Skip NOP.

src/sap1.v

@@ -102,6 +102,7 @@ endmodule  // Adder and subtractor.
 //     end
 // endmodule // Controller-Sequencer.
 
+/*
 // Version 2: Microprogramming.
 module ctrl_seq (output[11:0] cb, output hlt, input clk,clr, input[3:0] i);
     // Instructions
@@ -164,6 +165,74 @@ module ctrl_seq (output[11:0] cb, output hlt, input clk,clr, input[3:0] i);
         cb = ctrl[counter];
     end
 endmodule // Controller-Sequencer.
+*/
+
+// Version 3: Skip nop.
+module ctrl_seq (output[11:0] cb, output hlt, input clk,clr, input[3:0] i);
+    // Instructions
+    parameter LDA = 4'b0000;
+    parameter ADD = 4'b0001;
+    parameter SUB = 4'b0010;
+    parameter OUT = 4'b1110;
+    parameter HLT = 4'b1111;
+
+    reg[3:0] addr[0:15];   // Address ROM.
+    reg[11:0] ctrl[0:15];  // Control ROM.
+    reg[5:0] sc;           // State counter.
+    reg[3:0] counter;      // Counter.
+
+    assign hlt = i == HLT;
+    assign cb = ctrl[counter];
+
+    wire nop = cb == 12'h000;
+
+    always @ (negedge clk or posedge clr or posedge nop) begin
+        // Initialize address ROM.
+        addr[LDA] = 4'b0011;
+        addr[ADD] = 4'b0110;
+        addr[SUB] = 4'b1001;
+        addr[OUT] = 4'b1100;
+
+        // Initialize control ROM.
+        ctrl[0] = 12'h600;  // 提取
+        ctrl[1] = 12'h800;
+        ctrl[2] = 12'h180;
+        ctrl[3] = 12'h240;  // LDA
+        ctrl[4] = 12'h120;
+        ctrl[5] = 12'h000;  // NOP
+        ctrl[6] = 12'h240;  // ADD
+        ctrl[7] = 12'h102;
+        ctrl[8] = 12'h024;
+        ctrl[9] = 12'h240;  // SUB
+        ctrl[10] = 12'h102;
+        ctrl[11] = 12'h02c;
+        ctrl[12] = 12'h011;  // OUT
+        ctrl[13] = 12'h000;  // NOP
+        ctrl[14] = 12'h000;  // NOP
+
+        // State counter.
+        if (clr | nop) begin
+            sc = 6'b0;
+        end
+
+        if (!clk) begin
+            if(sc[2])
+                counter = addr[i];  // Load address in T3.
+            else
+                counter = counter + 1;
+
+            sc = sc << 1;
+            if (sc == 0) begin
+                sc = 6'b1;
+            end
+        end
+
+        if (clr | sc[0] | nop) begin
+            counter = 4'b0;
+        end
+    end
+endmodule // Controller-Sequencer.
+
 
 // control bus:
 // 11 10 9  8  7  6  5  4  3  2  1  0