYS)SMBus CMI Miniport(SMBCMIHC.SYS)AddressResolutionProtocol(ARP) AgentINF File(SMBCMIHC.INF)AssignedAddress PoolRing 0ACPIACPIHardwareSMBus CMI ObjectName(_HID, "SMBUS01")Name(_UID, 0)_SBI() // Information_SBR() // Read_SBW() // Write_SBT() // Transfer_SBA() // AlertsSMBus CMI ObjectName(_HID, "SMBUS01")Name(_UID, 1)_SBI() // Information_SBR() // Read_SBW() // Write_SBT() // Transfer_SBA() // AlertsECPIIX4/ICHSmart BatterySMBusSMBusAlert on LAN PCI:Heceta PCI NIC 2/3/4 Card w/ ARPable SMBus deviceSBS-IF Winter Workshop