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module alu_stage (
input clk,
input en,
input [15:0] pc_in,
input [34:0] control_signals_in,
input [15:0] imm_in,
// register file
output [2:0] rf_regA,
output [2:0] rf_regB,
output [2:0] rf_regDest,
output [15:0] rf_dataIn,
output rf_we,
output rf_hb,
output rf_lb,
input [15:0] rf_dataA,
input [15:0] rf_dataB,
// memory interface
input [15:0] memData_in, // read in from memory
output reg [15:0] memData_out, // to write out to memory
// setting PC
output setPC,
output [15:0] setPCValue,
output reg [34:0] control_signals_out,
output reg [15:0] imm_out,
output reg [15:0] pc_out,
output [1:0] dbg_statusreg
);
reg [1:0] statusReg;
// decode signals
wire [3:0] aluOp_in;
wire [2:0] aluReg1_in;
wire [2:0] aluReg2_in;
wire [1:0] aluOpSource1_in;
wire [1:0] aluOpSource2_in;
wire aluDest_in;
wire [1:0] aluCarrySource;
wire aluCarry_in;
wire [2:0] regDest_in;
wire regSetH_in;
wire regSetL_in;
wire [2:0] regAddr_in;
wire memReadB_in;
wire memReadW_in;
wire memWriteB_in;
wire memWriteW_in;
wire [5:0] setRegCond_in;
ctrl_decode ctrl_decode_inst (
.control_signals(control_signals_in),
.aluOp(aluOp_in),
.aluReg1(aluReg1_in),
.aluReg2(aluReg2_in),
.aluOpSource1(aluOpSource1_in), // ALU first operand: 0 = reg, 1 = memory read, 2 = imm8, 3 = PC
.aluOpSource2(aluOpSource2_in), // ALU second operand: 0 = reg, 1 = ???, 2 = PC, 3 = ???
.aluDest(aluDest_in), // 0 = reg, 1 = PC
.aluCarrySource(aluCarrySource), // ALU carry input source: 0 = zero, 1 = one, 2 = carry flag, 3 = inverted carry flag
.regDest(regDest_in),
.regSetH(regSetH_in),
.regSetL(regSetL_in),
.regAddr(regAddr_in),
.memReadB(memReadB_in),
.memReadW(memReadW_in),
.memWriteB(memWriteB_in),
.memWriteW(memWriteW_in),
.setRegCond(setRegCond_in) // {should set when condition is true, Z doesn't matter, S doesn't matter, Z must be this, S must be this}
);
wire [15:0] aluSrc1;
assign aluSrc1 =
aluOpSource1_in == 2'h0 ? rf_dataA :
aluOpSource1_in == 2'h1 ? memData_in :
aluOpSource1_in == 2'h2 ? {imm_in} : pc_in;
wire [15:0] aluSrc2;
assign aluSrc2 =
aluOpSource1_in == 2'h0 ? rf_dataB : pc_in;
assign aluCarry_in = aluCarrySource[0] ^ (aluCarrySource[1] & statusReg[0]);
wire [15:0] aluResult;
wire aluZero, aluCarry;
alu alu_inst (
.op(aluOp_in),
.x(aluSrc1),
.y(aluSrc2),
.carry_in(aluCarry_in),
.result(aluResult),
.zero(aluZero),
.carry(aluCarry)
);
wire setRegZCond, setRegCCond, setSomeReg;
assign setRegZCond = setRegCond_in[4] | (setRegCond_in[3] == statusReg[1]);
assign setRegCCond = setRegCond_in[1] | (setRegCond_in[0] == statusReg[0]);
assign setSomeReg =
en &
setRegCond_in[5] &
(
setRegCond_in[2] ?
(setRegZCond & setRegCCond) :
(setRegZCond | setRegCCond)
);
assign rf_regA = aluReg1_in;
assign rf_regB = aluReg2_in;
assign rf_we = setSomeReg & !aluDest_in;
assign rf_hb = regSetH_in;
assign rf_lb = regSetL_in;
assign rf_dataIn = aluResult;
assign rf_regDest = regDest_in;
assign setPC = setSomeReg & aluDest_in;
assign setPCValue = aluResult;
always @(posedge clk) begin
if(en) begin
control_signals_out <= control_signals_in;
imm_out <= imm_in;
memData_out <= aluResult;
pc_out <= pc_in;
statusReg <= {aluZero, aluCarry}; // not quite right; should only happen for a few instructions
end
end
assign dbg_statusreg = statusReg;
endmodule
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