ELEC40006-P1-CW/DECODE.v

module DECODE
(
	input [15:0] instr,
	input FETCH,
	input EXEC1,
	input EXEC2,
	input COND_result,
	output R0_count,
	output R0_en,
	output R1_en,
	output R2_en,
	output R3_en,
	output R4_en,
	output R5_en,
	output R6_en,
	output R7_en,
	output [2:0] s1,
	output [2:0] s2,
	output [2:0] s3,
	output s4,
	output RAMd_wren,
	output RAMd_en,
	output RAMi_en,
	output ALU_en,
	output E2,
	output stack_en,
	output stack_rst,
	output stack_rw,
	output s5
);

	wire msb = instr[15];					//MSB of the instruction word
	wire ls = instr[14];						//LDA or STA bit
	wire [2:0] Rls = instr[13:11];		//Register in the LDA/STA operation
	wire [10:0] addr = instr[10:0];		//Memory address in the LDA/STA operation
	wire [5:0] op = instr[14:9];			//Opcode in regular instructions
	wire [2:0] Rd = instr[8:6];			//Destination register in command
	wire [2:0] Rs1 = instr[5:3];			//Source register 1 in command
	wire [2:0] Rs2 = instr[2:0];			//Source register 2 in command
	
	//Different opcodes (refer to documentation):
	wire LDA =  msb & ~ls;
	wire STA =  msb &  ls;
	wire JMP = ~msb & ~op[5] & ~op[4] & ~op[3] & ~op[2] & ~op[1] & ~op[0];
	wire JMA = ~msb & ~op[5] & ~op[4] & ~op[3] & ~op[2] & ~op[1] &  op[0];
	wire JCX = ~msb & ((~op[5] & ~op[4] & ~op[3] & op[2]) | (~op[5] & ~op[4] & op[3] & ~op[2]));
	wire MUL = ~msb & ~op[5] &  op[4] &  op[3] &  op[2] & ~op[1] & ~op[0];
	wire MLA = ~msb & ~op[5] &  op[4] &  op[3] &  op[2] & ~op[1] &  op[0];
	wire MLS = ~msb & ~op[5] &  op[4] &  op[3] &  op[2] &  op[1] & ~op[0];
	wire PSH = ~msb &  op[5] & ~op[4] &  op[3] & ~op[2] & ~op[1] & ~op[0];
	wire POP = ~msb &  op[5] & ~op[4] &  op[3] & ~op[2] & ~op[1] &  op[0];
	wire LDR = ~msb &  op[5] & ~op[4] &  op[3] & ~op[2] &  op[1] & ~op[0];
	wire STR = ~msb &  op[5] & ~op[4] &  op[3] & ~op[2] &  op[1] &  op[0];
	wire CLL = ~msb &  op[5] & ~op[4] & ~op[3] &  op[2] &  op[1] & ~op[0];
	wire RTN = ~msb &  op[5] & ~op[4] & ~op[3] &  op[2] &  op[1] &  op[0];
	wire NOP = ~msb &  op[5] &  op[4] &  op[3] &  op[2] &  op[1] & ~op[0];
	wire STP = ~msb &  op[5] &  op[4] &  op[3] &  op[2] &  op[1] &  op[0];
	
