Motorola PowerQUICC II MPC8280 Series Reference Manual page 1087

Figure 31-45 describes the structure of a free buffer pool entry.
0 1
Offset + 0x00 V —
Offset + 0x02
Table 31-32 describes free buffer pool entry fields.
Table 31-32. Free Buffer Pool Entry Field Descriptions
Offset Bits Name
0x00 0 V 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.
1 — Reserved, should be cleared.
2 W 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.
3 I 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 BP 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
0x02 0–15
parameter FBP_ENTRY_EXT in the free buffer pool parameter table.
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.
Table 31-33. Free Buffer Pool Parameter Table
1
Offset Bits Name
0x00 — FBP_BASE
0x04 — FBP_PTR
0x08 — FBP_ENTRY_EXT Free buffer pool entry extension. FBP_ENTRY_EXT[0–3] holds the four left bits
MOTOROLA Chapter 31. ATM Controller and AAL0, AAL1, and AAL5
Freescale Semiconductor, Inc.
2 3 4
W I
Buffer Pointer (BP)
Figure 31-45. Free Buffer Pool Entry
Free buffer pool base. Holds the pointer to the first entry in the free buffer pool.
FBP_BASE should be word aligned. User-defined.
Free buffer pool pointer. Pointer to the current entry in the free buffer pool.
Initialize to FBP_BASE.
of FBP_ENTRY. FBP_ENTRY_EXT[4–15] should be cleared. User-defined.
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ATM Memory Structure
Buffer Pointer (BP)
Description
Description
15
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