add ability to make non-aligned loads/stores and loads/stores of 1 or 2 bytes together with test bench

1 files changed, 25 insertions, 12 deletions

diff --git a/design/stack_machine.v b/design/stack_machine.v
index b6c2706..54eae5e 100644
--- a/design/stack_machine.v
+++ b/design/stack_machine.v
@@ -22,7 +22,7 @@ module stack_machine_new
    output reg [20:0] D_ADR_O,
    input wire [31:0] D_DAT_I,
    output reg [31:0] D_DAT_O,
-   output reg [3:0]  D_SEL_O, /* We'll start using it soon */
+   output reg [3:0]  D_SEL_O,
    output reg 	     D_STB_O,
    output reg 	     D_CYC_O,
    output reg 	     D_WE_O,
@@ -37,8 +37,6 @@ module stack_machine_new
       if (CLK_I || !CLK_I) begin /* avoiding "found no sensitivities" warning */
 	 I_DAT_O = 16'bx;
 	 I_WE_O = 1'b0;
-
-	 D_SEL_O = 4'hF; /* This one is temporary */
       end
    end
 
@@ -161,16 +159,25 @@ module stack_machine_new
    wire 	      word_operation;
    wire 	      dword_operation;
    wire 	      qword_operation; /* We won't implement these in hw */
+   wire [3:0] 	      instruction_select_mask;
 
    assign byte_operation  = instruction[9:8] == 2'b00;
    assign word_operation  = instruction[9:8] == 2'b01;
    assign dword_operation = instruction[9:8] == 2'b10;
    assign qword_operation = instruction[9:8] == 2'b11;
+   assign instruction_select_mask = byte_operation ? 4'b0001 :
+				    word_operation ? 4'b0011 :
+				    4'b1111;
 
    /* Flag mainly meant for load instructions, but not exclusively */
    wire 	      sign_extend;
    assign sign_extend = instruction[7];
 
+   wire 	      loaded_value_sign;
+   assign loaded_value_sign = !sign_extend ? 0 :
+			      byte_operation ? D_DAT_I[7] :
+			      word_operation ? D_DAT_I[15] : 1'bx;
+
    /* Instructions other than load and store go here */
 
    /* Instructions, that do not change stack size */
@@ -382,14 +389,14 @@ module stack_machine_new
 		 if (load) begin
 		    D_ADR_O <= addr_to_use;
 		    D_DAT_O <= 32'bx;
-		    /* D_SEL_O <= ????; */ /* We'll later set this one */
+		    D_SEL_O <= instruction_select_mask;
 		    D_STB_O <= 1;
 		    D_CYC_O <= 1;
 		    D_WE_O <= 0;
 		 end else if (store) begin
 		    D_ADR_O <= addr_to_use;
 		    D_DAT_O <= r1;
-		    /* D_SEL_O <= ????; */ /* We'll later set this one */
+		    D_SEL_O <= instruction_select_mask;
 		    D_STB_O <= 1;
 		    D_CYC_O <= 1;
 		    D_WE_O <= 1;
@@ -397,7 +404,7 @@ module stack_machine_new
 		    `SET_SP(sp + 4);
 		    D_ADR_O <= sp;
 		    D_DAT_O <= 32'bx;
-		    /* D_SEL_O <= 4'hF; */
+		    D_SEL_O <= 4'b1111;
 		    D_STB_O <= 1;
 		    D_CYC_O <= 1;
 		    D_WE_O <= 0;
@@ -405,7 +412,7 @@ module stack_machine_new
 		    `SET_SP(sp - 4);
 		    D_ADR_O <= sp - 4;
 		    D_DAT_O <= r0;
-		    /* D_SEL_O <= 4'hF; */
+		    D_SEL_O <= 4'b1111;
 		    D_STB_O <= 1;
 		    D_CYC_O <= 1;
 		    D_WE_O <= 1;
@@ -433,21 +440,21 @@ module stack_machine_new
 		       `SET_SP(sp + 4);
 		       D_ADR_O <= sp;
 		       D_DAT_O <= 32'bx;
-		       /* D_SEL_O <= 4'hF; */
+		       D_SEL_O <= 4'b1111;
 		       D_STB_O <= 1;
 		       D_WE_O <= 0;
 		    end else if (stack_grows) begin
 		       `SET_SP(sp - 4);
 		       D_ADR_O <= sp - 4;
 		       D_DAT_O <= stack_put_value;
-		       /* D_SEL_O <= 4'hF; */
+		       D_SEL_O <= 4'b1111;
 		       D_STB_O <= 1;
 		       D_WE_O <= 1;
 		    end
 		 end else begin // if (load_store_unrequested ||...
 		    D_ADR_O <= 21'bx;
 		    D_DAT_O <= 32'bx;
-		    /* D_SEL_O <= 4'bx; */
+		    D_SEL_O <= 4'bx;
 		    D_STB_O <= 0;
 		    D_WE_O <= 0;
 		 end // else: !if(load_store_unrequested ||...
@@ -475,8 +482,14 @@ module stack_machine_new
 	      if (stack_grows && first_execution_tick)
 		r0 <= r1;
 
-	      if (load && load_store_uncompleted)
-		r1 <= D_DAT_I;
+	      if (load && load_store_uncompleted) begin
+		 if (byte_operation)
+		   r1 <= {{24{loaded_value_sign}}, D_DAT_I[7:0]};
+		 else if (word_operation)
+		   r1 <= {{16{loaded_value_sign}}, D_DAT_I[15:0]};
+		 else
+		   r1 <= D_DAT_I;
+	      end
 
 	      if (!first_execution_tick && use_im)
 		im <= 32'bx;