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　16ビット版VerilogによるK-COMの設計　

本で書いた16ビット版のK-COM16のVerilogによる設計例です．
サブルーチンコール，割り込み機能の追加，命令とアドレス空間を拡張しています．
（仕様の詳細は書籍をご参照いただければ幸いです）

クロックジェネレータ

module clock16(reset, gclk, tclk, sclk );
input	reset, gclk;
output	tclk, sclk;
reg		tclk, sclk;

always @(posedge gclk or posedge reset) if (reset) sclk <=0; else sclk <= ~sclk;
always @(negedge gclk or posedge reset) if (reset) tclk <=0; else tclk <= ~tclk;
endmodule

プログラムカウンタおよび命令レジスタ

module pcir16(reset, tclk, halt, pc, ir, a_bus, d_bus, select);
input reset, tclk;
input [9:0] select;
input [15:0] d_bus;
output halt;
output [11:0] a_bus;
output [11:0] pc;
output [15:0] ir;
reg [11:0] pc, as;
reg [15:0] ir;

always @(posedge tclk or posedge reset) begin
	if (reset) begin pc<=0; ir<=0; end 
	else begin
		if(select[4]) begin
			if(~select[8] & ~select[7]) pc<=pc+12'b1;
			if(~select[8] & select[7]) pc<=ir[11:0];
			if(select[8] & ~select[7]) pc<=as;
			if(select[8] & select[7]) pc<=12'hf00;
		end
		else if(select[9]) as<=pc;
		else if(select[3]) ir<=d_bus;
	end
end
assign a_bus=(select[0]) ? pc: ir[11:0];
assign halt=(ir==12'hfff);

endmodule

ALUおよびアキュームレータ

module alu16(reset, tclk, ir, select, acc, latch, c, z, d_bus);
input	reset, tclk;
input [9:0]		select;
input [15:0]	ir;
output [15:0]	acc, latch;
output			z, c;
inout [15:0]	d_bus;
reg				c, sc, z, sz;
reg [15:0]		acc, sacc, latch;

always	@(posedge tclk or posedge reset) begin
	if (reset) begin acc<=0; latch<=0; c<=0; z<=0; end
	else begin
		if(select[5]) begin
			casex(ir[15:12])
				4'b0000: begin {c,latch}<=acc + d_bus; z<=((acc + d_bus)==16'h0000); end
				4'b0001: begin {c,latch}<=acc - d_bus; z<=((acc - d_bus)==16'h0000); end
				4'b0010: begin {c,latch}<=~(acc & d_bus); z<=(~(acc & d_bus)==16'h0000); end
				4'b0011: begin {c,latch}<=acc << 1; z<=((acc <<1 )==16'h0000); end
				4'b1110: begin sacc<=acc; sc<=c; sz<=z; end
				4'b1111: begin acc<=sacc; c<=sc; z<=sz; end
				default: latch<=acc;
			endcase
		end
		if(select[6]) acc<=d_bus;
	end
end
assign d_bus= (select[1]) ? latch: 16'bz;
endmodule

メモリおよびI/Oポート

module mem16(tclk, a_bus, inp, oup, select, d_bus);
input tclk;
input [11:0] a_bus;
input [15:0] inp;
input [9:0] select;
output [15:0] oup;
inout [15:0] d_bus;
reg [15:0] mem[6:6] ;	// max size ... [0:4095]
reg [15:0] oup;

function [15:0] memout;  // memory read
input [11:0] a_bus;
	case(a_bus) 
		0:memout =16'h8FFE;	// LD   FFEH	ROM area
		1:memout =16'h0006;	// ADD  006H
		2:memout =16'h9FFF;	// ST   FFFH
		3:memout =16'h2006;	// NAND 005H
		4:memout =16'hB000;	// JPNZ 000H
		5:memout =16'h0000;	// DB 00 00H
		3840:memout =16'hE000;	// PUSH	  interupt routine
		3841:memout =16'h8FFE;	// LD FFEH
		3842:memout =16'h9006;	// ST 006H
		3843:memout =16'hF000;	// PULL
		3844:memout =16'hD000;	// RET
		4094:memout =inp;	// input port
		default: memout = mem[a_bus];
	endcase
endfunction 

always @(posedge tclk) begin
	if(select[2] & select[1]) // memory write
		if (a_bus==4095) oup<=d_bus; // output port
			else mem[a_bus]<=d_bus;
end
assign d_bus = (~select[2] & ~select[1])? memout(a_bus): 16'bz;

endmodule

コントローラ

module control16(reset, ipt, sclk, ir, c, z, select, i);
input	reset, ipt, sclk, c, z;
input 	[15:0] ir;
output 	i;
output 	[9:0] select;
reg  	i;
reg 	[2:0] ss;
reg 	[9:0] select;

