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CHAPTER 4 ATM CELL PROCESSOR
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Preliminary User’s Manual S14767EJ1V0UM00
4.5.1.1 Packet descriptor
A packet descriptor contains two words shown as Figure 4-10. Its address is word aligned.
Figure 4-10. Tx Packet Descriptor
-Tx packet descriptor
31
0
16 15
Attribute
CPCS-UU
CPI
8 7
16
MB
GFC
28
CLPM
27
PTI
26
24
23
19
IM
18
C10
17
AAL
20
Directory Address
31
0
31
1
30
ENC
29
Table. 4-1 is a list of Tx packet attributes. Detail will be given in Operation chapter.
Table 4-1. List of Tx Packet attribute
Field
Description
ENC
It contains Encapsulation bits to specify PPP Encapsulation modes.
CLPM
It contains CLP bit to be set in Tx cell header.
PTI
It contains PTI bit to be set in Tx cell header.
GFC
It contains GFC bit to be set in Tx cell header.
IM
It disables interruption and indication when Tx is completed.
C10
It enables generation and insertion of CRC10 code.
AAL
It specifies type of AAL.
MB
It indicates the number of mailbox.
CPCS-UU
It contains CPCS-UU bits to be set in Tx cell trailer.
CPI
It contains CPI bits to be set in Tx cell trailer.
4.5.1.2
Tx buffer directory
Tx buffer directory contains some buffer descriptors, not more than 255, and a link pointer. Its address is word
aligned. The end of buffer directory must be a link pointer. Buffer descriptors must be read and served from the top in
a sequential manner.
4.5.1.3 Tx buffer descriptor
Both a Tx buffer descriptor and a Tx link pointer consist of 2 words. DL bit, bit 30 of the first word, indicates that
these two words are a buffer descriptor (DL=1) or a link pointer (DL=0).
A Tx buffer descriptor is shown as Figure 4-11. Its address is word aligned. L bit, bit 31, indicates that the buffer
pointed by this descriptor contains the last potion of a packet.