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CHAPTER 5 SAR FUNCTION
157
The "c" parameter is incremented according to the relationship between variable parameters x and y that
are managed by the
μ
PD98405, in addition to conditions (a) and (b), above, under which operation of the
shaper is enabled. The maximum value to which this parameter can be incremented is given by the value
of the C parameter, specified by the user.
The x and y variable parameters are updated by the
μ
PD98405, according to the following rule, in a 36-
clock cycle in which the scheduler checks all the shaper parameters according to the I and M parameters
specified by the user.
When x = y -> I and M are loaded into x and y, respectively.
When x > y -> I is added to x and M is added to y.
When x < y -> I is added to x.
"c" is incremented when x
≥
y. When "c" is c > 0 and p = 0, the shaper may be selected by the scheduler.
Upon being selected, a shaper enters scan status and starts transmitting cells.
Each time the shaper changes from scan status to non-scan status (i.e., when the transmission of all linked
VCs has been completed), the c parameter is decremented.
The conditions for incrementing "c" do not require that the shaper be active (the A bit of the scheduler
register is set to 1). The "c" parameter is incremented at I/M intervals until it reaches "C" (maximum)
regardless of whether the shaper has an active VC.
When the shaper is selected and enters the scan state, the "p" parameter is loaded with "P" as specified by
the user, and decremented by one each time the scheduler has dealt with all the shapers (every 36 clock
pulses). The parameter for a specific shaper must have been decremented to 0 before the scheduler can
select that shaper again. Therefore, as a minimum, the peak rate "P" must be maintained between the
cells of the same VC.