MPC8280 datasheet(1028/1386 Pages) FREESCALE

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ATM Controller and AAL0, AAL1, and AAL5

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

31-68

Freescale Semiconductor

Table 31-32 describes free buffer pool entry fields.

31.10.5.2.4

Free Buffer Pool Parameter Tables

The free buffer pool parameters are held in parameter tables in the dual-port RAM; see Table 31-33.

FBT_BASE in the parameter RAM points to the base address of these tables. Each of the four free buffer

pools has its own parameter table with a starting address given by FBT_BASE+ RCT[BPOOL]

× 16.

234

Offset + 0x00

—

Buffer Pointer (BP)

Offset + 0x02

Buffer Pointer (BP)

Figure 31-45. Free Buffer Pool Entry

Table 31-32. Free Buffer Pool Entry Field Descriptions

Offset

Bits

Name

Description

0x00

Valid buffer entry.

0 This free buffer pool entry contains an invalid buffer pointer.

1 This free buffer pool entry contains a valid buffer pointer.

—

Reserved, should be cleared.

Wrap bit. When set, this bit indicates the last entry in the circular table. During initialization,

the host must clear all W bits in the table except the last one, which must be set.

Red-line interrupt. Can be used to indicate that the free buffer pool has reached a red line

and additional buffers should be added to this pool to avoid a busy condition.

0 No interrupt is generated.

1 A red-line interrupt is generated when this buffer is fetched from the free buffer pool.

4–15

Buffer pointer. Points to the start address of the receive buffer. The four msbs are control

bits, and the four msbs of the real buffer pointer are taken from the four msbs of the

parameter FBP_ENTRY_EXT in the free buffer pool parameter table.

0x02

0–15

Table 31-33. Free Buffer Pool Parameter Table

Offset 1

Bits

Name

Description

0x00

—

FBP_BASE

Free buffer pool base. Holds the pointer to the first entry in the free buffer pool.

FBP_BASE should be word aligned. User-defined.

0x04

—

FBP_PTR

Free buffer pool pointer. Pointer to the current entry in the free buffer pool.

Initialize to FBP_BASE.

0x08

—

FBP_ENTRY_EXT Free buffer pool entry extension. FBP_ENTRY_EXT[0–3] holds the four left bits

of FBP_ENTRY. FBP_ENTRY_EXT[4–15] should be cleared. User-defined.

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