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 QX1 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 (see zra.txt).

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