From d4cad6096651774485723551336bce1d08402b6e Mon Sep 17 00:00:00 2001
From: Nick McKinney <nick@kmonkey.net>
Date: Sun, 18 Dec 2016 16:22:03 -0600
Subject: add simple control unit

---
 control_unit.v | 36 ++++++++++++++++++++++++++++++++++++
 nqcpu.qsf      |  1 +
 nqcpu.v        | 27 ++++++++++++++++++++++-----
 3 files changed, 59 insertions(+), 5 deletions(-)
 create mode 100644 control_unit.v

diff --git a/control_unit.v b/control_unit.v
new file mode 100644
index 0000000..00ebd4f
--- /dev/null
+++ b/control_unit.v
@@ -0,0 +1,36 @@
+module control_unit (
+	input clk,
+	
+	input fetch_ready,
+	
+	output fetch_en,
+	output decode_en,
+	output alu_en,
+	
+	output incr_pc,
+	
+	output [9:0] dbg_state
+);
+
+	reg [9:0] current_state;
+	
+	initial begin
+		current_state = 10'b1;
+	end
+	
+	assign fetch_en = current_state[0];
+	assign decode_en = current_state[1];
+	assign alu_en = current_state[2];
+	
+	assign incr_pc = current_state[1];
+	
+	always @(posedge clk) begin
+		case(current_state)
+			10'b1: if(fetch_ready) current_state <= 10'b10;
+			10'b10: current_state <= 10'b100;
+			10'b100: current_state <= 10'b1;
+		endcase
+	end
+	
+	assign dbg_state = current_state;
+endmodule
diff --git a/nqcpu.qsf b/nqcpu.qsf
index d196471..0550532 100644
--- a/nqcpu.qsf
+++ b/nqcpu.qsf
@@ -64,4 +64,5 @@ set_global_assignment -name PARTITION_NETLIST_TYPE SOURCE -section_id Top
 set_global_assignment -name PARTITION_FITTER_PRESERVATION_LEVEL PLACEMENT_AND_ROUTING -section_id Top
 set_global_assignment -name PARTITION_COLOR 16764057 -section_id Top
 set_global_assignment -name VERILOG_FILE alu_stage.v
+set_global_assignment -name VERILOG_FILE control_unit.v
 set_instance_assignment -name PARTITION_HIERARCHY root_partition -to | -section_id Top
\ No newline at end of file
diff --git a/nqcpu.v b/nqcpu.v
index 7656159..9dac5cf 100644
--- a/nqcpu.v
+++ b/nqcpu.v
@@ -28,7 +28,8 @@ module nqcpu (
 	output [15:0] dbg_r4,
 	output [15:0] dbg_r5,
 	output [15:0] dbg_r6,
-	output [15:0] dbg_r7
+	output [15:0] dbg_r7,
+	output [9:0] dbg_state
 );
 
 	reg [15:0] pc;
@@ -37,12 +38,14 @@ module nqcpu (
 		pc = 16'h0;
 	end
 
+	wire fetch_en, decode_en, alu_en, incr_pc;
+
 	wire fetch_ready;
 	wire [15:0] fetched_instr;
 	wire [15:0] pc_from_fetch;
 	fetch_stage fetch_inst (
 		.clk(clk),
-		.en(1'b1),
+		.en(fetch_en),
 		.addr_in(pc),
 		.ready(fetch_ready),
 		.instr_out(fetched_instr),
@@ -50,7 +53,7 @@ module nqcpu (
 	);
 
 	always @(posedge clk) begin
-		if(fetch_ready) begin
+		if(incr_pc) begin
 			pc <= pc + 16'h2;
 		end
 	end
@@ -61,7 +64,7 @@ module nqcpu (
 
 	decoder_stage decoder_inst (
 		.clk(clk),
-		.en(fetch_ready),
+		.en(decode_en),
 		.instr_in(fetched_instr),
 		.pc_in(pc_from_fetch),
 		.control_signals_out(ctrl_from_decoder),
@@ -105,7 +108,7 @@ module nqcpu (
 	wire [15:0] pc_from_alu;
 	alu_stage alu_inst (
 		.clk(clk),
-		.en(1'b1),
+		.en(alu_en),
 		.pc_in(pc_from_decoder),
 		.control_signals_in(ctrl_from_decoder),
 		.imm_in(imm_from_decoder),
@@ -130,6 +133,20 @@ module nqcpu (
 		.pc_out(pc_from_alu)
 	);
 
+	control_unit control_unit_inst (
+		.clk(clk),
+		
+		.fetch_ready(fetch_ready),
+		
+		.fetch_en(fetch_en),
+		.decode_en(decode_en),
+		.alu_en(alu_en),
+		
+		.incr_pc(incr_pc),
+		
+		.dbg_state(dbg_state)
+	);
+
 	ctrl_decode debug_decode (
 		.control_signals(ctrl_from_alu),
 
-- 
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