IDT Switch Description
Revision 1.5
Integrated Device Technology, Inc.
CPS-16/12/8 User Manual
3 - 5
July 10, 2012
2) If the highest priority packet in the retransmit buffer (unicast OR multicast) has priority N, and a
unicast or multicast packet of priority > N is being offered to the retransmit buffer by the switch's
txbuf, then the retransmit buffer must accept the packet from the TXBUFs.
Also, the following behavior is standard:
Multicast Split:
If rx port B receives a packet (call it PC) of priority M (where M <= N) tar-
geted for tx port A, but port A cannot receive it due to the conflict resulting from PA described
above, then PC will remain in the input buffer but it will continue multicast to other available tx
port. All subsequent packets (multicast or unicast) received at rx port B with priority => M tar-
geted for other tx port will still switch over. For the subsequent packet with priority < M targeted
for ANY tx port will delayed until packet PB can be forwarded to the switch. PC will not remove
from the input buffer until port A is available to receive new packet.
3.4.2.3 Re-Transmission MIMIC
The intent of RT-mimic was to allow for streaming data application where low-latency is preferable even at
the cost of occasional packet loss. It is implemented by not storing packets in the retransmit buffer. In this
way, if a retry was received because the link partner has a full input buffer or if a NAK was received because
of a transmission error, then CPS would simple resent the next available packet instead of retransmitting
the previous one. RT-mimic affects behavior on the output-port only and all packet traffic if it is enabled.
3.5 FLOW CONTROL AND CONGESTION MANAGEMENT
3.5.1 Flow Control Internal
Internally, self defined protocol coordinate each module. The flow control is always companioned with data
in the anti-direction. Data is moving from input buffer to output buffer, flow control is send from output buffer
to input buffer. Quick transportation and quick response minimize the buffer dimension.
3.5.2 Flow Control External
The CPS family SRIO port supports receiver based flow control. (See sRIO spec for detail information
about receiver based flow control)
For multicast, sRIO specification is limited to request transactions that do not require responses,
such as SWRITE transactions. So it is user’s responsibility to multicast non-response packet.
The CPS will blindly forward packet based on the ID and routing table. If user multicast a trans-
actions with responses, the CPS will not drop any response. All responses will forward to the
sender base on the DestID.
