PMC-Sierra, Inc.
PRELIMINARY
PM5381 S/UNI-2488
DATASHEET
PMC-2000489
ISSUE 1
SATURN USER NETWORK INTERFACE FOR 2488 MBIT/S
This threshold is set in 16 byte Blocks. This threshold can never be greater than the size of
the FIFO being configured, and the absolute maximum value is DT[7:0] +1 = 192. This
number should be a standard fraction of the FIFO size in blocks. In the case of ATM FIFOs,
this number should be set to a value of DT[7:0] = 3 (ATM cells are 4 Blocks long).
The DT[7:0] threshold sets the level at which the cell/packet processors (TCFP) blocks can
begin transmission of a cell or packet. Once transmission of a cell or packet begins, it cannot
be stopped so this threshold should be set to a value which guarantees that the Utopia/POS-
PHY interface can write to the FIFO in due time to prevent FIFO underruns. For packet data,
it is recommended that DT[7:0] be set to a larger value about equal to 1/2 or 2/3 the size of
the FIFO.
Proprietary and Confidentail to PMC-Sierra Inc., and for its Customer’s Internal Use
359
PMC [ PMC-SIERRA, INC ]
