Add ZP address mode

src/cpu.verilog

@@ -19,7 +19,7 @@ module cpu
     localparam STATE_FETCH = 0;
     localparam STATE_EXECUTE = 1;
     localparam STATE_WRITE = 2;
-    localparam STATE_FETCH_DATA_1 = 3;
+    localparam STATE_EXECUTE_ZP = 3;
     localparam STATE_FETCH_DATA_2 = 4;
     localparam STATE_EXECUTE_DATA_2 = 5;
     localparam STATE_BRANCH = 7;
@@ -61,6 +61,8 @@ localparam
     logic [7:0] mem_data_wr;
     logic [2:0] mem_sel;
     logic [7:0] mem_aux_addr;
+    logic [7:0] mem_aux_addr_lo;
+    logic [7:0] mem_aux_addr_hi;
 
     logic [7:0]  alu_op_1;
     logic [7:0]  alu_op_2;
@@ -127,13 +129,27 @@ dmux dmuxi(
            .i_x(X),
            .i_y(Y),
            .i_sp(S),
-           .i_aux({mem_data, mem_aux_addr}),
+           .i_aux({mem_aux_addr_hi, mem_aux_addr_lo}),
            .o_mux(mem_addr));
 
 initial state = STATE_FETCH;
 initial PC = 0;
 initial mem_sel = 0;
 
+always_comb
+  begin
+      mem_aux_addr_lo = mem_aux_addr;
+      mem_aux_addr_hi = 0;
+      if (address_code == ADDR_MODE_ABSOLUTE)
+        begin
+            mem_aux_addr_hi = mem_data;
+        end
+      else if (address_code == ADDR_MODE_ZP)
+        begin
+            mem_aux_addr_lo = mem_data;
+        end
+  end
+
 always_comb
   begin
       alu_op_1 = 0;
@@ -147,7 +163,8 @@ always_comb
             alu_op_c = 1'b1;
             alu_op_sel = OP_SUB;
         end
-      if (address_code == ADDR_MODE_ABSOLUTE)
+      else if (address_code == ADDR_MODE_ABSOLUTE ||
+               address_code == ADDR_MODE_ZP)
         begin
             if (decoded_instr == I_EOR)
               begin
@@ -156,6 +173,20 @@ always_comb
                   alu_op_c = 0;
                   alu_op_sel = OP_EOR;
               end
+            else if (decoded_instr == I_AND)
+              begin
+                  alu_op_1 = A;
+                  alu_op_2 = mem_data;
+                  alu_op_c = 0;
+                  alu_op_sel = OP_AND;
+              end
+            else if (decoded_instr == I_ORA)
+              begin
+                  alu_op_1 = A;
+                  alu_op_2 = mem_data;
+                  alu_op_c = 0;
+                  alu_op_sel = OP_OR;
+              end
         end
   end
 
@@ -217,6 +248,12 @@ always @(posedge clk)
                     PC <= PC + 1;
                 end
           end
+        else if (address_code == ADDR_MODE_ZP)
+          begin
+              mem_sel <= DMUX_AUX;
+              state <= STATE_EXECUTE_ZP;
+              PC <= PC + 1;
+          end
         else if (address_code == ADDR_MODE_IMPLIED)
           begin
               if (decoded_instr == I_DEX)
@@ -240,6 +277,14 @@ always @(posedge clk)
                 end
           end
     end
+  else if (state == STATE_EXECUTE_ZP)
+    begin
+        mem_aux_addr <= mem_data;
+        mem_sel <= DMUX_PC;
+        pending_a_read <= READ_SOURCE_ALU;
+
+        state <= STATE_FETCH;
+    end
   else if (state == STATE_BRANCH)
     begin
         if (pending_rel_branch)
@@ -266,7 +311,9 @@ always @(posedge clk)
               begin
                   mem_sel <= DMUX_PC;
                   state <= STATE_FETCH;
-                  if (decoded_instr == I_EOR)
+                  if (decoded_instr == I_EOR ||
+                      decoded_instr == I_AND ||
+                      decoded_instr == I_ORA)
                     begin
                         tmp <= mem_data;
                         pending_a_read <= READ_SOURCE_ALU;
@@ -293,6 +340,14 @@ always_comb
                     end
               end
         end
+      else if (state == STATE_EXECUTE_ZP)
+        begin
+            if(decoded_instr == I_STA)
+              begin
+                  mem_data_wr = A;
+                  mem_wr = 1'b1;
+              end
+        end
   end
 
 `ifdef FORMAL
@@ -398,16 +453,25 @@ always @(posedge clk)
   if (f2_past_valid &&
       state == STATE_EXECUTE &&
       $past(state) == STATE_FETCH &&
-      $past(state, 2) == STATE_EXECUTE_DATA_2)
-    if ($past(address_code, 2) == ADDR_MODE_ABSOLUTE)
+      ($past(state, 2) == STATE_EXECUTE_DATA_2 ||
+       $past(state, 2) == STATE_EXECUTE_ZP))
     begin
         if ($past(decoded_instr, 2) == I_EOR)
-            assert(A == $past(A, 2) ^ $past(mem_data));
+          assert(A == ($past(A) ^ $past(mem_data)));
+        else if ($past(decoded_instr, 2) == I_AND)
+          assert(A == ($past(A) & $past(mem_data)));
+        else if ($past(decoded_instr, 2) == I_ORA)
+          assert(A == ($past(A) | $past(mem_data)));
         else
           assume(0);
 
         assert($past(mem_wr, 2) == 1'b0);
+
+        if ($past(address_code, 2) == ADDR_MODE_ABSOLUTE)
           assert($past(f_abs_address, 2) == $past(mem_addr_eff, 2));
+        else
+          assert($past(mem_data, 2) == $past(mem_addr_eff, 2));
+
         assert(P[P_Z] == (A == 0));
         assert(P[P_N] == (A[7] == 1));
         assert(P[P_C] == $past(P[P_C], 3));
@@ -421,7 +485,10 @@ always @(posedge clk)
 
         if (f3_past_valid)
           begin
+              if ($past(address_code, 2) == ADDR_MODE_ABSOLUTE)
                 assert($past(PC, 2) == $past(PC, 5) + 16'd3);
+              else if ($past(address_code, 2) == ADDR_MODE_ZP)
+                assert($past(PC, 2) == $past(PC, 4) + 16'd2);
           end
     end
 

src/mio.verilog

@@ -25,7 +25,13 @@ module mio(clk, i_data, i_addr, i_wr, o_data, o_led);
 initial o_led = 6'h3f;
 
 `ifndef FORMAL
-initial $readmemh("foo.hex", memory);
+initial $readmemh("foo.hex", memory, 0, 32);
+initial begin
+    for (integer i = 32; i < 256; i++)
+      begin
+          memory[i] = 0;
+      end
+    end
 `else
     reg f_init_done = 0;
 always @(posedge clk)