DS495 Datasheet, PDF(10/12 Page) Xilinx, Inc

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DS495 Datasheet, PDF (10/12 Pages) Xilinx, Inc – PCI Arbiter

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PCI Arbiter (v1.00a)

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pci_clk

pci_rst_n

pci_req_n(0)

pci_req_n(1)

pci_req_n(2)

pci_req_n(3)

pci_req_n(4)

pci_req_n(5)

pci_frame

pci_irdy_n

pci_gnt_n(0)

pci_gnt_n(1)

pci_gnt_n(2)

pci_gnt_n(3)

pci_gnt_n(4)

pci_gnt_n(5)

X495_10_101306

Figure 10: PCI_Arbiter Grant to a Second Master After First Fails to Respond and Goes Away

Figure 11 shows the situation of a master agent, number zero, requesting and gaining access, then

going away. During the bus transaction for master agent zero, a second master, number one, requests

access. The PCI Arbiter detects this as a multiple request situation even though the first request

expired. The PCI Arbiter responds by deasserting grant zero forcing the master agent zeroâs latency

timer to activate and eventually terminate the bus transaction for master zero. Following this, the PCI

Arbiter grants access to master agent one which then proceeds with its own transaction. In this case

master one is the last active master and becomes the parking agent of choice for the PCI Arbiter.

Figure Top x-ref 11