Motorola PowerQUICC II MPC8280 Series Reference Manual page 1078

ATM Memory Structure
Table 31-27. ABR-Specific TCTE Field Descriptions (continued)
Offset Bits Name
3 NI-TA No increase–turn-around cell. Holds the NI of the last received F-RM cell. If another F-RM
cell arrives before the previous one was turned around, NI-TA is overwritten by the new RM
cell's NI.
4–6 — Reserved, should be cleared.
7 CP-TA Cell loss priority–turn-around cell. Holds the CLP of the last received F-RM cell. If another
F-RM cell arrives before the previous one was turned around, CP-TA is overwritten by the
new RM cell's CLP.
8–9 — Reserved, should be cleared.
10 CI-VC Congestion indication -VC. Holds the EFCI (explicit forward congestion indication) of the
last user data cell. The CI bit of the turned around RM cell is ORed with the CI-VC. Should
be cleared initially.
11–15 — Reserved, should be cleared.
0x08 — MCR Minimum cell rate Holds the minimum number of cells/sec of the current ABR channel.
Uses the ATMF TM 4.0 floating-point format.
0x0A — UNACK Used by the CP to count F-RM cells sent in an absence of received B-RM cells. Should be
cleared initially.
0x0C — ACR Allowed cell rate The cells per second allowed for the current ABR channel. Uses the ATMF
TM 4.0 floating-point format. Initialize with ICR.
0x0E 0 ACRC ACR change. Indicates a change in ACR. Initialize to one.
1–15 — Reserved, should be cleared.
0x10 — RCTS RM cell time stamp. Used exclusively by the CP. Initialize to zero.
0x14 0 FRST First turn. Used exclusively by the CP. Indicates the first turn of a backward RM cell, which
has priority over a data cell. Initialized to 0.
1–3 — Reserved, should be cleared.
4–7 CDF Cutoff decrease factor. Controls the decrease in the ACR associated with missing B-RM
cells feedback. CDF represents a negative exponent of two, that is, the cutoff decrease
factor = 2
(CDF=0b0000). All other CDF values falling outside this range are invalid.
8–15 COUNT Count. Used only by the CP. Holds the number of cells sent since the last forward RM cell.
Initialize with Nrm (in the parameter RAM).
0x16 — ICR Initial cell rate. The number of cells per second of the current ABR channel. The channel's
ACR is initialized with ICR. ICR uses the ATMF TM 4.0 floating-point format.
0x18 — CRM Missing RM cells count. Limits the number of forward RM cells that may be sent in the
absence of received backward RM cell. The CRM is in units of cells.
0x1A — ADTF ADTF–ACR decrease time factor. The ADTF period is 500 ms as defined in the TM 4.0.
The ADTF value is defined by the system clock and the time stamp timer prescaler; see
Section 14.3.8, "RISC Time-Stamp Control Register (RTSCR)." For a time stamp prescaler
of 1 µs, ADTF should be programmed to 500m/(1µs × 1024)= 488.
31-64
Freescale Semiconductor, Inc.
-CDF
. The cutoff decrease factor ranges from 1/64 (CDF=0b0110) to 1
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