Motorola PowerQUICC II MPC8280 Series Reference Manual page 1075

31.10.2.3.6 VBR Protocol-Specific TCTE
Figure 31-34 shows the VBR protocol-specific TCTE.
0
Offset + 0x00
Offset + 0x02
Offset + 0x04
Offset + 0x06
Offset + 0x08
Offset + 0x0A
Offset + 0x0C VBR2
Offset + 0x0E-1E
Figure 31-34. Transmit Connection Table Extension (TCTE)—VBR Protocol-Specific
Table 31-25 describes VBR protocol-specific TCTE fields.
Table 31-25. VBR-Specific TCTE Field Descriptions
Offset Bits Name
0x00 — SCR Sustain cell rate. Holds the sustain cell rate (in slots) permitted for this channel according
to the traffic contract. To pace the channel's sustain cell rate, the APC performs a
continuous-state leaky bucket algorithm (GCRA).
0x02 — BT Burst tolerance. Holds the burst tolerance permitted for this channel according to the traffic
contract. The relationship between the BT and the maximum burst size (MBS) is
BT=(MBS-2) × (SCR-PCR) + SCR.
0x04 — OOBR Out-of-buffer rate. In out of buffer state (when the transmitter tries to open TxBD whose R
bit is not set) the APC reschedules the current channel according to OOBR rate.
0x06 0–7 SRR Sustain rate remainder. Holds the sustain rate remainder after adding the pace fraction field
to the additive channel sustain rate. Used by the APC to calculate the channel GCRA (leaky
bucket) state. Initialized to 0.
8–15 SCRF Holds the sustain cell rate fraction of this channel in units of 1/256 slot.
0x08 — SR Sustain rate. Used by the APC to hold the sustain rate after adding the pace field to the
additive channel sustain rate. Used by the APC to calculate the channel GCRA (leaky
bucket) state.
0x0C 0 VBR2 VBR type
0 Regular VBR. CLP=0+1 cells are rescheduled by PCR or SCR according to the GCRA
1 VBR Type 2. CLP=0 cells are rescheduled by PCR or SCR according to the GCRA state.
1–15 — Reserved, should be cleared.
0x0E– — — Reserved, should be cleared.
0x1E
MOTOROLA Chapter 31. ATM Controller and AAL0, AAL1, and AAL5
Freescale Semiconductor, Inc.
1
Out of Buffer Rate (OOBR)
Sustain Rate Remainder (SRR)
state.
CLP=1 cells are rescheduled by PCR.
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7 8
SCR
Burst Tolerance (BT)
SCR Fraction (SCRF)
Sustain Rate (SR)
—
—
Description
ATM Memory Structure
15
31-61