Rm Cell Rate Representation - Motorola MPC8260 PowerQUICC II User Manual

Part IV. Communications Processor Module
Table 29-7. Fields and their Positions in RM Cells
Fields Octet Bits
Header 1Ð5 All
ID 6 All
DIR 7 0
BN 7 1
CI 7 2
NI 7 3
RA 7 4
Ñ 7 5-7
ER 8Ð9 All
CCR 10Ð11 All
MCR 12Ð13 All
QL 14Ð17 All
SN 18Ð21 All
Ñ 22Ð51 All
Ñ 52 0Ð5
CRC-10 52 6Ð7
53 All

29.5.2.1 RM Cell Rate Representation

Rates in the RM cells are represented in a binary ßoating-point format using a 5-bit
exponent (e), a 9-bit mantissa (m), and a 1-bit nonzero ßag (nz), as shown in Figure 29-15.
0 1 2
0 nz
The rate (in cells/second) is calculated as in Figure 29-16.
Initialize the trafÞc parameters (ER, MCR, PCR, or ICR) in the ABR protocol-speciÞc
connection tables using the rate formula in Figure 29-16.
29-26
ATM cell header
Protocol ID
Direction of RM cell (0 = forward, 1 = backward)
Backward notiÞcation (BN = 0, the cell was generated by the
source; BN=1, the cell was generated by the network or by the
destination)
Congestion indication. (1 = congestion, 0 = otherwise)
No increase indication. (1 = no increase allowed, 0 = otherwise)
Not used (ATM Forum ABR)
Reserved, should be cleared.
Explicit rate; see Section 29.5.2.1
Current cell rate; see Section 29.5.2.1
Min cell rate; see Section 29.5.2.1
Not used (ATM Forum ABR)
Not used (ATM Forum ABR)
Reserved, should be cleared.
Reserved, should be cleared.
CRC-10
3 4 5 6 7
Exponent
Figure 29-15. Rate Format for RM Cells
e
Rate = 2
Figure 29-16. Rate Formula for RM Cells
MPC8260 PowerQUICC II UserÕs Manual
Description
8 9 10 11
Mantissa
æ ö
m
´ ´
1 + -------- - nz
è ø
512
Value
RM-VCC
PTI=6
1
0
0
0
0
0x6A for each byte
0
12 13 14 15
MOTOROLA