RELEASED
PM7350 S/UNI DUPLEX
DATA SHEET
PMC-1980581
ISSUE 8
DUAL SERIAL LINK PHY MULTIPLEXER
in Table 16 in the cells sent on the downstream LVDS link. When the S/UNI-
DUPLEX sees that all far-end channels are congested it will immediately start
sending stuff cells on the upstream serial link (unless it has control channel cells
to send and that channel is not marked as congested). With the worst case
alignment between upstream and downstream links, the S/UNI-DUPLEX may
transmit up to two cells after the cell available deassertion was first registered by
the far-end S/UNI-VORTEX. The FIFO threshold on the S/UNI-VORTEX
accounts for this latency, buffer overflow cannot occur.
Once the far-end S/UNI-VORTEX has a chance to clear cells from its receiver
buffer it will reassert the cell available bit on all channels. Refer to the S/UNI-
VORTEX Data Sheet for further information.
Case #2: the far-end device is a S/UNI-DUPLEX
Unlike the S/UNI-VORTEX, the far-end’s S/UNI-DUPLEX’s LVDS receive buffer
is divided into 32 FIFOS, so it always individually indicates the status of the 32
user channels. This also applies to the control channel – its status in
independent of the status of the user channels.
When the near-end S/UNI-DUPLEX sees that a PHY or control channel is
congested it will take that channel out of the round robin scheduling used to
transfer cells from the buffers to the transmit LVDS link. If none of the remaining
channels have cells to send, or if all channels are experiencing congestion, then
the S/UNI-DUPLEX will automatically broadcast a stuff cell on the two upstream
serial links.
With worst case alignment between upstream and downstream links, the S/UNI-
DUPLEX may transmit up to two cells to a channel after the cell available
deassertion for that channel was first registered by the far-end S/UNI-DUPLEX.
Since the FIFO threshold on the S/UNI-DUPLEX accounts for this latency, buffer
overflow cannot occur on the active link.
Once the far-end S/UNI-DUPLEX has a chance to clear cells from the congested
receive buffer it will reassert the cell available bit on the affected channel.
9.5 Timing Reference Insertion and Recovery
The high-speed serial links are capable of transporting a timing reference
independent of the bit rate. The timing signal received on the active RXD1+/- or
RXD2+/- inputs is presented on RX8K. Rising edges of TX8K input are encoded
in the TXD1+/- and TXD2+/- cells.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
77
PMC [ PMC-SIERRA, INC ]
