//----------------------------------------------------------------------------
module  machine( inc_pc, load_acc, load_pc, rd,wr, load_ir,
datactl_ena, halt, clk1, zero, ena, opcode );

output inc_pc, load_acc, load_pc, rd, wr, load_ir;
output datactl_ena, halt;
input clk1, zero, ena;
input [2:0] opcode;
reg inc_pc, load_acc, load_pc, rd, wr, load_ir;
reg datactl_ena, halt;
reg [2:0] state;

parameter   HLT  = 3 'b000,
  SKZ  = 3 'b001,
  ADD  = 3 'b010,
  ANDD = 3 'b011,
  XORR = 3 'b100,
  LDA  = 3 'b101,
  STO  = 3 'b110,
  JMP  = 3 'b111;

always @( negedge clk1 )
begin
if ( !ena )		//???????RST???????
begin
state<=3'b000;
{inc_pc,load_acc,load_pc,rd}<=4'b0000;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end
else
ctl_cycle;
end
//-----------------begin of task ctl_cycle---------
task ctl_cycle;
begin
casex(state)
    3'b000:          //load high 8bits in struction
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0001;
{wr,load_ir,datactl_ena,halt}<=4'b0100;
state<=3'b001;
end
    3'b001:		//pc increased by one then load low 8bits instruction
begin
{inc_pc,load_acc,load_pc,rd}<=4'b1001;
{wr,load_ir,datactl_ena,halt}<=4'b0100;
state<=3'b010;
end
    3'b010:		//idle
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0000;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
state<=3'b011;
end

    3'b011:		//next instruction address setup ?????????
begin
if(opcode==HLT)	//?????HLT
begin
{inc_pc,load_acc,load_pc,rd}<=4'b1000;
{wr,load_ir,datactl_ena,halt}<=4'b0001;
end	
else
begin
{inc_pc,load_acc,load_pc,rd}<=4'b1000;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end	
state<=3'b100;
end
    3'b100:			//fetch oprand
begin
if(opcode==JMP)
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0010;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end
else
if( opcode==ADD || opcode==ANDD || 
opcode==XORR || opcode==LDA)
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0001;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end	
else 
if(opcode==STO)
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0000;
{wr,load_ir,datactl_ena,halt}<=4'b0010;
end	
else
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0000;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end	
state<=3'b101;
end
   3'b101:		//operation
begin
if ( opcode==ADD||opcode==ANDD||
opcode==XORR||opcode==LDA )
begin		//?????????????????
{inc_pc,load_acc,load_pc,rd}<=4'b0101;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end	
else
if( opcode==SKZ && zero==1)
begin
{inc_pc,load_acc,load_pc,rd}<=4'b1000;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end	
else
if(opcode==JMP)
begin
{inc_pc,load_acc,load_pc,rd}<=4'b1010;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end	
else
if(opcode==STO)
begin
//???????wr?1????RAM?
{inc_pc,load_acc,load_pc,rd}<=4'b0000;
{wr,load_ir,datactl_ena,halt}<=4'b1010;
end	
else
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0000;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end	
state<=3'b110;
end
3'b110:		//idle
begin
if ( opcode==STO )
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0000;
{wr,load_ir,datactl_ena,halt}<=4'b0010;
end
else
if ( opcode==ADD||opcode==ANDD||
opcode==XORR||opcode==LDA)
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0001;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end
else
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0000;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end
state<=3'b111;
end

3'b111:		//
begin
if( opcode==SKZ && zero==1 )
begin
{inc_pc,load_acc,load_pc,rd}<=4'b1000;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end
else
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0000;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
end
state<=3'b000;
end
default:
begin
{inc_pc,load_acc,load_pc,rd}<=4'b0000;
{wr,load_ir,datactl_ena,halt}<=4'b0000;
state<=3'b000;
end
endcase
end
endtask
//-----------------end of task ctl_cycle---------

endmodule
//------------------------------------------------------------------------------