Buffer Descriptors and Connection Tables
MPC885 PowerQUICC Family Reference Manual, Rev. 2
37-10
Freescale Semiconductor
37.2
Receive and Transmit Connection Tables (RCTs and TCTs)
The receive and transmit connection tables (RCTs and TCTs) hold configuration and control information
and temporary parameters for each receive and transmit ATM channel. Although the transmit and receive
sections of the same channel number are independent of each other, their RCTs and TCTs are paired
together in connection tables (CTs). Each CT is 64 bytes. The upper 32 bytes is used for the RCT, and the
lower 32 bytes is the TCT.
Note that because their formats change, the CTs are renamed PTP RCT and PTP TCT for receive and
transmit channel numbers used in port-to-port switching.
The CTs for internal channels (channels 0–31) are in the dual-port RAM. In extended channel mode
(UTOPIA only), the tables for external channels (numbered 32 and above) are kept in external memory.
The structure of the CTs is shown in
Figure 37-7
.
0x08
—
CPCS-UU and
CPI/HEADER_L
CPCS-UU and CPI (AAL5 only and RH = 0 and L = 1). Valid only when the
current BD is the last BD of an AAL5 frame. CPCS-UU and CPI are used in the
frame trailer to transfer user-to-user (UU) information and common part
indications (CPI). The transmitter copies this field to the AAL5 frame trailer.
HEADER_L—Lower order half word of the replacement header (AAL5 only and
RH = 1). HEADER_L and HEADER_H comprise the new cell header to be
stored in the TCT CHEAD field. See the TxBD[RH] description above.
The byte ordering of the 4-byte HEADER field is little endian; that is, the MSB is
at location 0x0B, and the LSB is at location 0x08.
0x0A
—
HEADER_H
Higher order half word of the replacement header (AAL5 only and RH = 1).
Applies only when the RH bit is set; it is reserved otherwise. See the
HEADER_L description above.
0x0C
—
Cell header
expansion 1, 2,
and 3
Cell header expansion 1, 2, and 3 (UTOPIA expanded cell mode only). These
fields are added to the BD when expanded cells are enabled (SRSTATE[EC] is
set in the UTOPIA parameter RAM). The size of the cell header expansion is
programmable and is determined by ECSIZE in the UTOPIA parameter RAM.
For AAL5 channels, the ATM controller copies the contents of the cell header
expansion fields from the first BD of the current frame and appends them to
every cell of the frame sent. For AAL0 channels, these fields are copied into the
expanded cell header of the cell.
Cell header expansion 1 is the first word to be sent; cell header expansion 3 is
the last. The bytes are ordered according to the DMA byte ordering
(programmed through STFCR in the parameter RAM).
Table 37-2. ATM TxBD Field Descriptions (continued)
Offset from
TBD_PTR
Bits
Name
Description
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