MPC8280 datasheet(383/1386 Pages) FREESCALE

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PCI Bridge

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

9-75

9.12.3.3

Outbound FIFOs

The outbound queues are used to send messages from the local processor to a remote host processor. I2O

defines two outbound FIFOs—an outbound post FIFO and an outbound free FIFO.

The following registers should be accessed only from the 60x bus and only in agent mode. Accesses while

in host mode or from the PCI bus have undefined results.

9.12.3.3.1

Outbound Free_FIFO Head Pointer Register (OFHPR) and

Outbound Free_FIFO Tail Pointer Register (OFTPR)

The outbound free list FIFO holds the MFAs of the empty outbound message locations in local memory.

When the local processor is ready to send an outbound message, it first fetches an empty MFA by reading

the OFTPR. It then writes the message into the MFA. The OFTPR is managed by the local processor.

When an external PCI master has completed use of a message that was posted in the outbound post FIFO

and wants to return the MFA to the free list, it writes to OFQPR (refer to Section 9.12.3.4.2, “Outbound

FIFO Queue Port Register (OFQPR)”). The PCI bridge’s I2O unit then writes the MFA to the OFHPR.

This, in turn, causes the outbound free head pointer to be advanced.

Free MFAs are returned by the PCI masters to the outbound free list FIFO that is pointed to by the

outbound free_FIFO head pointer register, described in Figure 9-69 and Table 9-54. The PCI write

references the outbound queue port. The I2O hardware automatically advances the address, (i.e. OFHPR)

after every write.

Figure 9-69. Outbound Free_FIFO Head Pointer Register (OFHPR)

Table 9-53. IPTPR Field Descriptions

Bits

Name

Description

31–20

QBA

Queue base address. When read returns the contents of QBAR bits 31-20.

19–2

IPTP

Inbound post_FIFO tail pointer. Local memory offset of the tail pointer of the inbound post list

FIFO.

1–0

—

Reserved, should be cleared.

Field

QBA

OFHP

Reset

0000_0000_0000_0000

R/W

Addr

0x104C2

Field

OFHP

—

Reset

0000_0000_0000_0000

R/W

Addr

0x104C0

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