4. Internal Switching Fabric > Packet Queuing
98
Tsi578 User Manual
June 6, 2016
Integrated Device Technology
www.idt.com
Reorder limiting prevents excessive delays of a packet by packets of lower or equal priority. Reorder
limiting does not prevent delays of a packet by packets of higher priority. When reorder limiting is
enabled, each time a packet X is delayed in the queue because a lower or same priority packet was sent
earlier, the fabric decrements the reorder counter. When the packet reordered ahead of packet X has a
higher priority than packet X, the reorder counter of packet X is not decremented. Refer to
for more information.
When the reorder counter for packet X reaches 0, no packets of lower or same priority are permitted to
be reordered ahead of packet X. When the reorder counter of packet X is 0, packet X must be
transmitted ahead of all other packets of lower or equal priority that are positioned after packet X in the
queue.
One of the properties of reorder limiting is that when the reorder counter of a packet X of given priority
Y reaches 0, the reorder counters of all packets with a priority equal or greater than Y that appear ahead
of packet X in the queue must also be 0.
Reorder limiting is disabled by default and can be enabled by setting the RDR_LIMIT_EN bit to 1 in
the
“Fabric Control Register” on page 380
. Enabling this feature is recommended. Note that reorder
limiting applies to all ports and all packets in the Tsi578.
The number of times a packet is permitted to be delayed by a lower or same priority packet is
configurable through the RDR_LIMIT register field in the
“Fabric Control Register” on page 380
Note that reorder limiting can change the packet chosen by FCFS and Strict Priority 1 arbitration. For
example, assume three packets, X1, X2 and X3, are held in the ingress queue in that order. Packets X1
and X2 have the same priority, and packet X3 has a higher priority. Packet X1 and X3 cannot make
progress. Using Strict Priority 1 arbitration without reorder limiting results in packet X2 being
reordered to the head of the queue. However, if the reorder limiting is used, and packet X1’s reorder
limit counter has reached 0, then the Strict Priority 1 arbitration algorithm cannot select packet X2.
Packet X3 is chosen in this case.
Higher priority packets which appear after packet X in the queue can cause the continued
delay of packet X.
Higher priority packets can always be reordered ahead of packet X, whatever the value of the
reorder counter of packet X.
Содержание Tsi578
Страница 1: ...IDT Tsi578 Serial RapidIO Switch User Manual June 6 2016 Titl ...
Страница 20: ...About this Document 20 Tsi578 User Manual June 6 2016 Integrated Device Technology www idt com ...
Страница 102: ...4 Internal Switching Fabric Packet Queuing 102 Tsi578 User Manual June 6 2016 Integrated Device Technology www idt com ...
Страница 228: ...11 Signals Pinlist and Ballmap 228 Tsi578 User Manual June 6 2016 Integrated Device Technology www idt com ...
Страница 504: ...B Clocking P_CLK Programming 504 Tsi578 User Manual June 6 2016 Integrated Device Technology www idt com ...
Страница 526: ...Index 526 Tsi578 User Manual June 6 2016 Integrated Device Technology www idt com ...