XIO2000 datasheet(37/150 Pages) TI

37 / 150 page

Feature/Protocol Descriptions

November 2005

SCPS097B

To enable the 128-phase, WRR time-based arbiter, two configuration registers must be written. Bit 1

(PORTARB_LEVEL_1_EN) in the upstream isochrony control register at offset 04h (see Section 6.4) within

the device control memory window register map must be asserted. The VC1 resource control register at offset

170h within the PCI Express VC extended configuration space has a PORT_ARB_SELECT field that must

be set to 100b (see Section 5.22).

Table 3−7 identifies and describes the registers associated with 128-phase, WWR time-based arbitration

mode.

Table 3−7. 128-Phase, WRR Time-Based Arbiter Registers

DESCRIPTION

PCI Express VC extended

configuration registers

1C0h to 1FCh

Port arbitration table

(see Section 5.28)

16-doubleword sized configuration registers that are the registered version of the

128-phase, WRR port arbitration table. Each port arbitration table entry is a 4-bit

field.

PCI Express VC extended

configuration register 170h

VC1 resource control

(see Section 5.25)

Bits 19:17 (PORT_ARB_SELECT) equal to 100b define the port arbitration

mechanism as 128-phase WRR.

Bit 16 (LOAD_PORT_TABLE), when written with a 1b, transfers the port arbitration

table configuration register values to the internal registers used by the PCI bus

arbiter.

PCI Express VC extended

configuration register 176h

VC1 resource status

(see Section 5.26)

Bit 0 (PORT_TABLE_STATUS) equal to 1b indicates that the port arbitration table

configuration registers were updated but not loaded into the internal arbitration

table.

Device control memory

window register 04h

Upstream isochrony

control (see Section 6.4)

Bit 1 (PORTARB_LEVEL_1_EN) must be asserted to enable the 128-phase, WRR

time-based arbiter.

3.5.1.3

128-Phase, WRR Aggressive Time-Based Arbiter

The last option for PCI port arbitration is 128-phase, WRR aggressive time-based arbitration mode. This

arbitration mode performs the same as isochronous mode arbitration, but with one difference. When an

isochronous timing event occurs, the PCI bus arbiter deliberately stops a secondary bus master in the middle

of the transaction to assure that isochrony is preserved. The register setup for this arbitration option is the

same as the 128-phase, WRR time-based arbiter option with the following addition. Bit 2

(PORTARB_LEVEL_2_EN) in the device control memory window upstream isochrony control register at offset

04h must be asserted (see Section 6.4).

3.5.2 PCI Isochronous Windows

The bridge has four separate windows that allow PCI bus-initiated memory transactions to be labeled with a

PCI Express traffic class (TC) beyond the default TC0. Each window designates a range of PCI memory space

that is mapped to a specified TC label. This advance feature is configured through the device control memory

window register map.

Table 3−8 identifies and describes the registers associated with isochronous arbitration mode.

Table 3−8. PCI Isochronous Windows

DESCRIPTION

Device control memory

window register 08h

Upstream isochronous window 0

control (see Section 6.5)

Bits 3:1 (ISOC_WINDOW_EN) indicate that memory addresses within the

base and limit addresses are mapped to a specific traffic class ID.

Bit 0 (TC_ID) identifies the specific traffic class ID.

Note: Memory-mapped register space exists for four upstream windows.

Only window 0 is included in this table.

Device control memory

window register 0Ch

Upstream isochronous window 0

base address (see Section 6.6)

Window 0 base address

Device control memory

window register 10h

Upstream isochronous window 0

limit address (see Section 6.7)

Window 0 limit address

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