`include "defines.vh"
module decode_unit #(
		parameter  INSTR_WIDTH  = 16,   // instructions are 16 bits in width
		parameter  R_ADDR_WIDTH = 5

	)(
		input  wire  [INSTR_WIDTH-1:0]   instruction,
		output reg   [`OPCODE_COUNT-1:0] opcode_type,
		output wire  [`GROUP_COUNT-1:0]  opcode_group,
		output reg   [R_ADDR_WIDTH-1:0]  opcode_rd,
		output reg   [R_ADDR_WIDTH-1:0]  opcode_rr,
		output reg               [11:0]  opcode_imd,
		output reg                [2:0]  opcode_bit
	);

/*Fiindca register file-ul procesorului nostru (ATtiny20)
are doar 16 registre, putem ignora bitii Rr si Rd de pe pozitiile 9 si 8
(Atmel garanteaza ca, din motive de compatibilitate, vor fi mereu setati
pe 1, sau, echivalent, vor fi folosite numai registrele R16 ? R31).
Deci opcode = 000111rdxxxxxxxx devifne 00011111xxxxxxxx. (Btw, that's ADD)
*/

	always @* begin
		  casez (instruction)
			16'b0000_11??_????_????: begin
				opcode_type = `TYPE_ADD;
				opcode_rd   = instruction[8:4];
				opcode_rr   = {instruction[9], instruction[3:0]};
			end
			16'b0001_11??_????_????: begin
				opcode_type = `TYPE_ADC;
				opcode_rd   = instruction[8:4];
				opcode_rr   = {instruction[9], instruction[3:0]};
			end
			16'b0010_00??_????_????: begin
				opcode_type = `TYPE_AND;
				opcode_rd   = instruction[8:4];
				opcode_rr   = {instruction[9], instruction[3:0]};
			end
				16'b0010_01??_????_????: begin
				opcode_type = `TYPE_EOR;
				opcode_rd   = instruction[8:4];
				opcode_rr   = {instruction[9], instruction[3:0]};
			end
			/* TODO 5: LD_Y */
			16'b1000_000?_????_1000: begin
				opcode_type = `TYPE_LD_Y;
				opcode_rd   = instruction[8:4];
				opcode_rr   = {R_ADDR_WIDTH{1'bx}};
			end
			/* TODO 3: LDI */
			16'b1110_????_????_????: begin
				opcode_type = `TYPE_LDI;
				opcode_rd   = instruction[7:4];
				opcode_imd   = {instruction[11:8], instruction[3:0]};
			end
			/* TODO 6,7: instructions */
			16'b1010_0???_????_????: begin
				opcode_type = `TYPE_LDS;
				opcode_rd   = instruction[7:4];
				opcode_imd   = {instruction[10:8], instruction[3:0]};
			end
			16'b1001_010?_????_0001: begin
				opcode_type = `TYPE_NEG;
				opcode_rd   = instruction[8:4];
				opcode_rr   = {R_ADDR_WIDTH{1'bx}};
			end
			16'b0000_0000_0000_0000: begin
				opcode_type = `TYPE_NOP;
				opcode_rd   = {R_ADDR_WIDTH{1'bx}};
				opcode_rr   = {R_ADDR_WIDTH{1'bx}};
			end
			16'b0010_10??_????_????: begin
				opcode_type = `TYPE_OR;
				opcode_rd   = instruction[8:4];
				opcode_rr   = {instruction[9], instruction[3:0]};
			end
			16'b0001_10??_????_????: begin
				opcode_type = `TYPE_SUB;
				opcode_rd   = instruction[8:4];
				opcode_rr   = {instruction[9], instruction[3:0]};
			end
			/*TODO 4: STS */
				/* TODO : De codificat instructiunile din laborator. */
			16'b1010_1???_????_????: begin
				opcode_type = `TYPE_STS;
				opcode_rr   = instruction[7:4];
				opcode_imd   = {instruction[10:8], instruction[3:0]};
			end
			16'b0010_11??_????_????: begin
				opcode_type = `TYPE_MOV;
				opcode_rd   = instruction[8:4];
				opcode_rr   = {instruction[9], instruction[3:0]};
			end

				default: begin
					opcode_type = `TYPE_UNKNOWN;
					opcode_rd   = {R_ADDR_WIDTH{1'bx}};
					opcode_rr   = {R_ADDR_WIDTH{1'bx}};
				end
		/*TODO : completati cu opcodes ale voastre.
		  Where can I find such opcodes? Make them up or read the lab and see
		  they're at http://www.atmel.com/images/Atmel-0856-AVR-Instruction-Set-Manual.pdf  */
		  /* Cand gasiti o instructiune de UAL, setati opcode_type la valoarea corecta */
		  /*  instruction seamana cu un ADD? -> opcode_type = `TYPE_ADD; */
		  endcase
	end

	assign opcode_group[`GROUP_ALU_ONE_OP] =
		(opcode_type == `TYPE_NEG);
	assign opcode_group[`GROUP_ALU_TWO_OP] =
		(opcode_type == `TYPE_ADD) ||
		(opcode_type == `TYPE_ADC) ||
		(opcode_type == `TYPE_SUB) ||
		(opcode_type == `TYPE_AND) ||
		(opcode_type == `TYPE_EOR) ||
		(opcode_type == `TYPE_OR);
	assign opcode_group[`GROUP_ALU] =
		opcode_group[`GROUP_ALU_ONE_OP] ||
		opcode_group[`GROUP_ALU_TWO_OP];

	assign opcode_group[`GROUP_LOAD_DIRECT] =
		(opcode_type == `TYPE_LDI) ||
		(opcode_type == `TYPE_LDS);
	assign opcode_group[`GROUP_LOAD_INDIRECT] =
		(opcode_type == `TYPE_LD_Y);

	assign opcode_group[`GROUP_STORE_DIRECT] =
		(opcode_type == `TYPE_STS);
	assign opcode_group[`GROUP_STORE_INDIRECT] =
		0;

	assign opcode_group[`GROUP_REGISTER] =
		/* TODO 3: LDI */
		(opcode_type == `TYPE_MOV);

	assign opcode_group[`GROUP_LOAD] =
		opcode_group[`GROUP_LOAD_DIRECT] ||
		opcode_group[`GROUP_LOAD_INDIRECT];
	assign opcode_group[`GROUP_STORE] =
		opcode_group[`GROUP_STORE_DIRECT] ||
		opcode_group[`GROUP_STORE_INDIRECT];
	assign opcode_group[`GROUP_MEMORY] =
		(opcode_group[`GROUP_LOAD] ||
		 opcode_group[`GROUP_STORE]);
endmodule