Create chain1.v

src/chain1.v

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+/*  
+    SPDX-FileCopyrightText: 2024 Harald Pretl
+    Johannes Kepler University, Institute for Integrated Circuits
+    SPDX-License-Identifier: Apache-2.0
+
+   Very simple scan chain with load register and magic cookie detection for
+   SG13G2 May'2024 run. Target is to test RTL2GDS flow for functionality. 
+
+   The output o_check is XOR of i_dat and i_load (pure logic in case all else
+   fails).
+
+   8 pins available on testchiplet:
+
+    1 = VDD
+    2 = VSS
+    3 = i_clk (like SPI SCLK)
+    4 = i_dat (like SPI MOSI)
+    5 = i_load (like SPI nCS)
+    6 = o_dat (like SPI MISO)
+    7 = o_det (magic cookie detected)
+    8 = o_check (XOR of i_dat and i_load)
+*/
+
+`ifndef __CHAIN1__
+`define __CHAIN1__
+`default_nettype none
+
+module chain1 (
+    input wire          i_clk,
+    input wire          i_dat,
+    input wire          i_load,
+    output wire         o_dat,
+    output wire         o_det,
+    output wire         o_check,
+    output wire [15:0]  o_data
+);
+
+    reg [15:0] scan_r, data_r;
+
+    // here we see if the stored content is matching a magic cookie
+    assign o_det = (data_r === 16'hcafe) ? 1'b1 : 1'b0;
+    // provide loaded data
+    assign o_data = data_r;
+    // shift out MSB register bit
+    assign o_dat = scan_r[15];
+
+    // here the scan chain, shift MSB first (as in SPI)
+    always @(posedge i_clk) begin
+        if (i_load === 1'b0)
+            scan_r <= {scan_r[14:0],i_dat};
+    end
+
+    // and here we latch the result
+    always @(posedge i_load) begin
+        data_r <= scan_r;
+    end
+
+    // here a very simple boolean function to check basic functionality
+    assign o_check = i_dat ^ i_load;
+
+endmodule // chain1
+`endif 
+