Motorola MPC8260 - Manual (Page 848)

29-68 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part IV. Communications Processor Module
Table 29-32 describes free buffer pool entry Þelds.
29.10.5.2.4 Free Buffer Pool Parameter Tables
The free buffer pool parameters are held in parameter tables in the dual-port RAM; see
Table 29-33. 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.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Offset + 0x00 V Ñ W I Buffer Pointer (BP)
Offset + 0x02 Buffer Pointer (BP)
Figure 29-45. Free Buffer Pool Entry
Table 29-32. Free Buffer Pool Entry Field Descriptions
Offset Bits Name Description
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 Ñ 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.
4Ð15 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 parameter
FBP_ENTRY_EXT in the free buffer pool parameter table.
0x02 0Ð15
Table 29-33. Free Buffer Pool Parameter Table
Offset 1 Bits Name Description
0x00 Ñ FBP_BASE Free buffer pool base. Holds the pointer to the Þrst entry in the free buffer pool.
FBP_BASE should be word aligned. User-deÞned.
0x04 Ñ FBP_PTR Free buffer pool pointer. Pointer to the current entry in the free buffer pool.
Initialize to FBP_BASE.
0x08 Ñ FBP_ENTRY_EXT Free buffer pool entry extension. FBP_ENTRY_EXT[0Ð3] holds the four left bits
of FBP_ENTRY. FBP_ENTRY_EXT[4Ð15] should be cleared. User-deÞned.
0x0A 0 BUSY The CP sets this bit when it tries to fetch buffer pointer with V bit clear.
FCCE[GBPB] is also set. Initialize to zero.
1 RLI Red-line interrupt. Set by the CP when it fetches a buffer pointer with I = 1.
FCCE[GRLI] is also set. Initialize to zero.
2Р7 С Reserved, should be cleared.