Buffer Descriptors and Connection Tables
MPC885 PowerQUICC Family Reference Manual, Rev. 2
37-22
Freescale Semiconductor
0x32
0–4
—
Reserved
5–10
TPMT
Transmit performance monitoring table number. The address of the table in the
dual-port RAM is PMPTR+(32xTPMT). See
Section 39.3.4, “Performance
Monitoring Tables
.”
Note that for OAM F4, more than one TCT[TPMT} could point to the same PM table.
14
AVCF
Auto VC off. When the last buffer associated with this VC has been sent and no more
buffers are ready in the VC’s TxBD table, the transmitter can automatically
deactivate the channel by removing it from the APC scheduling table. If this channel
is used for port-to-port switching, see the PTP RCT[AVCO] description in.
0 Auto-VC-off disabled. The APC continues to schedule this channel.
1 Auto-VC-off enabled. To continue transmission after the host prepares buffers,
issue a
TRANSMIT
ACTIVATE
CHANNEL
command.Note that for channels subject to
frequent underruns, such as UBR channels, set AVCF for improved performance
by freeing the transmitter from polling the BD table each time the channel is
scheduled.
15
ACT
Active status. Indicates the current status of the channel.
0 Not active. Cleared after the channel is removed from the APC scheduling table
when the host issues a
TRANSMIT
DEACTIVATE
CHANNEL
command or when the CP
is programmed to automatically deactivate the channel when buffers are not
ready (TCT[AVCF] = 1). Note that ACT is not cleared until the next time the
channel is encountered in the APC scheduling table (maximum latency of one full
pass through the APC scheduling table).
1 Active. Set by the CP when the host issues a
TRANSMIT
ACTIVATE
CHANNEL
command. Also, for PTP, the CP activates the channel when the associated
receive channel is auto-VC-on enabled and the transmit channel is auto-VC-off
enabled (PTP RCT[AVCO]=1 and TCT[AVCF]=1).
0x34
—
CHEAD
Channel header (AAL5 only). Contains the full (4-byte) cell header for this AAL5
channel. The transmitter appends CHEAD and the calculated HEC to the payload
to create a complete cell. This field should be initialized by the user and should not
be modified while the channel is active.
Note that the byte ordering of this field is reversed; that is, CHEAD[0–7] is the LSB
with CHEAD[0] the msb, and CHEAD[24–31] is the MSB with CHEAD[24] the msb.
0x38
—
APCL
APC link. Used by the CP to link additional channels to the same APC time slot
occupied by the current channel. Initialize this field with 0xFFFF to indicate the end
of the linked list.
0x3A
—
APCPR
APC pace remainder. Contains the remainder of the rate generated by the APC after
adding the pace FRACTION to the cumulative APCPR.
Should be cleared during initialization.
Table 37-5. TCT Field Descriptions (continued)
CT Offset
Bits
Name
Description
Содержание PowerQUICC MPC870
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