Buffer Descriptors and Connection Tables
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
37-27
37.2.3
Transmit Connection Table Extensions (TCTE)
Extensions to the TCTs called TCTE are used to hold additional parameters for traffic shaping, primarily
for VBR channels (or for future development). They also hold the optional out-of-buffers rate parameter
(OOBR) for UBR channels. The TCTE structure is modeled on the connection tables. Each TCTE is 32
bytes.
For internal channels, the TCTEs are located in the dual-port RAM at the base address TCTEBASE
(programmed in the parameter RAM). In extended channel mode, parameters for external channels are
kept in external memory at the base address ETCTEBASE (also programmed in the parameter RAM).
Example TCTEs for internal and external VBR/UBR channels are shown in
Figure 37-12
. Note that in
extended channel mode, an additional internal TCTE is reserved for CP use in the memory space
immediately above the TCTEBASE pointer.
0x3C
0
OUT
APC out. Can be used as a completion flag for the
TRANSMIT
DEACTIVATE
CHANNEL
command. When the
TRANSMIT
DEACTIVATE
CHANNEL
command is
issued, OUT is immediately set. OUT is then cleared when the channel is
actually removed from the APC scheduling table (TCT[ACT] is cleared).
0 No
TRANSMIT
DEACTIVATE
CHANNEL
command is pending.
1 The channel is waiting to be removed from the APC scheduling table.
1
BNR
Buffer not ready. Reserved for internal use, should be cleared during
initialization.
2–3
TSERVICE
Traffic service. Selects the type of ATM service and the associated traffic
parameters.
00 CBR and UBR (maintain PCR)
01 Reserved
10 VBR (maintain PCR, SCR, BT, and OOBR)
11 UBR (maintain PCR and OOBR)
4–15
APCP
APC pace. Contains the channel’s APC pacing. When the channel is placed
in the transmit queue, the APC reschedules the channel in a new position
(time slot) in the APC scheduling table. The new slot position is (the current
slot po APCP) modulo the table length. Note that the APCP value
selected is bounded as shown below:
and:
For more information about the APC, see
Chapter 40, “ATM Pace Control.”
0x3E
—
APCPF
APC pace fraction. Contains the channel’s APCP_FRACTION in units of
1/65536 of a time slot. For example, a pace of 1.5 is obtained by programming
APCP to 1 and APCPF to 0x8000. The pace thus becomes 1+32768/65536,
or a value of 1.5.
Table 37-6. PTP TCT Field Descriptions (continued)
CT Offset
Bits
Name
Description
1
APCP
APCPF
65536
---------------------
+
⎝
⎠
⎛
⎞
APCTablelength
1
–
[
]
≤
≤
APCP
4094
≤
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