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// Instruction decoder of Nandgame
// corresponds to levels
// - control selector
// - control unit
`timescale 1us/1us
`include "alu.sv"
`include "cond_check.sv"
module instruction_decode #(
parameter DATA_WIDTH = 16
) (
input [15:0] instruction,
input [(DATA_WIDTH-1):0] A_i,
input [(DATA_WIDTH-1):0] D_i,
input [(DATA_WIDTH-1):0] pA_i,
output [(DATA_WIDTH-1):0] RES,
output do_jump,
output dst_a,
output dst_d,
output dst_pa
);
wire is_immediate;
// bit 15 set = ALU instruction
// bit 15 unset = immediate
assign is_immediate = !instruction[15];
assign dst_a = is_immediate || instruction[5];
assign dst_d = !is_immediate && instruction[4];
assign dst_pa = !is_immediate && instruction[3];
wire use_pointer_a_for_alu;
wire [(DATA_WIDTH-1):0] alu_y;
assign use_pointer_a_for_alu = instruction[12];
assign alu_y = use_pointer_a_for_alu ? pA_i : A_i;
wire [(DATA_WIDTH-1):0] alu_res;
alu #(
.DATA_WIDTH(DATA_WIDTH)
) my_alu (
.X(D_i),
.Y(alu_y),
.u(instruction[10]),
.opcode(instruction[9:8]),
.zx(instruction[7]),
.sw(instruction[6]),
.RES(alu_res)
);
wire result_jump;
cond_check #(
.DATA_WIDTH(DATA_WIDTH)
) my_cond (
.X(alu_res),
.ltz(instruction[2]),
.eqz(instruction[1]),
.gtz(instruction[0]),
.res(result_jump)
);
assign do_jump = is_immediate ? 0 : result_jump;
assign RES = is_immediate ? instruction : alu_res;
endmodule
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