Add DEY instruction

src/cpu.verilog

@@ -78,6 +78,7 @@ localparam
     reg [2:0]    mem_addr_offset;
     logic [1:0]  pending_a_read;
     logic [1:0]  pending_x_read;
+    logic [1:0]  pending_y_read;
     logic        pending_rel_branch;
 
 initial A = 0;
@@ -90,6 +91,7 @@ initial mem_wr = 0;
 assign mem_addr_eff = mem_addr;
 initial pending_a_read = 0;
 initial pending_x_read = 0;
+initial pending_y_read = 0;
 initial pending_rel_branch = 0;
 
 assign o_state[3:0] = state;
@@ -163,7 +165,15 @@ always_comb
             alu_op_c = 1'b1;
             alu_op_sel = OP_SUB;
         end
-      else if (address_code == ADDR_MODE_ABSOLUTE ||
+      else if (decoded_instr == I_DEY)
+        begin
+            alu_op_1 = Y;
+            alu_op_2 = 1'b1;
+            alu_op_c = 1'b1;
+            alu_op_sel = OP_SUB;
+        end
+      else if (address_code == ADDR_MODE_IMMEDIATE ||
+               address_code == ADDR_MODE_ABSOLUTE ||
                address_code == ADDR_MODE_ZP)
         begin
             if (decoded_instr == I_EOR)
@@ -220,6 +230,21 @@ always @(posedge clk)
               P[P_N] <= alu_n;
           end
         pending_x_read <= READ_SOURCE_NONE;
+
+        if (pending_y_read == READ_SOURCE_MEM)
+          begin
+              Y <= mem_data;
+              P[P_Z] <= (mem_data == 0);
+              P[P_N] <= mem_data[7];
+          end
+        else if (pending_y_read == READ_SOURCE_ALU)
+          begin
+              Y <= alu_op_result;
+              P[P_Z] <= alu_z;
+              P[P_N] <= alu_n;
+          end
+        pending_y_read <= READ_SOURCE_NONE;
+
         PC <= PC + 1;
         state <= STATE_EXECUTE;
     end
@@ -236,17 +261,20 @@ always @(posedge clk)
               if (decoded_instr == I_LDX)
                 begin
                     pending_x_read <= READ_SOURCE_MEM;
-
-                    state <= STATE_FETCH;
-                    PC <= PC + 1;
                 end
               else if (decoded_instr == I_LDA)
                 begin
                     pending_a_read <= READ_SOURCE_MEM;
-
-                    state <= STATE_FETCH;
-                    PC <= PC + 1;
                 end
+              else if (decoded_instr == I_EOR ||
+                       decoded_instr == I_AND ||
+                       decoded_instr == I_ORA)
+                begin
+                    pending_a_read <= READ_SOURCE_ALU;
+                end
+
+              state <= STATE_FETCH;
+              PC <= PC + 1;
           end
         else if (address_code == ADDR_MODE_ZP)
           begin
@@ -259,7 +287,11 @@ always @(posedge clk)
               if (decoded_instr == I_DEX)
                 begin
                     pending_x_read <= READ_SOURCE_ALU;
-
+                    state <= STATE_FETCH;
+                end
+              else if (decoded_instr == I_DEY)
+                begin
+                    pending_y_read <= READ_SOURCE_ALU;
                     state <= STATE_FETCH;
                 end
           end
@@ -386,7 +418,7 @@ always @(posedge clk)
   if (f2_past_valid && state == STATE_EXECUTE)
     if ($past(decoded_instr) == I_DEX)
       begin
-          assert(X == $past(X, 2) - 8'd1);
+          assert(X == $past(X, 3) - 8'd1);
           assert($past(PC) == $past(PC, 3) + 16'd1);
           assert(P[P_Z] == (X == 0));
           assert(P[P_N] == (X[7] == 1));
@@ -397,6 +429,21 @@ always @(posedge clk)
           assert($stable(P[P_I]));
       end
 
+always @(posedge clk)
+  if (f2_past_valid && state == STATE_EXECUTE)
+    if ($past(decoded_instr) == I_DEY)
+      begin
+          assert(Y == $past(Y, 3) - 8'd1);
+          assert($past(PC) == $past(PC, 3) + 16'd1);
+          assert(P[P_Z] == (Y == 0));
+          assert(P[P_N] == (Y[7] == 1));
+          assert($stable(P[P_C]));
+          assert($stable(P[P_V]));
+          assert($stable(P[P_B]));
+          assert($stable(P[P_D]));
+          assert($stable(P[P_I]));
+      end
+
 always @(posedge clk)
   if (f2_past_valid && state == STATE_EXECUTE)
     if ($past(decoded_instr) == I_LDX && $past(address_code) == ADDR_MODE_IMMEDIATE)
@@ -450,11 +497,12 @@ always @(posedge clk)
       end
 
 always @(posedge clk)
-  if (f2_past_valid &&
+  if (f4_past_valid &&
       state == STATE_EXECUTE &&
       $past(state) == STATE_FETCH &&
       ($past(state, 2) == STATE_EXECUTE_DATA_2 ||
-       $past(state, 2) == STATE_EXECUTE_ZP))
+       $past(state, 2) == STATE_EXECUTE_ZP ||
+       $past(state, 2) == STATE_EXECUTE))
     begin
         if ($past(decoded_instr, 2) == I_EOR)
           assert(A == ($past(A) ^ $past(mem_data)));
@@ -469,19 +517,19 @@ always @(posedge clk)
 
         if ($past(address_code, 2) == ADDR_MODE_ABSOLUTE)
           assert($past(f_abs_address, 2) == $past(mem_addr_eff, 2));
-        else
+        else if ($past(address_code, 2) == ADDR_MODE_ZP)
           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));
-        assert(P[P_V] == $past(P[P_V], 3));
-        assert(P[P_B] == $past(P[P_B], 3));
-        assert(P[P_D] == $past(P[P_D], 3));
-        assert(P[P_I] == $past(P[P_I], 3));
-        assert(S == $past(S, 3));
-        assert(X == $past(X, 3));
-        assert(Y == $past(Y, 3));
+        assert(P[P_C] == $past(P[P_C], 2));
+        assert(P[P_V] == $past(P[P_V], 2));
+        assert(P[P_B] == $past(P[P_B], 2));
+        assert(P[P_D] == $past(P[P_D], 2));
+        assert(P[P_I] == $past(P[P_I], 2));
+        assert(S == $past(S, 2));
+        assert(X == $past(X, 2));
+        assert(Y == $past(Y, 2));
 
         if (f3_past_valid)
           begin
@@ -489,6 +537,8 @@ always @(posedge clk)
                 assert($past(PC, 2) == $past(PC, 5) + 16'd3);
               else if ($past(address_code, 2) == ADDR_MODE_ZP)
                 assert($past(PC, 2) == $past(PC, 4) + 16'd2);
+              else if ($past(address_code, 2) == ADDR_MODE_IMMEDIATE)
+                assert($past(PC, 1) == $past(PC, 3) + 16'd2);
           end
     end