PXB4330 Datasheet, PDF (141/201 Pages) Infineon Technologies AG – ICs for Communications

PXB 4330
Register Descriptions
MaxBurstS(3:0)
Maximum Burst size for a Scheduler
Per scheduler cell bursts can occur due to previously unused cell
cycles. Each scheduler has an event generator that determines
when this scheduler should be served based on the programmed
scheduler rates. Because several schedulers share one UTOPIA
interface, it may happen that events cannot be served immediately
due to active cell transfers of previous events. Such ’unused cell
cycles’ are counted (see also registers SCTIU/SCTID on page 6-
137) and can be used for later cell bursts allowing a near 100%
scheduler rate utilization. Cell bursts due to this mechanism are not
rate limited.
The maximum burst size, generated due to previously counted
’unused cell cycles’, is controlled by bit field MaxBurstS(3:0) in the
range 0..15 cells (a minimum value of 1 is recommended).
Maximum burst size dimensioning depends on the burst tolerance
of subsequent devices (buffer capacity and backpressure
capability).
E.g. if PHY(s) connected to the ABM do not support backpressure
and provide a 3 cell transmit buffer, a value in the range 1..3 is
recommended to avoid PHY buffer overflows resulting in cell losses
(e.g. typical for ADSL PHYs connected to the ABM).
If a PHY is connected that supports port specific backpressure to
prevent its transmit buffers from overflowing or provides sufficient
buffering, the maximum value of 15 can be programmed
guaranteeing a near 100% scheduler rate utilization.
Data Sheet
6-141
09.99