Added JTAG interface with testbench

rtl/arch/spartan-6/jtag_if.v

@@ -0,0 +1,34 @@
+`timescale 1ns/1ps
+
+// =============================================================================
+// JTAG interface
+// Spartan-6 BSCAN primitive wrapper (USER1 chain).
+// =============================================================================
+module jtag_if #(
+    parameter chain = 1
+)(
+    input wire i_tdo,
+    output wire o_tck,
+    output wire o_tdi,
+    output wire o_drck,
+    output wire o_capture,
+    output wire o_shift,
+    output wire o_update,
+    output wire o_runtest,
+    output wire o_reset,
+    output wire o_sel
+);
+    BSCAN_SPARTAN6 #(
+        .JTAG_CHAIN(chain)
+    ) bscan_i (
+        .CAPTURE(o_capture),
+        .DRCK(o_drck),
+        .RESET(o_reset),
+        .RUNTEST(o_runtest),
+        .SEL(o_sel),
+        .SHIFT(o_shift),
+        .TCK(o_tck),
+        .TDI(o_tdi),
+        .UPDATE(o_update)
+    );
+endmodule

rtl/core/jtag_if.v

@@ -0,0 +1,34 @@
+`timescale 1ns/1ps
+
+// =============================================================================
+// JTAG interface
+// Generic stub model with inactive/tied-off outputs.
+// =============================================================================
+module jtag_if #(
+    parameter chain = 1
+)(
+    input wire i_tdo,
+    output wire o_tck,
+    output wire o_tdi,
+    output wire o_drck,
+    output wire o_capture,
+    output wire o_shift,
+    output wire o_update,
+    output wire o_runtest,
+    output wire o_reset,
+    output wire o_sel
+);
+    assign o_tck = 1'b0;
+    assign o_tdi = 1'b0;
+    assign o_drck = 1'b0;
+    assign o_capture = 1'b0;
+    assign o_shift = 1'b0;
+    assign o_update = 1'b0;
+    assign o_runtest = 1'b0;
+    assign o_reset = 1'b0;
+    assign o_sel = 1'b0;
+
+    // Keep lint tools quiet in generic builds where TDO is unused.
+    wire _unused_tdo;
+    assign _unused_tdo = i_tdo;
+endmodule

rtl/toplevel/top_jtag.v

@@ -0,0 +1,131 @@
+module top_jtag(
+    input wire aclk,
+    input wire aresetn,
+
+    output wire led_green,
+    output wire led_red,
+    output wire [7:0] LED,
+
+    output wire [5:0] r2r
+);
+    // Clocking
+    wire clk_100;
+    wire clk_15;
+    assign clk_100 = aclk;
+    clk_gen clocking(
+        .clk_in(clk_100),
+        .clk_out_15(clk_15)
+    );
+
+    localparam integer JTAG_DATA_BITS = 8;
+    wire [JTAG_DATA_BITS-1:0] jtag_data;
+
+    jtag_write_reg #(
+        .DATA_BITS(JTAG_DATA_BITS),
+        .CHAIN(1)
+    ) jtag_writer (
+        .clk_i(clk_15),
+        .rst_n_i(aresetn),
+        .data_o(jtag_data)
+    );
+
+    assign LED = jtag_data[7:0];
+    assign led_green = jtag_data[0];
+    assign led_red = jtag_data[7];
+    assign r2r = jtag_data[5:0];
+
+endmodule
+
+module jtag_write_reg #(
+    parameter integer DATA_BITS = 8,
+    parameter integer CHAIN = 1
+)(
+    input wire clk_i,
+    input wire rst_n_i,
+    output reg [DATA_BITS-1:0] data_o
+);
+    wire jtag_tck;
+    wire jtag_tdi;
+    wire jtag_drck;
+    wire jtag_capture;
+    wire jtag_shift;
+    wire jtag_update;
+    wire jtag_runtest;
+    wire jtag_reset;
+    wire jtag_sel;
+    reg [DATA_BITS-1:0] shift_q;
+    reg [DATA_BITS-1:0] data_jtag_q;
+    reg update_toggle_jtag_q;
+    reg update_toggle_meta_q;
+    reg update_toggle_sync_q;
+    reg update_toggle_sync_d_q;
+    reg [DATA_BITS-1:0] data_meta_q;
+    reg [DATA_BITS-1:0] data_sync_q;
+
+    jtag_if #(
+        .chain(CHAIN)
+    ) jtag (
+        .i_tdo(shift_q[0]),
+        .o_tck(jtag_tck),
+        .o_tdi(jtag_tdi),
+        .o_drck(jtag_drck),
+        .o_capture(jtag_capture),
+        .o_shift(jtag_shift),
+        .o_update(jtag_update),
+        .o_runtest(jtag_runtest),
+        .o_reset(jtag_reset),
+        .o_sel(jtag_sel)
+    );
+
+    always @(posedge jtag_drck or posedge jtag_reset or negedge rst_n_i) begin
+        if (!rst_n_i || jtag_reset) begin
+            shift_q <= {DATA_BITS{1'b0}};
+        end else if (jtag_sel && jtag_capture) begin
+            shift_q <= data_jtag_q;
+        end else if (jtag_sel && jtag_shift) begin
+            if (DATA_BITS == 1) begin
+                shift_q <= jtag_tdi;
+            end else begin
+                shift_q <= {jtag_tdi, shift_q[DATA_BITS-1:1]};
+            end
+        end
+    end
+
+    always @(posedge jtag_update or posedge jtag_reset or negedge rst_n_i) begin
+        if (!rst_n_i || jtag_reset) begin
+            data_jtag_q <= {DATA_BITS{1'b0}};
+            update_toggle_jtag_q <= 1'b0;
+        end else if (jtag_sel) begin
+            data_jtag_q <= shift_q;
+            update_toggle_jtag_q <= ~update_toggle_jtag_q;
+        end
+    end
+
+    // CDC into clk_i domain: toggle synchronize + stable data sampling.
+    always @(posedge clk_i or negedge rst_n_i) begin
+        if (!rst_n_i) begin
+            update_toggle_meta_q <= 1'b0;
+            update_toggle_sync_q <= 1'b0;
+            update_toggle_sync_d_q <= 1'b0;
+            data_meta_q <= {DATA_BITS{1'b0}};
+            data_sync_q <= {DATA_BITS{1'b0}};
+            data_o <= {DATA_BITS{1'b0}};
+        end else begin
+            update_toggle_meta_q <= update_toggle_jtag_q;
+            update_toggle_sync_q <= update_toggle_meta_q;
+            update_toggle_sync_d_q <= update_toggle_sync_q;
+            data_meta_q <= data_jtag_q;
+            data_sync_q <= data_meta_q;
+
+            if (update_toggle_sync_q ^ update_toggle_sync_d_q) begin
+                data_o <= data_sync_q;
+            end
+        end
+    end
+
+    // Not used for this simple write-register, but kept for completeness.
+    wire _unused_tck;
+    wire _unused_runtest;
+    assign _unused_tck = jtag_tck;
+    assign _unused_runtest = jtag_runtest;
+endmodule