Motorola MPC8260 User Manual

29-67

MOTOROLA

 

29.10.5.2.3  Free Buffer Pools
As Figure 29-44 shows, when a buffer pointer is fetched from a pool, the CP clears the
entryÕs valid bit and increments FBP#_PTR. After the CP uses an entry with the wrap bit
set (W = 1), it returns to the Þrst entry in the pool. After a buffer pointer is returned to the
pool, the user should set V to indicate that the entry is valid. If the CP tries to read an invalid
entry (V = 0), the buffer pool is out of free buffers; the global-buffer-pool-busy event is then
set in FCCE[GBPB] and a busy interrupt is sent to the interrupt queue specifying the ATM
channel code associated with the pool.

 

Figure 29-45 describes the structure of a free buffer pool entry.

Buffer 1 of FBP1

Buffer 2 of FBP1

Ch1 RxBD Table

0

BD 1

1

BD 2

1

BD 3

1

BD 4

1

BD 5

RBD_BASE

RBD_Offset

Buffer 3 of FBP1

Ch4 RxBD Table

1

BD 1

1

BD 2

1

BD 3

1

BD 4

RBD_BASE,
RBD_Offset 

Free Buffer Pool 1

FBP1_PTR

FBP1_BASE

Pointer 1

Pointer 2

Pointer 3

Pointer 4

Pointer 5

Pointer 6

Buffer 4

Buffer 5

Buffer 6

Notes: Buffers 2 and 3 are receiving data. After buffer 1 is processed, it can be returned to the pool.

V = 1

W = 0

Buffer Pointer

V = 1

W = 0

Buffer Pointer

V = 1

W = 0

Buffer Pointer

V = 0

W = 0

Invalid

V = 0

W = 0

Invalid

V = 0

W = 0

Invalid

V = 1

W = 0

Buffer Pointer

V = 1

W = 0

Buffer Pointer

V = 1

W = 1

Buffer Pointer

FBP#_BASE

Software (Core) Pointer

FBP#_PTR

Word