X3T9.2/90-178 SCSI Hot Plugging Requirements Roger Dimmick (IBM) 10/18/90 1. DEFINITION OF TERMS 1.1 CONCURRENT MAINTENANCE: Implies that the system is active performing work while the maintenance activity is occurring. Does not necessarily mean that either the elements being inserted/removed from the system are under power or that the logical interfaces to which the insertion/removal activity is forming/breaking connections are active. 1.2 HOT PLUGGING: Implies that the system is active and performing work while the maintenance activity is occurring, and that power is applied at the device interface during the insertion/removal. 1.3 LIVE PLUGGING: Implies that the system is active and performing work while the maintenance activity is occurring, and that power is applied at the device interface during the insertion/removal, and that the logical interface during the insertion/removal is active. 1.4 POWER INTERFACE: An interface independent of SCSI which is used to feed energy to the device to enable its functionality. May include on/off control as well as sequencing, voltage sources, and ground return. 1.5 LOGICAL INTERFACE: That interface which manages the activity of the device and which enables the device to function within the context of the system usage definition. 1.6 QUIESCE: Bring to a stable state, a state in which no transient activity will be recognized as a change in state until commanded by an external mechanism to resume. 1.7 INRUSH CURRENT LIMIT: The elimination/prevention of sources of current which exceed the upper limit of the power system capability without declaring a fault detected state. 1.8 SIGNAL DEBOUNCE: That circuit which precharges the interface line level to the existing level of the interface prior to making the interface connection. 1.9 CONNECTION PIN MANAGEMENT: Assumes separate power connector from the SCSI Connector. Assumes Power Connector pins can be made to engage prior to SCSI Connector pins. The ideal mating sequence is: power ground; SCSI ground; SCSI signal (including TERMPWR); Voltage Levels (+5 Volt level, +12 Volt level) 2. CONCURRENT MAINTENANCE REQUIREMENTS 2.1 QUIESCE SCSI BUS: Complete all actively requested transfers started by any initiator to insure that no other nodes on the bus have reason to participate in the arbitration cycle than the initiator. If greater than a single initiator is present on the bus, some method must be provided between the initiator's to quiesce all except the initiator which acts as master at power on. An acceptable alternative to the foregoing is to provide additional checking to insure the detection of errors which may result from the plugging/unplugging occurrences on the SCSI bus. 2.2 CONNECTOR PIN MANAGEMENT: Minimum requirement is power ground must make prior to signal, and SCSI signal and SCSI ground must make prior to voltage levels. 3. HOT PLUGGING REQUIREMENTS 3.1 QUIESCE SCSI BUS: Complete all actively requested transfers started by any initiator to insure that no other nodes on the bus have reason to participate in the arbitration cycle than the initiator. If greater than a single initiator is present on the bus, some method must be provided between the initiator's to quiesce all except the initiator which acts as master at power on. 3.2 INRUSH CURRENT LIMIT: Circuitry to reduce the rate of charging and or elimination of load characteristics which require charging of significant reactive loads is necessary to prevent the perception by the system power system that it is working into a direct short, in which case, it should turn itself off. 3.3 CONNECTOR PIN MANAGEMENT: Minimum requirement is power ground must make prior to signal, and SCSI signal and SCSI ground must make prior to voltage levels. 4. LIVE PLUGGING 4.1 QUIESCE SCSI BUS: Complete all actively requested transfers started by any initiator to insure that no other nodes on the bus have reason to participate in the arbitration cycle than the initiator. If greater than a single initiator is present on the bus, some method must be provided between the initiator's to quiesce all except the initiator which acts as master at power on. 4.2 INRUSH CURRENT LIMIT: Circuitry to reduce the rate of charging and or elimination of load characteristics which require charging of significant reactive loads is necessary to prevent the perception by the system power system that it is working into a direct short, in which case, it should turn itself off. 4.3 DEBOUNCE CIRCUIT: Because it is not possible to predict the state of the SCSI interface in this condition, it is required that any errors which are introduced to the data stream be detectable. Simple byte wide parity is not adequate, and it is necessary to add some form of Longitudinal Record check, or Cyclic Redundancy Check information to the data stream. For those systems where data error recovery by means of resend is not acceptable due to loss of available bandwidth, it may be necessary to add Forward Error Correction supporting algorithms to the data stream. 4.4 CONNECTOR PIN MANAGEMENT: Minimum requirement is power ground must make prior to signal, and SCSI signal and SCSI ground must make prior to voltage levels.