8. Performance > Port-to-Port Performance Characteristics
194
Tsi578 User Manual
June 6, 2016
Integrated Device Technology
www.idt.com
The Tsi578 is designed to allow high priority traffic to bypass low priority traffic in periods of
contention, as allowed in the RapidIO protocol specification.
8.4.2
Packet Throughput Performance
Packet throughput varies from the packet type (for example, NWRITE packets do not require a logical
layer response), availability of resources within the device, ability for source and destination of traffic
to generate or receive packets, retries of packet, and actual data rates.
A
bubble
is a control symbol inserted by an egress port to maintain the baud rate of the port. The
appearance of a bubble indicates that the egress port is under-utilized.
8.4.2.1
One Port-to-One Port Throughput Performance
Under a non-congested port-to-port packet traffic situation, when the ingress and egress have the same
line rate (1.25, 2.5, or 3.125 Gbaud), the ingress and egress always maintain the line rates. This means
there is no retry of packets at the ingress ports and no bubbles will appear in the egress packet stream
except for the idle sequence insertion every 5000 code-groups as required by the
RapidIO Interconnect
Specification (Revision 1.3)
. This is true for any payload size and different priorities.
When the ingress line rate exceeds that of the egress port, a retry occurs at the ingress port when the
buffer is filled to the capacity permitted by the priority of the packets. The egress port still maintains its
maximum packet rate with no bubble. This is true for any payload size and priorities.
Table 24: 4x/1x Latency Numbers Under No Congestion
Reference Clock
Ingress and Egress
Port Width
Ingress and Egress
Baud Rate
Minimum Latency (ns)
a
a.
Due to the asynchronous ability of the clock frequencies within the device, the latency numbers can vary as
much by
o
ne 312.5 MHz clock period and one reference clock (S_CLK) period.
156.25MHz
4x mode
3.125
112
2.5
128.8
1.25
212.8
1x mode
3.125
131.2
2.5
152.8
1.25
260.8
A bubble packet is not the Idle Sequence inserted to maintain link synchronization, as
required by the
RapidIO Interconnect Specification (Revision 1.3)
.