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II
2.1.5 Token Rotation Time at Start of Access Classes
Token rotation time at the start of each access class is measured in octet times from the station's
receipt of the token to the TBC's entrance into that access class. There is one token rotation timer
for each of the lower three access classes and one for ring maintenance. These statistics along
with the target rotation time for each access class are used by the TBC to implement the priority
mechanism. These statistics have no meaning if the priority access class is disabled or if the
station is not a member of the logical ring. These statistics can be accessed by the host via the
READ VALUE command.
Offset
o
C
B
A
o
~C,
10, 14
Token Rotation Time at Start of Access Class IPrescaled)
2.1.6 Target Token Rotation Time for Access Classes
The target token rotation time for each access class is user programmable in the range from 0 to
(2
21
)-1 octet times before prescaling, and is used in conjunction with the token rotation time at
start of access classes and ring maintenance timer. These parameters must be initialized by the
host through the initialization table and may be altered or read via the SET/READ VALUE command
thereafter. The TBC does not check that these parameters are within the specified range. There
is a set of four timers called token rotation timers which get loaded with the target token rotation
time as explained below. There is one token rotation timer for each of the lower three access
classes and one for ring maintenance. These timers all run concurrently, counting downward
from an initial value to zero, at which point their status is expired. When the station begins
processing the token at a given access class, the associated internal token rotation timer is reloaded
with the value of the target token rotation time for that access class. When the station receives
the token again it may send data from that access class until the residual time in the associated
token rotation timer has expired.
Offset
o
C
B
A
4
o
OE, 12, 16,
Target Rotation Time for Access Classes IPrescaled)
2.1.7 Token Rotation Time at Start of Ring Maintenance
The token rotation time at the start of ring maintenance is a statistic which contains the elapsed
time in units of prescaled octet times from arrival of the token to entering ring maintenance. This
statistic can be accessed by the host via the READ VALUE command.
Offset
18
o
C
B
A
Token Rotation Time at Start of Ring Maintenance IPrescaled)
2.1.8 Target Rotation Time for Ring Maintenance
The target rotation time for ring maintenance is initialized by the host through the initialization
table and may be altered or read via the SET/READ VALUE command thereafter. This parameter
gets loaded into the internal ring maintenance token rotation timer and is in the range from 0 to
(2
21 )
-1
octet times before prescaling. The station will solicit a successor if the inteLsoliciLcount
equals zero and the ring maintenance token rotation timer has not expired. If the timer has expired,
the solicitation will be deferred until the next time the station holds the token.
Offset
lA
MOTOROLA
'LA
o
C
B
A
4
Target Rotation Time for Ring Maintenance IPrescaled)
MC68824 USER'S MANUAL
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