// details of select signals
// select9: AS latch 
// select8: Return from sub-routine or interrupt
// select7: PC count-up or PC load (jump)	
// select6: ACC latch 
// select5: ALU latch
// select4: PC count up or load enable        
// select3: IR latch  
// select2: memory read(0)/write(1) 
// select1: ACC data select from ALU or memory 	
// select0: address select PC(1) or IR_L(0)

always @(posedge sclk or posedge reset) begin
	if (reset) begin ss<=3'b000; i<=0; end
	else case (ss)
		3'b000: 
			if(ipt & ~i) begin select<=10'b1000000000; ss<=3'b100; i<=1; end // interupt 1: as<-pc
				else     begin select<=10'b0000001001; ss<=3'b001; end	// fetch cycle 1

		3'b001: 		 begin select<=10'b0000010000; ss<=3'b010; end	// fetch cycle 2
		3'b010: 
			casex (ir[15:12])													// exec cycle 1
				4'b0XXX: begin select<=10'b0000100000; ss<=3'b011; end	// alu operation 1
				4'b1000: begin select<=10'b0001000000; ss<=3'b000; end	// LD
				4'b1001: begin select<=10'b0000100000; ss<=3'b011; end	// ST
				4'b1010: begin
				  if(~c) begin select<=10'b0000000000; ss<=3'b000; end	// JPC: c=0, nop
				  if(c)  begin select<=10'b0010010000; ss<=3'b000; end	// JPC: c=1, jump
				  end
				4'b1011: begin
				  if(~z) begin select<=10'b0010010000; ss<=3'b000; end	// JPNZ: z=0, jump
				  if(z)  begin select<=10'b0000000000; ss<=3'b000; end	// JPNZ: z=1, nop
			      end
				4'b1100: begin select<=10'b1000000000; ss<=3'b011; end	// CALL 1
				4'b1101: begin select<=10'b0100010000; ss<=3'b000; i<=0; end	// RET
				4'b1110: begin select<=10'b0000100000; ss<=3'b000; end	// PUSH
				4'b1111: begin select<=10'b0001100000; ss<=3'b000; end	// PULL
			endcase
		3'b011:																	
			casex (ir[15:12])													// exec cycle 2
				4'b0XXX: begin select<=10'b0001000010; ss<=3'b000; end	// alu operation 2
				4'b1001: begin select<=10'b0000000110; ss<=3'b000; end	// ST 2
				4'b1100: begin select<=10'b0010010000; ss<=3'b000; end	// CALL 2
			endcase	
		3'b100: 		 begin select<=10'b0110010000; ss<=3'b000; end	// interupt 2: pc<-F000H		
	endcase
end 

endmodule

K-COM16のトップモジュール

module kcom16(reset,ipt,clk,tclk,sclk,a_bus,pc,d_bus,ir,acc,latch,c,z,select,inp,oup,halt,i);
input reset, ipt, clk;
input [15:0] inp; 
output tclk, sclk, c, z, halt, i;
output [11:0] a_bus, pc;
output [9:0] select;
output [15:0] d_bus, ir, acc, latch, oup;
wire gclk;

assign gclk= clk & ~halt;
clock16 clock16(reset, gclk, tclk, sclk);
pcir16 pcir16(reset, tclk, halt, pc, ir, a_bus, d_bus, select);
alu16 alu16(reset, tclk, ir, select, acc, latch, c, z, d_bus);
mem16 mem16(tclk, a_bus, inp, oup, select, d_bus);
control16 control16(reset, ipt, sclk, ir, c, z, select, i);
  
endmodule
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