Motorola MPC8260 User Manual

29-32

MOTOROLA

BRC reception uses the regular AAL0 raw cell queue. On receiving two consecutive BRC
cells, the management layer can calculate the following:

¥

The difference between two TUCs (Nt)

¥

The difference between two TRCCs (Nr)

Information about the connection can be gained by comparing Nt and Nr:

¥

If Nt > Nr, the difference indicates the number of lost cells of this block test.

¥

If Nt < Nr, the difference indicates the number of misinserted cells of this block test.

¥

When Nt = Nr, no cells are lost or misinserted.

Typical ATM cells are 53 bytes long and consist of a 4-byte header, 1-byte HEC, and 48-
byte payload. The MPC8260 also supports user-deÞned cells with up to 12 bytes of extra
header Þelds for internal information for switching applications. This choice is made during
initialization by writing to the FPSMR; see Section 29.13.2, ÒFCC Protocol-SpeciÞc Mode
Register (FPSMR).Ó As shown in Figure 29-19, the extra header size can vary between 1 to
12 bytes (byte resolution) and the HEC octet is optional. 

FMC Cell

Data Cell

Data Cell

FMC Cell

Data Cell

Data Cell

FMC Cell

512 User Cells

512 User Cells

TUC0

Source Cells

Stream

1

2

3

TSTP

BEDC

TUC0+1

TUC0

TSTP

BEDC

TUC0+1

TUC0

TSTP

BEDC

TUC0+1

BRC Cell

TUC0

Destination BRCÕs

Transmit Stream

1

TUC0+1

TSTP

BLER

TRCC0

TRCC0+1

BRC Cell

TUC0

2

TUC0+1

TSTP

BLER

TRCC0

TRCC0+1

BRC Cell

TUC0

3

TUC0+1

TSTP

BLER

TRCC0

TRCC0+1