commit 8ccea9566e7bca674e7f910deea2fecc7925fc4e
Author: Denis Tereshkin <denis@kasan.ws>
Date:   Thu Nov 23 22:26:50 2023 +0700

    Add ALU

diff --git a/doc/w65c02s.pdf b/doc/w65c02s.pdf
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index 0000000..cef921f
Binary files /dev/null and b/doc/w65c02s.pdf differ
diff --git a/src/alu.verilog b/src/alu.verilog
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+++ b/src/alu.verilog
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+module alu
+  (
+   input            nrst,
+   input            clk,
+   input [7:0]      A,
+   input [7:0]      B,
+   input            C,
+   input [2:0]      sel,
+   output [7:0] result,
+   output r_n,
+   output r_z,
+   output reg r_v,
+   output reg r_c
+   );
+
+   localparam OP_OR = 0;
+   localparam OP_AND = 1;
+   localparam OP_EOR = 2;
+   localparam OP_ADC = 3;
+   localparam OP_SUB = 4;
+   localparam OP_ROT = 5;
+   localparam OP_SHF = 6;
+
+   localparam SHIFT_LEFT = 0;
+   localparam SHIFT_RIGHT = 1;
+
+   wire        rst = !nrst;
+   reg [8:0] buffer;
+   wire [8:0] sum;
+   wire [8:0] diff;
+   
+   assign result[7:0] = buffer[7:0];
+   assign r_z = buffer[7:0] == 0;
+   assign r_n = buffer[7];
+   assign sum = A + B + C;
+   assign diff = A - B - (1 - C);
+
+   always @(posedge clk)
+     begin
+        case (sel)
+          OP_OR:
+            begin
+               buffer <= A | B;
+            end
+          OP_AND:
+            begin
+               buffer <= A & B;
+            end
+          OP_EOR:
+            begin
+               buffer <= A ^ B;
+            end
+          OP_ADC:
+            begin
+               buffer <= sum;
+               r_c <= sum[8];
+               r_v <= !(A[7] ^ B[7]) & (A[7] & sum[7]);
+            end
+          OP_SUB:
+            begin
+               buffer <= diff;
+               r_c <= diff[8];
+               r_v <= !(A[7] ^ B[7]) & (A[7] & diff[7]);
+            end
+          OP_ROT:
+            begin
+               if (B == SHIFT_LEFT) begin
+                  buffer[8:1] <= A[7:0];
+                  buffer[0] <= C;
+                  r_c <= A[7];
+                 end
+               else begin
+                  buffer[6:0] <= A[7:1];
+                  buffer[7] <= C;
+                  r_c <= A[0];
+                end
+            end
+          OP_SHF:
+            begin
+               if (B == SHIFT_LEFT) begin
+                  buffer[8:1] <= A[7:0];
+                  buffer[0] <= 0;
+                  r_c <= A[7];
+                 end
+               else begin
+                  buffer[6:0] <= A[7:1];
+                  buffer[7] <= 0;
+                  r_c <= A[0];
+                end
+            end
+        endcase // case sel
+     end
+
+endmodule
diff --git a/tests/test_alu.verilog b/tests/test_alu.verilog
new file mode 100644
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+++ b/tests/test_alu.verilog
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+module test_alu;
+   initial begin
+      $dumpfile("test.vcd");
+      $dumpvars(0, test_alu);
+   end
+
+`define assert(signal, value) \
+if (signal !== value) begin \
+   $display("ASSERTION FAILED in %m: signal != value"); \
+     $finish; \
+       end
+
+
+   reg nrst = 1;
+   reg clk = 0;
+
+   reg [7:0] A;
+   reg [7:0] B;
+   reg       C;
+   reg [2:0] op_sel;
+
+   wire [7:0] result;
+   wire       r_z;
+   wire       r_n;
+   wire       r_c;
+   wire       r_v;
+
+   always #1 clk = !clk;
+
+   alu my_alu(
+              .nrst(nrst),
+              .clk(clk),
+              .A(A),
+              .B(B),
+              .C(C),
+              .sel(op_sel),
+              .result(result),
+              .r_z(r_z),
+              .r_n(r_n),
+              .r_c(r_c),
+              .r_v(r_v));
+
+   initial begin
+      #10 A = 8'h11;
+      B = 8'h22;
+      C = 0;
+      op_sel = 0; // OR
+
+      #2 `assert (result, 8'h33);
+
+      #2 op_sel = 1; // AND
+
+      #2 `assert (result, 8'h00);
+
+      #2 op_sel = 2; // EOR
+
+      #2 `assert (result, 8'h33);
+
+      #2  A = 8'h22;
+      B = 8'h22;
+
+      #2 `assert (result, 8'h00);
+
+      #2 op_sel = 3; // ADC
+
+      #2  A = 8'h22;
+      B = 8'h22;
+
+      #2 `assert (result, 8'h44);
+
+      #2 C = 1; // ADD with CARRY
+
+      #2 `assert (result, 8'h45);
+
+      #2  A = 8'hf0;
+      B = 8'h10;
+      C = 0;
+
+      #2 `assert (r_c, 1);
+
+      #2 op_sel = 4;
+      A = 8'hf0;
+      B = 8'h10;
+      C = 0;
+      #2 `assert (result, 8'hdf);
+
+      #2 C = 1;
+
+      #2 `assert (result, 8'he0);
+
+      #2 op_sel = 5;
+
+      A = 8'hf0;
+      B = 8'h00;
+      C = 1;
+
+      #2 `assert (result, 8'he1);
+      `assert (r_c, 1);
+
+      #2 C = 0;
+
+      #2 `assert (result, 8'he0);
+
+      #2 B = 1;
+      C = 0;
+
+      #2 `assert (result, 8'h78);
+
+      #2 A = 8'hf1;
+      C = 1;
+
+      #2 `assert (result, 8'hf8);
+      `assert (r_c, 1);
+
+      #2 op_sel = 6;
+
+      #500 $finish;
+   end
+
+endmodule