In the hierarchical cluster connection model an

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Unformatted text preview: tion format register (DFR) defines the interpretation of the logical destination information (refer to Figure 7-7). The DFR register can be programmed for flat model or cluster model interrupt delivery modes. 31 28 0 Model Address: 0FEE0 00E0H Value after reset: FFFF FFFFH Reserved (All 1s) Figure 7-7. Destination Format Register (DFR) FLAT MODEL For the flat model, bits 28 through 31 of the DFR must be programmed to 1111. The MDA is interpreted as a decoded address. This scheme allows the specification of arbitrary groups of local APICs simply by setting each APIC’s bit to 1 in the corresponding LDR. In the flat model, up to 8 local APICs can coexist in the system. Broadcast to all APICs is achieved by setting all 8 bits of the MDA to ones. CLUSTER MODEL For the cluster model, the DFR bits 28 through 31 should be programmed to 0000. In this model, there are two basic connection schemes: flat cluster and hierarchical cluster. In the flat cluster connection model, all clusters are assumed to be connected on a single APIC bus. Bits 28 through 31 of the MDA contains the encoded address of the destination cluster. These bits are compared with bits 28 through 31 of the LDR to determine if the local APIC is part of the cluster. Bits 24 through 27 of the MDA are compared with Bits 24 through 27 of the LDR to identify individual local APIC unit within the cluster. Arbitrary sets of processors within a cluster can be specified by writing the target cluster address in bits 28 through 31 of the MDA and setting selected bits in bits 24 through 27 of the MDA, corresponding to the chosen members of the cluster. In this mode, 15 clusters (with cluster addresses of 0 through 14) each having 4 processors can be specified in the message. The APIC arbitration ID, however, supports only 15 agents, and hence the total number of processors supported in this mode is limited to 15. 7-21 MULTIPLE-PROCESSOR MANAGEMENT Broadcast to all local APICs is achieved by setting all destination bits to one. This guarantees a match on all clusters, and selects all APICs in each cluster. In the hierarchical cluster connection model, an arbitrary hierarchical network can be created by connecting different flat clusters via independent APIC buses. This scheme requires a cluster manager within each cluster, responsible for handling message passing between APIC buses. One cluster contains up to 4 agents. Thus 15 cluster managers, each with 4 agents, can form a network of up to 60 APIC agents. Note that hierarchical APIC networks requires a special cluster manager device, which is not part of the local or the I/O APIC units. ARBITRATION PRIORITY Each local APIC is given an arbitration priority of from 0 to 15 upon reset. The I/O APIC uses this priority during arbitration rounds to determine which local APIC should be allowed to transmit a message on the APIC bus when multiple local APICs are issuing messages. The local APIC with the highest arbitration priority wins access to the APIC bus. Upon completion of an arbitration round, the winning local APIC lowers its arbitration priority to 0 and the losing local APICs each raise theirs by 1. In this manner, the I/O APIC distributes message bus-cycles among the contesting local APICs. The current arbitration priority for a local APIC is stored in a 4-bit, software-transparent arbitration ID (Arb ID) register. During reset, this register is initialized to the APIC ID number (stored in the local APIC ID register). The INIT-deassert command resynchronizes the arbitration priorities of the local APICs by resetting Arb ID register of each agent to its current APIC ID value. 7.5.10. Interrupt Distribution Mechanisms The APIC supports two mechanisms for selecting the destination processor for an interrupt: static and dynamic. Static distribution is used to access a specific processor in the network. Using this mechanism, the interrupt is unconditionally delivered to all local APICs that match the destination information supplied with the interrupt. The following delivery modes fall into the static distribution category: fixed, SMI, NMI, EXTINT, and start-up. Dynamic distribution assigns incoming interrupts to the lowest priority processor, which is generally the least busy processor. It can be programmed in the LVT for local interrupt delivery or the ICR for bus messages. Using dynamic distribution, only the “lowest priority” delivery mode is allowed. From all processors listed in the destination, the processor selected is the one whose current arbitration priority is the lowest. The latter is specified in the arbitration priority register (APR), refer to Section, “Arbitration Priority Register (APR)” If more than one processor shares the lowest priority, the processor with the highest arbitration priority (the unique value in the Arb ID register) is selected. In lowest priority mode, if a focus processor exists, it may accept the interrupt, regardless of its priority. A processor is said to be...
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