PM7385 FREEDM-84A672
DATA SHEET
PMC-1990114
ISSUE 6
84 LINK, 672 CHANNEL FRAME ENGINE AND DATA LINK MANAGER
WITH ANY-PHY PACKET INTERFACE
Figure 3 – Partial Packet Buffer Structure
Partial Packet
Buffer RAM
Block
Pointer RAM
16 bytes
16 bytes
16 bytes
16 bytes
XX
0x03
XX
Block 0
Block 1
Block 2
Block 3
Block 0
Block 1
Block 2
Block 3
0xC8
16 bytes
16 bytes
0x01
XX
Block 200
Block 200
Block 2047
Block 2047
The partial packet buffer processor is divided into three sections: writer, reader
and roamer. The writer is a time-sliced state machine which writes the HDLC
data and status information from the HDLC processor into a channel FIFO in the
packet buffer RAM. The reader transfers channel FIFO data from the packet
buffer RAM to the downstream Receive Any-PHY Interface block (RAPI672).
The roamer is a time-sliced state machine which tracks channel FIFO buffer
depths and signals the reader to service a particular channel. If a buffer over-run
occurs, the writer ends the current packet from the HDLC processor in the
channel FIFO with an overrun flag and ignores the rest of the packet.
The FIFO algorithm of the partial packet buffer processor is based on a
programmable per-channel transfer size. Instead of tracking the number of full
blocks in a channel FIFO, the processor tracks the number of transactions.
Whenever the partial packet writer fills a transfer-sized number of blocks or writes
an end-of-packet flag to the channel FIFO, a transaction is created. Whenever
the partial packet reader transmits a transfer-size number of blocks or an end-of-
packet flag to the RAPI672 block, a transaction is deleted. Thus, small packets
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
46
PMC [ PMC-SIERRA, INC ]
