S/UNI®-ATLAS-3200 Telecom Standard Product Data Sheet
Preliminary
The S/UNI-ATLAS-3200 input interface must behave as the Tx PHY layer device on the POS-
PHY bus. As the PHY-layer, its function is to accept information sent by the Link-layer, to
respond to polling on TPP_ADDR with the appropriate packet available (buffer) status on
TPP_PTPA, and to provide backpressure on the selected port on TPP_STPA. The TxPhy block,
assisted by the SDQ block (see below) performs the above functions. Its configuration registers
may be found in Section 11.7.
The S/UNI-ATLAS-3200 must behave as a Tx Link-layer on the POS-PHY bus. As the Link-
layer, it controls the flow of information to the PHY Layer device, by polling the PHY Layer
device to obtain packet available (buffer) status. Polling is performed in a weighed round-robin
fashion controlled by a software-configurable calendar. Once the Cell Available information has
been collected through polling, port selection is performed using the same calendar. The calendar
is programmed via the TxLink block’s Calendar Address and Data Register, and is described in
Section 10.1.7. When a PHY is serviced, it is permitted to transfer one ATM cell or POS-PHY
packet, or an amount of data equal to the programmed Burst Size for that PHY, whichever is less.
The TxLink block can map internal PHY addresses to different external PHY addresses via a
user-programmable port map, as described in Section 10.1.6. The TxLink block, assisted by the
SDQ block (see below) performs the above functions. Its configuration registers may be found in
Section 11.10.
10.1.5 Polling and Servicing Calendar
Polling and servicing of PHY queues is performed in a weighted round-robin fashion. The order
of the polling, and the relative weighting of different PHYs is directly configured by writing a
calendar to each of the interface blocks that supports polling or servicing. The calendar is a
circular list of PHY IDs. When polling, the poller continuously presents the PHY IDs in the order
shown in the calendar, and records the resulting Cell/Buffer Available signals. The more often a
given PHYID appears in the calendar, the more often it gets polled. The length of the calendar is
configurable, and the maximum length of the calendar is 128 entries, to allow considerable
flexibility in weighting the 48 possible PHYs. Servicing is done in exactly the same way as
polling, using the same calendar. When the time comes to select the next cell or packet to
transmit, the interface block scrolls forward from its current position through the PHY IDs in the
calendar until it finds one that can transfer a cell. The more often a PHY ID appears in the
calendar, the more frequently it will be serviced, assuming it is enabled and offers traffic. Table 3
below illustrates a simple, 16-long calendar for three STS-12 connections (PHYs 0, 1, and 2) and
four STS-3 connections (PHYs 3, 4, 5, and 6). Note how the STS-12 connections have four times
as many entries as the STS-3 connections. Note also that the entries for any given PHY are
distributed evenly throughout the calendar in order to ensure maximum usefulness of the polling
and maximum fairness of the servicing.
Table 3 Polling and Servicing Calendar Example
Calendar
Address
0
1
2
3
Calendar Data
0
1
2
3
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990553, Issue 4
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PMC [ PMC-SIERRA, INC ]
