bus: ari: Implement ARI interconnect groundwork

Signed-off-by: Ian M. <ian@aptel.org>

4 files changed, 202 insertions, 0 deletions

diff --git a/rtl/bus/ari_framemux.sv b/rtl/bus/ari_framemux.sv
new file mode 100644
index 0000000..9b76a51
--- /dev/null
+++ b/rtl/bus/ari_framemux.sv
@@ -0,0 +1,91 @@
+//
+// Copyright (c) 2026, Apollo Telephone Laboratories.
+// Provided under the BSD-3 clause.
+//
+
+`include "bus/ari.svh"
+
+//
+// Represents an ARI segment frame multiplexer
+//
+// @clk_i:      Clock input
+// @reset_i:    Reset input
+// @ingress_i:  Ingress frame input
+// @tap_i:      Tap port input
+// @egress_o:   Egress frame output
+//
+module ari_framemux (
+    input wire clk_i,
+    input wire reset_i,
+    input AriFrame ingress_i,
+    input AriFrame tap_i,
+
+    output AriFrame egress_o
+);
+    // Multiplexer attributes
+    parameter MUX_PERIOD   = 2;
+    parameter MUX_N_INPUT  = 2;
+    parameter MUX_N_STATES = (MUX_PERIOD * MUX_N_INPUT);
+
+    // Multiplexer states
+    parameter MUX_STATE_INGRESS0   = 0;
+    parameter MUX_STATE_INGRESS1   = 1;
+    parameter MUX_STATE_TAP0       = 2;
+    parameter MUX_STATE_TAP1       = 3;
+
+    // TDM selector
+    logic [2:0] mux_sel;
+
+    //
+    // Handle reset logic and time division multiplexing for
+    // frame routing. If there is nothing on the channel that
+    // is currently being selected, we are to route the other
+    // channel instead.
+    //
+    always_ff @(posedge clk_i) begin
+        if (reset_i) begin
+            mux_sel  <= 0;
+            egress_o <= 0;
+        end else begin
+            case (mux_sel)
+                // TDM ingress slice
+                MUX_STATE_INGRESS0: begin
+                    if (ingress_i == 0) begin
+                        egress_o  <= tap_i;
+                    end else begin
+                        egress_o  <= ingress_i;
+                    end
+                end
+                MUX_STATE_INGRESS1: begin
+                    if (ingress_i == 0) begin
+                        egress_o  <= tap_i;
+                    end else begin
+                        egress_o  <= ingress_i;
+                    end
+                end
+
+                // TDM tap slice
+                MUX_STATE_TAP0: begin
+                    if (tap_i == 0) begin
+                        egress_o <= ingress_i;
+                    end else begin
+                        egress_o <= tap_i;
+                    end
+                end
+                MUX_STATE_TAP1: begin
+                    if (tap_i == 0) begin
+                        egress_o <= ingress_i;
+                    end else begin
+                        egress_o <= tap_i;
+                    end
+                end
+            endcase
+        end
+
+        if (!reset_i && mux_sel < MUX_N_STATES) begin
+            mux_sel <= mux_sel + 1;
+        end else if (!reset_i && mux_sel >= MUX_N_STATES) begin
+            mux_sel <= 0;
+        end
+    end
+endmodule
diff --git a/rtl/bus/ari_mainbus.sv b/rtl/bus/ari_mainbus.sv
new file mode 100644
index 0000000..225fa03
--- /dev/null
+++ b/rtl/bus/ari_mainbus.sv
@@ -0,0 +1,26 @@
+//
+// Copyright (c) 2026, Apollo Telephone Laboratories.
+// Provided under the BSD-3 clause.
+//
+
+`include "bus/ari.svh"
+
+//
+// On-chip mainbus
+//
+// @clk_i:    Clock input
+// @reset_i:  Reset input
+// @r_tap_i:  Request taps
+//
+module ari_mainbus (
+    input wire clk_i,
+    input wire reset_i,
+    input AriFrame r_tap_i[0:ARI_SEGMENT_COUNT-1]
+);
+    // Request ring
+    ari_ring req_ring (
+        .clk_i(clk_i),
+        .reset_i(reset_i),
+        .tap_i(r_tap_i)
+    );
+endmodule
diff --git a/rtl/bus/ari_ring.sv b/rtl/bus/ari_ring.sv
new file mode 100644
index 0000000..48062c7
--- /dev/null
+++ b/rtl/bus/ari_ring.sv
@@ -0,0 +1,52 @@
+//
+// Copyright (c) 2026, Apollo Telephone Laboratories.
+// Provided under the BSD-3 clause.
+//
+
+`include "bus/ari.svh"
+
+//
+// Represents a ring of ARI segments which forms a single
+// bus channel.
+//
+// @clk_i:      Clock input
+// @reset_i:    Reset input
+// @tap_i:      Segment taps
+//
+module ari_ring (
+    input wire clk_i,
+    input wire reset_i,
+    input AriFrame tap_i[0:ARI_SEGMENT_COUNT-1]
+);
+    // Segment feeders
+    AriFrame seg3_feed;
+    AriFrame seg2_feed;
+    AriFrame seg1_feed;
+
+    // Segment 0
+    ari_segment seg0 (
+        .clk_i(clk_i),
+        .reset_i(reset_i),
+        .ingress_i(seg3_feed),
+        .tap_i(tap_i[0]),
+        .egress_o(seg1_feed)
+    );
+
+    // Segment 1
+    ari_segment seg1 (
+        .clk_i(clk_i),
+        .reset_i(reset_i),
+        .ingress_i(seg1_feed),
+        .tap_i(tap_i[1]),
+        .egress_o(seg2_feed)
+    );
+
+    // Segment 2
+    ari_segment seg2 (
+        .clk_i(clk_i),
+        .reset_i(reset_i),
+        .ingress_i(seg2_feed),
+        .tap_i(tap_i[2]),
+        .egress_o(seg3_feed)
+    );
+endmodule
diff --git a/rtl/bus/ari_segment.sv b/rtl/bus/ari_segment.sv
new file mode 100644
index 0000000..0523101
--- /dev/null
+++ b/rtl/bus/ari_segment.sv
@@ -0,0 +1,33 @@
+//
+// Copyright (c) 2026, Apollo Telephone Laboratories.
+// Provided under the BSD-3 clause.
+//
+
+`include "bus/ari.svh"
+
+//
+// Represents an ARI segment that routes bus data
+//
+// @clk_i:      Clock input
+// @reset_i:    Reset input
+// @ingress_i:  Ingress frame input
+// @tap_i:      Tap port input
+// @egress_o:   Egress frame output
+//
+module ari_segment (
+    input wire clk_i,
+    input wire reset_i,
+    input AriFrame ingress_i,
+    input AriFrame tap_i,
+
+    output AriFrame egress_o
+);
+    // Frame multiplexer
+    ari_framemux fmux (
+        .clk_i(clk_i),
+        .reset_i(reset_i),
+        .ingress_i(ingress_i),
+        .tap_i(tap_i),
+        .egress_o(egress_o)
+    );
+endmodule