class spi_driver;

  static bit		my_cmd=1'b0;
  static bit[24:0]	last_addr;
  static bit		last_s;

  //MOSI data pkt, other input_signals are not packed
  spi_trans  		m_trans;

  //interface
  virtual spi_if 	vif;

  //MOSI data_stream input to SPI(DUT)
  bit			stream[$];

  //parameter for randomization
       int		pktnum;
       int		interval;
  rand int		error_time;
       int		half_sclk;
       bit		autarchy;

  

  constraint cstr{
    error_time  <=  544;
    error_time  >=  -544;
  }

  function new();
  endfunction
  extern task do_drive();
  extern task make_pkt(spi_trans tr);

endclass : spi_driver 


task spi_driver::do_drive();

  $display("pkt_num:\t%0d",pktnum);

  while(!vif.rstn) begin
    vif.csn  = 1'b1;
    vif.sclk = 1'b1;
    @(posedge vif.clk);
  end

  while(pktnum>0) begin
    
    //$display(my_cmd);
    make_pkt(m_trans);

    repeat(interval) 
      @(posedge vif.clk);

    pktnum--;
  end

endtask : do_drive


task spi_driver::make_pkt(spi_trans tr);
  int i=0,j=0;
  int cs_time,mo_time;


  //**********************Create and Randomize a pkt**********************//
  tr = new();

  if(!tr.randomize() with {
    cmd==my_cmd;
    (cmd==1'b0 || s==last_s);
    (cmd==1'b0 || addr==last_addr);
    addr[24:20] == 5'b00000 || 
    addr[24:20] == 5'b00001 ||
    addr[24:20] == 5'b00010;
  })
    $fatal(0,"Randomize Failed");

  if(tr.cmd == 1'b0) begin
    last_addr = tr.addr;
    last_s    = tr.s;
  end

  my_cmd = ~my_cmd;
  

  //Autarchy: Testcase force to assign some params
  interval 	= tr.interval;
  if(!autarchy) begin
    half_sclk	= tr.half_sclk;
  end


  //*****************initialize chip_select and input_clk******************//
  vif.csn  <= 1'b1;
  vif.sclk <= 1'b1;
  vif.mosi <= stream[0];
  @(posedge vif.clk);
  vif.csn  <= 1'b0;
  vif.sclk <= 1'b1;

  //unpack into bitstream
  stream.delete();
  tr.unpack(stream);

  //mosi valid time: time for bitstream to be all sent
  //csn valid_time: maybe a delay after or ahead of mosi_finished
  mo_time = (stream.size())*2*half_sclk;
  cs_time = (pktnum==1) ? (mo_time + error_time%mo_time) : mo_time;

  	$display("***************************ONE PKT DRIVERED***************************");
  	$display("half_sclk:\t%0d\t\t\t\t\t\t    **",half_sclk);
  	$display("interval:\t%0d\t\t\t\t\t\t    **",interval);
  	//$display("error_time:\t%0d\t\t\t\t\t\t    **",error_time);
  	//$display("data_size:\t%0d\t\t\t\t\t\t    **",tr.data.size());
  	//$display("cmd:\t\t%0d\t\t\t\t\t\t    **",tr.cmd);
	//$display(stream);
  	if(!tr.cmd)
  	  for(i=0;i<tr.data.size;i++)
  	    $display("mosi:\t\t%32b\t\t    **",tr.data[i]);

  //********************drive the stream onto interface********************//
  fork


    //************************Make sclk************************//
    begin
       for(j=0;j<cs_time;j++) begin
          if(j % half_sclk == 0 && j!=0)
            vif.sclk <= ~vif.sclk;
	  @(posedge vif.clk);
       end
       vif.sclk  = 1'b1;
       @(posedge vif.clk);
       vif.csn = 1'b1;
    end

    //************************Send data************************//
    begin
       for(i=0;i<mo_time;i++) begin
 
	  //send data: 
	  //  data will be sampled at posedge,
	  //  so prepare them at the negedge before each posedge
          if(i % (2*half_sclk) == half_sclk)begin
             vif.mosi <= stream[(i/half_sclk-1)/2];
	     //$display(i);
	  end
          @(posedge vif.clk);

       end
    end


  join
  
	$display("**********************************************************************");

endtask