MPC8280 datasheet(1019/1386 Pages) FREESCALE

1019 / 1386 page

ATM Controller and AAL0, AAL1, and AAL5

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

31-59

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.

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.

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

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

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. The cutoff decrease factor ranges from 1/64 (CDF=0b0110) to 1

(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.

Table 31-27. ABR-Specific TCTE Field Descriptions (continued)

Offset

Bits

Name

Description

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