# Mirocom QXI interconnect

The Mirocom Quick Looped Interconnect (QXI) is the standard for Network-on-Chip interconnects within the Mirocom space.  
  
Terminology

Ringstop:  
 A ringstop is an single interconnecting endpoint on a ringbus and is  
 responsible for handling time-division multiplexing of the ingress  
 passdown link and passdown injection to the egress passdown link.

Passdown link:  
 A passdown link is an connection that passes through one ringstop to  
 the next, forming a feedback loop that allows the bus to circularly  
 propagate packets.

Passdown injection:  
 Passdown injection allows for a node on the bus to inject its own packets  
 into a ringstop.

##### Architectural overview

The Mirocom QXI fabric is a high-performance dual ring interconnect that incorporates  
zero-relative addressing such that each node can be identified with a 5-bit region  
identifier and addressed with a 27-bit offset, both of which are encoded in a 32-bit  
physical address. In a typical configuration, one ring will be going clockwise and meant for requests  
while the other ring goes counter clockwise and meant for data responses.

The QXI fabric is considered a Network-on-Chip that speaks QXI packets. A QXI packet frame encapsulates  
metadata such as a CRC32 checksum, sequence number, packet kind, destination node, source node as well  
as the packet payload and more.

##### Physical address format

 offset region  
+-------+-----+  
| 31:5 | 4:0 | bits  
+-------+-----+

##### High-level diagrammatic representation of a single ring

  
 1 \[PD\_0\]  
 \[PDI\_0\] --> \[RS\_0\] ---/----> \[RS\_1\] <-- \[PDI\_1\]  
 ^ |\_ 2 \[PD\_1\]  
 |\_4 |  
 | 3 \[PD\_1\] V  
 \[PDI\_3\] --> \[RS\_3\] <-/------ \[RS\_2\] <-- \[PDI\_2\]  
 =========================  
 Where:  
 RS\_N => Ringstop  
 PD\_N => Passdown link  
 PDI\_N => Passdown link injection