Freescale Semiconductor MPC8260 - Manual (Page 978)

ATM Controller and AAL0, AAL1, and AAL5
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
30-58 Freescale Semiconductor
Table 30-25 describes VBR protocol-specific TCTE fields.
30.10.2.3.7 UBR+ Protocol-Specific TCTE
Figure 30-35 shows the UBR+ protocol-specific TCTE.
0 1 7 8 15
Offset + 0x00 SCR
Offset + 0x02 Burst Tolerance (BT)
Offset + 0x04 Out of Buffer Rate (OOBR)
Offset + 0x06 Sustain Rate Remainder (SRR) SCR Fraction (SCRF)
Offset + 0x08 Sustain Rate (SR)
Offset + 0x0A
Offset + 0x0C VBR2 —
Offset + 0x0E-1E —
Figure 30-34. Transmit Connection Table Extension (TCTE)—VBR Protocol-Specific
Table 30-25. VBR-Specific TCTE Field Descriptions
Offset Bits Name Description
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
state.
1 VBR Type 2. CLP=0 cells are rescheduled by PCR or SCR according to the GCRA state.
CLP=1 cells are rescheduled by PCR.
1–15 — Reserved, should be cleared.
0x0E–
0x1E
— — Reserved, should be cleared.