
DATA SHEET
PM7367 FREEDM-32P32
ISSUE 2
PMC-1991499
FRAME ENGINE AND DATA LINK MANAGER
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMER’S INTERNAL USE
31
Figure 2 – CRC Generator
D
0
D
1
g
1
D
2
D
n-1
Message
Parity Check Digits
g
2
g
n-1
LSB
MSB
8.2 Receive Channel Assigner
The Receive Channel Assigner block (RCAS) processes up to 32 serial links.
Each link is independent and has its own associated clock. For each link, the
RCAS performs a serial to parallel conversion to form data bytes. The data
bytes are multiplexed, in byte serial format, for delivery to the Receive HDLC
Processor / Partial Packet Buffer block (RHDL) at SYSCLK rate. In the event
where multiple streams have accumulated a byte of data, multiplexing is
performed on a fixed priority basis with link #0 having the highest priority and link
#31 the lowest.
Links containing a T1 or an E1 stream may be channelised. Data at each time-
slot may be independently assigned to a different channel. The RCAS performs
a table lookup to associate the link and time-slot identity with a channel. T1 and
E1 framing bits/bytes are identified by observing the gap in the link clock which is
squelched during the framing bits/bytes. For unchannelised links, clock rates are
limited to 52 MHz on link #0 to #2 and limited to 10 MHz for the remaining links.
All data on each link belongs to one channel. For the case of two unchannelised
links, the maximum link rate is 45 MHz for SYSCLK at 25 MHz and 52 MHz for
SYSCLK at 33 MHz. For the case of more numerous unchannelised links or a
mixture of channelise with unchannelised links, the total instantaneous link rate
over all the links is limited to 64 MHz. The RCAS performs a table lookup using
only the link number to determine the associated channel, as time-slots are
non-existent in unchannelised links.
The RCAS provides diagnostic loopback that is selectable on a per channel
basis. When a channel is in diagnostic loopback, stream data on the received
links originally destined for that channel is ignored. Transmit data of that channel
is substituted in its place.