`timescale 1ns / 1ps

module kypdDecoder(
    input logic clk,
    input logic n_rst,
    inout logic [7:0] ja, // [7:4] rows, [3:0] columns
    output logic [15:0] pressed
);
    logic [3:0] cols, rows;
    assign rows = ja[7:4]; // input
    assign ja[3:0] = cols; // output

    logic [1:0] colIndex;
    always_ff @(posedge clk) begin
        if(n_rst == 1'b0) begin
            // Zero is shifted around
            cols <= 4'b1110;
            colIndex <= 2'd0;
            pressed <= 16'b0;
        end else begin
            // Write pressed for entire row
            pressed[colIndex * 4 +: 4] = ~rows;

            // Shift zero and increment index
            cols <= {cols[2:0], 1'b1};
            colIndex <= colIndex + 1;
        end
    end
endmodule