Execute: most of an ALU, ARM_Constants: RBC -> RSC

[firearm.git] / Execute.v

diff --git a/Execute.v b/Execute.v
index 5ba0a9a96aea7101a701cc0496893581f9c8e4a1..4865aa359bd262ceabc18a21bcae8e098698fcfe 100644 (file)
--- a/Execute.v
+++ b/Execute.v
@@ -15,7 +15,175 @@ module Execute(
        input carry,
        
        output reg outstall = 0,
-       output reg outbubble = 1
+       output reg outbubble = 1,
+       output reg write_reg = 1'bx,
+       output reg [3:0] write_num = 4'bxxxx,
+       output reg [31:0] write_data = 32'hxxxxxxxx
        );
        
+       reg mult_start;
+       reg [31:0] mult_acc0, mult_in0, mult_in1;
+       wire mult_done;
+       wire [31:0] mult_result;
+       
+       Multiplier multiplier(
+               .clk(clk), .Nrst(Nrst),
+               .start(mult_start), .acc0(mult_acc0), .in0(mult_in0),
+               .in1(mult_in1), .done(mult_done), .result(mult_result));
+endmodule
+
+module Multiplier(
+       input clk,
+       input Nrst,     /* XXX not used yet */
+       
+       input start,
+       input [31:0] acc0,
+       input [31:0] in0,
+       input [31:0] in1,
+       
+       output reg done = 0,
+       output reg [31:0] result);
+       
+       reg [31:0] bitfield;
+       reg [31:0] multiplicand;
+       reg [31:0] acc;
+       
+       always @(posedge clk)
+       begin
+               if (start) begin
+                       bitfield <= in0;
+                       multiplicand <= in1;
+                       acc <= acc0;
+                       done <= 0;
+               end else begin
+                       bitfield <= {2'b00, bitfield[31:2]};
+                       multiplicand <= {multiplicand[29:0], 2'b00};
+                       acc <= acc +
+                               (bitfield[0] ? multiplicand : 0) +
+                               (bitfield[1] ? {multiplicand[30:0], 1'b0} : 0);
+                       if (bitfield == 0) begin
+                               result <= acc;
+                               done <= 1;
+                       end
+               end
+       end
+endmodule
+
+/* XXX is the interface correct? */
+module ALU(
+       input clk,
+       input Nrst,     /* XXX not used yet */
+
+       input [31:0] in0,
+       input [31:0] in1,
+       input [31:0] cpsr,
+       input [3:0] op,
+       input setflags,
+       input shifter_carry,
+
+       output reg [31:0] result,
+       output reg [31:0] cpsr_out,
+       output reg set
+);
+       wire [31:0] res;
+       wire flag_n, flag_z, flag_c, flag_v, setres;
+       wire [32:0] sum, diff, rdiff;
+
+       assign sum = {1'b0, in0} + {1'b0, in1};
+       assign diff = {1'b0, in0} - {1'b0, in1};
+       assign rdiff = {1'b0, in1} + {1'b0, in0};
+
+       /* TODO XXX flag_v not set correctly */
+       always @(*) begin
+               res = 32'hxxxxxxxx;
+               setres = 1'bx;
+               flag_c = cpsr[`CPSR_C];
+               flag_v = cpsr[`CPSR_V];
+               case(op)
+               `ALU_AND: begin
+                       res = in0 & in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               `ALU_EOR: begin
+                       res = in0 ^ in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               `ALU_SUB: begin
+                       {flag_c, res} = diff;
+                       setres = 1'b1;
+               end
+               `ALU_RSB: begin
+                       {flag_c, res} = rdiff;
+                       setres = 1'b1;
+               end
+               `ALU_ADD: begin
+                       {flag_c, res} = sum;
+                       setres = 1'b1;
+               end
+               `ALU_ADC: begin
+                       {flag_c, res} = sum + cpsr[`CPSR_C];
+                       setres = 1'b1;
+               end
+               `ALU_SBC: begin
+                       {flag_c, res} = diff - (~cpsr[`CPSR_C]);
+                       setres = 1'b1;
+               end
+               `ALU_RSC: begin
+                       {flag_c, res} = rdiff - (~cpsr[`CPSR_C]);
+                       setres = 1'b1;
+               end
+               `ALU_TST: begin
+                       res = in0 & in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b0;
+               end
+               `ALU_TEQ: begin
+                       res = in0 ^ in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b0;
+               end
+               `ALU_CMP: begin
+                       {flag_c, res} = diff;
+                       setres = 1'b0;
+               end
+               `ALU_CMN: begin
+                       {flag_c, res} = sum;
+                       setres = 1'b0;
+               end
+               `ALU_ORR: begin
+                       res = in0 | in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               `ALU_MOV: begin
+                       res = in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               `ALU_BIC: begin
+                       res = in0 & (~in1);
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               `ALU_MVN: begin
+                       res = ~in1;
+                       flag_c = shifter_carry;
+                       setres = 1'b1;
+               end
+               endcase
+       end
+
+       always @(*) begin
+               flag_z = (res == 0);
+               flag_n = res[31];
+       end
+
+       always @(posedge clk) begin
+               result <= res;
+               cpsr_out <= setflags ? {flag_n, flag_z, flag_c, flag_v, cpsr[27:0]} : cpsr;
+               set <= setres;
+       end
+
 endmodule