the PCI Bus demystified phần 9

PCI Bus Demystified system slot in Segment B may be used for a peripheral card. Note that the physical size of the PCI bridge chip dictates that the pallet bridge board span several slots. The configuration in the previous slide could be easily extended to accommodate a third Segment C. However, the problem with that approach is that transactions targeted at Segment C would have to pass through two bridges incurring latency in each one. It would be preferable to position the host processor so that it could bridge directly to each of the other segments. Figure 9-10 shows a solution to that problem utilizing pallet bridge boards. The host processor resides in the system slot of Segment B and bridges directly to Segments A and C. Note that Segment A must have its system slot on the right and that two different bridge boards are required—one that bridges from right to left and another that bridges from left to right. In practice, the same PC board can be used for both forms with different mounting locations for the connectors. The same strategy can be implemented with front-loading bridge modules. At least one vendor (Teknor) currently offers a dual-wide SBC that incorporates the bridge function. Segment A Segment B Segment C “Left-hand” Bridge “Right-hand” Bridge Figure 9-10: CPCI bridging of three segments. 164 CompactPCI Summary CompactPCI is an industrial implementation of the PCI bus. It uses a passive backplane and standardized Eurocard mechanics. The use of low-capacitance connectors allows up to eight PCI slots per backplane segment. CompactPCI defines additional signals beyond the basic PCI protocol. Among the features provided by these extra signals are: system slot identification, system enumeration and geographical addressing. Every board requires series termination of the bus signals. 165 C H A P T E R 10 Hot Plug and Hot Swap In high-availability, mission-critical environments, it is useful (in many cases absolutely essential) to be able to swap system components while the system is running. Attempting to do this in a system that has not taken Hot Pluggability into account will very likely result in component damage and system disruption. Two approaches to Hot Pluggability have been developed. The PCISIG invented Hot Plug for conventional PCI cards. PICMG created Hot Swap for CompactPCI. In some ways these approaches complement each other and in other ways they contrast. PCI Hot Plug Hot Plug is defined in the PCI Hot Plug Specification Rev. 1.0 dated October 1997. The primary objective of Hot Plug is “to enable higher availability of file and application servers by standardizing key aspects of the process of removing and installing PCI adapter cards while the system is running”. In an effort to expedite market acceptance of Hot Plug by making virtually any PCI card Hot Plug-gable, the specification puts the burden of hardware changes on the platform vendor. Specifically, the Hot Plug environment requires that each slot have: 166 Hot Plug and Hot Swap Power switches such that each board can be independently powered up and down. Bus isolation switches that electrically isolate the slot from the bus while a board is being inserted or removed. An independent RST# signal. A way of drawing an operator’s attention to a specific slot, an “attention indicator”, probably an LED. There may also be a slot state indicator to show whether the slot is on or off. The state indicator may be combined with the attention indicator. Ability to read the PRSNT[1:2]# signals while the board is isolated from the bus. Ability to read M66EN while the board is isolated from the bus. Hot Plug follows what may be termed a “no surprises” strategy. This means that before inserting or removing a board, the operator must inform the operating system of his intentions and wait until the system notifies him that it is OK to proceed. Hot Plug System Components Figure 10-1 shows the elements added to a system to support Hot Plug. These include: Hot Plug Controller. Provides hardware control of the power and bus isolation switches, individual RST#s and attention indicators. Monitors PRSNT[1:2]# and M66EN. Hot Plug System Driver. Software interface to the Hot Plug controller. Implements the Hot Plug primitives described below. 167 PCI Bus Demystified Operating System Hot-Plug Service User Management Agent Attention Indicator Bus and Power Switches Adapter Driver #1 …. Adapter Hot-Plug Driver #n Driver SW Layers HW Layers Platform Hot-Plug Controller Adapter Card #n Adapter Card #1 PCI Bus Figure 10-1: Hot Plug system components. Hot Plug Service Provides the interface to the user that allows the user to communicate insertion events to the system. Also interacts with adapter drivers to quiesce and activate the driver in response to insertion events. Hot Plug Insertion This is the sequence of events that occurs when a board is inserted into a Hot Plug environment. We start with the assumption that unoccupied slots are not powered, are isolated from the bus and that RST# is asserted. 1. The operator inserts the board in the slot. 2. The operator notifies the operating system that the board has been inserted in a specific slot 3. The Hot Plug Service notifies the Hot Plug System Driver to turn on the board. In turn, the Hot Plug System Driver directs the Hot Plug Controller to do the following: 168 ... - tailieumienphi.vn