IDT sRIO Ports
Revision 1.5
Integrated Device Technology, Inc.
CPS-16/12/8 User Manual
2 - 3
July 10, 2012
In addition, these registers supports the ability to reset lanes in the quad and to force a reinitialization of
lanes in the enhanced quad. The ability to control reset and initialization of lanes 0 and 1 versus lanes 2 and
3 through these registers are also provided.
2.1.4 Packet Forwarding
2.1.4.1 Store and Forward
CPS supports a “Store and Forward” methodology for packet forwarding. This methodology consist of vali-
dation of each received packet to the SRIO specifications (including a successful CRC verification) before
the packet is forwarded via the output port referenced by the destination ID in the packet header.
2.1.4.2 Cut Through
CPS supports “Cut Through” packet forwarding methodology. This methodology provides the ability to
begin forwarding a packet via its referenced output port before it has been validated. Packets that have
been found to be invalid after transmission has begun, is terminated with the SRIO STOMP control symbol
which will be used in compliance with the rev 1.3 SRIO protocol standard. Assuming no starvation and no
output port contention, the first byte in to first byte out latency for a maximum sized packet will be the same
as that for a minimum sized packet.
Packet counters are implemented such that packets which are STOMPED are not included in the count.
Note that Cut Through mode supports the use of the retransmit buffer for reliable transport as defined in the
SRIO protocol specification.
If a Cut Through packet is being transmitted and the transmission becomes starved for data (part of the
packet has been transmitted but the rest of the packet is not available for transmission) EOP control symbol
will be transmitted within the packet (i.e within the boundary of the packet’s SOP and EOP) until the rest (or
more) of the packet becomes available for transmission.
Cut Through is disabled at reset of the device. This mode is enabled globally via a maintenance write
command to the CUT_THRU_ENABLE bit of the CPS_CONTROL register. If this bit is set, Cut Through
forwarding methodology will be enabled for all CPS ports.
When Cut Through is enabled the devices’ output packet scheduler will consider a packet as available for
transmission/forwarding as soon as enough of the packet (i.e. the destination ID has been received and
decoded) to determine which port to use for transmission. The device does not use full packet reception as
a criteria to determine when a packet is available for transmission.
2.1.5 Port Statistics (Packet Counter)
The CPS provides the ability to generate statistics at each port. Each port provides a 32-bit packet counter
for each of the following data at that given port:
1) Ack Counter: Number of Packet-accepted control symbol has been sent; number of packet has
been successfully received.
2) Nack Counter: Number of Packet-not-accepted control symbol and packet-retry control symbol
sent. Note, during the initialization and re-initialization, it may cause some Nack count. User should
clear the Nack count after port initialization.
3) Switch Counter: Number of packets successfully sent out
3) Trace Counter: Packets which have met port’s trace criteria (when enabled)
4) Filter Counter: Packets which have been filtered
All counters will reset to 0 when read, and will hold their maximum value (saturate) when it is reached.
2.2 TRACE FUNCTION
Each port supports the ability to compare a configurable set of parameters in a given received packet
against a set of configurable predefined values and, if a match occurs, routes the packet to a configurable
output port. This function is defined as the “Trace” function.