	assign R0_count = EXEC1 & (~(JMP | JMA | (JCX & COND_result) | STP | CLL | RTN));
	assign R0_en = (EXEC1 & (~(STA | NOP | STP | LDA | PSH | LDR | CLL | RTN) & ~Rd[2] & ~Rd[1] & ~Rd[0] | JMP | (JCX & COND_result) | JMA)) | (EXEC2 & LDA & ~Rls[2] & ~Rls[1] & ~Rls[0]) | (EXEC2 & (MUL | MLA | MLS | POP | STR | LDR) & ~Rd[2] & ~Rd[1] & ~Rd[0]) | (EXEC2 & RTN) | (EXEC1 & CLL);
	assign R1_en = (EXEC1 & ~(JMP | JMA | JCX | STA | LDA | MUL | MLA | MLS | NOP | STP | POP | PSH | LDR | CLL | RTN) & ~Rd[2] & ~Rd[1] &  Rd[0]) | (EXEC2 & LDA & ~Rls[2] & ~Rls[1] &  Rls[0]) | (EXEC2 & (MUL | MLA | MLS | POP | LDR) & ~Rd[2] & ~Rd[1] &  Rd[0]);
	assign R2_en = (EXEC1 & ~(JMP | JMA | JCX | STA | LDA | MUL | MLA | MLS | NOP | STP | POP | PSH | LDR | CLL | RTN) & ~Rd[2] &  Rd[1] & ~Rd[0]) | (EXEC2 & LDA & ~Rls[2] &  Rls[1] & ~Rls[0]) | (EXEC2 & (MUL | MLA | MLS | POP | LDR) & ~Rd[2] &  Rd[1] & ~Rd[0]);
	assign R3_en = (EXEC1 & ~(JMP | JMA | JCX | STA | LDA | MUL | MLA | MLS | NOP | STP | POP | PSH | LDR | CLL | RTN) & ~Rd[2] &  Rd[1] &  Rd[0]) | (EXEC2 & LDA & ~Rls[2] &  Rls[1] &  Rls[0]) | (EXEC2 & (MUL | MLA | MLS | POP | LDR) & ~Rd[2] &  Rd[1] &  Rd[0]);
	assign R4_en = (EXEC1 & ~(JMP | JMA | JCX | STA | LDA | MUL | MLA | MLS | NOP | STP | POP | PSH | LDR | CLL | RTN) &  Rd[2] & ~Rd[1] & ~Rd[0]) | (EXEC2 & LDA &  Rls[2] & ~Rls[1] & ~Rls[0]) | (EXEC2 & (MUL | MLA | MLS | POP | LDR) &  Rd[2] & ~Rd[1] & ~Rd[0]);
	assign R5_en = (EXEC1 & ~(JMP | JMA | JCX | STA | LDA | MUL | MLA | MLS | NOP | STP | POP | PSH | LDR | CLL | RTN) &  Rd[2] & ~Rd[1] &  Rd[0]) | (EXEC2 & LDA &  Rls[2] & ~Rls[1] &  Rls[0]) | (EXEC2 & (MUL | MLA | MLS | POP | LDR) &  Rd[2] & ~Rd[1] &  Rd[0]);
	assign R6_en = (EXEC1 & ~(JMP | JMA | JCX | STA | LDA | MUL | MLA | MLS | NOP | STP | POP | PSH | LDR | CLL | RTN) &  Rd[2] &  Rd[1] & ~Rd[0]) | (EXEC2 & LDA &  Rls[2] &  Rls[1] & ~Rls[0]) | (EXEC2 & (MUL | MLA | MLS | POP | LDR) &  Rd[2] &  Rd[1] & ~Rd[0]);
	assign R7_en = (EXEC1 & ~(JMP | JMA | JCX | STA | LDA | MUL | MLA | MLS | NOP | STP | POP | PSH | LDR | CLL | RTN) &  Rd[2] &  Rd[1] &  Rd[0]) | (EXEC2 & LDA &  Rls[2] &  Rls[1] &  Rls[0]) | (EXEC2 & (MUL | MLA | MLS | POP | LDR) &  Rd[2] &  Rd[1] &  Rd[0]);
	assign s1[2] = (~(JMP | JMA | STA | LDA | NOP | STP | POP | CLL | RTN) & Rs1[2]) | (STA & Rls[2]);
	assign s1[1] = (~(JMP | JMA | STA | LDA | NOP | STP | POP | CLL | RTN) & Rs1[1]) | (STA & Rls[1]);
	assign s1[0] = (~(JMP | JMA | STA | LDA | NOP | STP | POP | CLL | RTN) & Rs1[0]) | (STA & Rls[0]);
	assign s2[2] = (~(JMP | JMA | STA | LDA | NOP | STP | POP | PSH | LDR | STR | CLL | RTN) & Rs2[2]);
	assign s2[1] = (~(JMP | JMA | STA | LDA | NOP | STP | POP | PSH | LDR | STR | CLL | RTN) & Rs2[1]);
	assign s2[0] = (~(JMP | JMA | STA | LDA | NOP | STP | POP | PSH | LDR | STR | CLL | RTN) & Rs2[0]);
	assign s3[2] = (~(STA | LDA | NOP | STP | PSH | POP | RTN) & Rd[2]);
	assign s3[1] = (~(STA | LDA | NOP | STP | PSH | POP | RTN) & Rd[1]);
	assign s3[0] = (~(STA | LDA | NOP | STP | PSH | POP | RTN) & Rd[0]);
	assign s4 = ~(LDA | LDR);
	assign RAMd_wren = EXEC1 & (STA | STR);
	assign RAMd_en = EXEC1 & (STA | LDA | STR | LDR);
	assign RAMi_en = FETCH;
	assign ALU_en = LDA | STA;
	assign E2 = EXEC1 & (LDA | MUL | MLA | MLS | POP | LDR | RTN);
	assign stack_en = (EXEC1 & (PSH | CLL | RTN | POP));
	assign stack_rst = STP;
	assign stack_rw = EXEC1 & (PSH | CLL);
	assign s5 = EXEC1 & (STR | LDR);
	
endmodule