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CHAPTER 5 SAR FUNCTION
136
<9>
CPCS-UU, CPI
The
μ
PD98405 inserts the patterns set by the user in these fields, into the CPCS-UU and CPI fields
of the AAL-5 trailer. These fields are valid only when a packet of AAL-5 type is transmitted (when
AAL bit = 1); otherwise, the
μ
PD98405 ignores these fields.
CPCS-UU: CPCS user-user indication
CPI:
Common part indication
<10> SIZE
Single-buffer mode:
Stores the size of the buffer, in bytes.
Multi-buffer mode:
This field is meaningless and is ignored by the
μ
PD98405.
<11> ADDRESS
Single-buffer mode
Stores the data buffer start address. Data buffers can be allocated
starting from a byte boundary in system memory. This field,
therefore, stores a 32-bit byte address.
Multi-buffer mode
Stores the start address of the first buffer descriptor in the packet
directory. Buffer descriptors must be allocated starting from word
boundaries in system memory. The low-order two bits of the address
stored in this field must, therefore, be 00.
Link pointer (D/P = 0)
Stores the start address of the first packet descriptor in the next
transmit queue. Packet descriptors must be allocated starting from
word boundaries in system memory. The low-order two bits of the
address stored in this field must, therefore, be 00.
(2) Packet directory
The packet directory is set when a transmit packet is configured in multi-buffer mode. It need not be set in
single-buffer mode. The packet directory consists of contiguous 2-word buffer descriptors, as shown in
Figure 5-15. The buffer descriptor is a pointer to the first address of the data buffer.
Figure 5-15. Format of Buffer Descriptor
0
16 15
0
31
0
ADDRESS
SIZE
30
31
LAST