Motorola MPC8260 - Manual (Page 839)

29-59 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part IV. Communications Processor Module
4Р6 С Reserved, should be cleared.
7 CP-TA Cell loss priorityÐturn-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 cellÕs CLP.
8Р9 С 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.
Initialize to 0.
11Р15 С Reserved, should be cleared.
0x08 Ñ MCR Minimum cell rate Holds the minimum number of cells/sec of the current ABR channel.
Uses the ATMF TM 4.0 ßoating-point format.
0x0A Ñ UNACK Used by the CP to count F-RM cells sent in an absence of received B-RM cells. Initialize to
0.
0x0C Ñ ACR Allowed cell rate The cells per second allowed for the current ABR channel. Uses the
ATMF TM 4.0 ßoating-point format. Initialize with ICR.
0x0E 0 ACRC ACR change. Indicates a change in ACR. Initialize to one.
1Р15 С Reserved, should be cleared.
0x10 Ñ 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 Þrst turn of a backward RM cell, which
has priority over a data cell. Initialized to 0.
1Р3 С Reserved, should be cleared.
4Ð7 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 . The cutoff decrease factor ranges from 1/64 (CDF=0b0110) to 1
(CDF=0b0000). All other CDF values falling outside this range are invalid.
8Ð15 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 Ñ ICR Initial cell rate. The number of cells per second of the current ABR channel. The channelÕs
ACR is initialized with ICR. ICR uses the ATMF TM 4.0 ßoating-point format.
0x18 Ñ 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 Ñ ADTF ADTFÐACR decrease time factor. The ADTF period is 500 ms as deÞned in the TM 4.0.
The ADTF value is deÞned by the system clock and the time stamp timer prescaler; see
Section 13.3.7, ÒRISC Time-Stamp Control Register (RTSCR).Ó For a time stamp prescaler
of 1 µs, ADTF should be programmed to 500m/(1µs
´ 1024)= 488.
0x1C Ñ ER Explicit rate. Holds the explicit rate value (in cells/sec) of the current ABR channel. ER is
copied to the F-RM cell ER Þeld. The user usually initializes this Þeld to PCR. ER uses the
ATMF TM 4.0 ßoating-point format.
0x1E Ñ ER-BRM Explicit rate-backward RM cell. Holds the maximum explicit rate value (in cells/sec)
allowed for B-RM cells. The ER-TA Þeld which is inserted to each B-RM cell is limited by
this value. ER-BRM uses the ATMF TM 4.0 ßoating-point format.
Table 29-27. ABR-Specific TCTE Field Descriptions (Continued)
Offset Bits Name Description