verilog/dv/agents/uart_agent.v

module uart_agent (
	mclk,
	txd,
	rxd
	);

input	mclk;
output	txd;

input	rxd;

event	uart_read_done, uart_write_done;
event	error_detected,uart_parity_error, uart_stop_error1, uart_stop_error2;
event 	uart_timeout_error;
event	abort;

reg [15:0] rx_count;
reg [15:0] tx_count;
reg [15:0] par_err_count;
reg [15:0] stop_err1_cnt;
reg [15:0] stop_err2_cnt;
reg [15:0] timeout_err_cnt;
reg [15:0] err_cnt;

reg 	   txd, read, write;
wire	   uart_rx_clk;
reg	   uart_clk;
reg	   stop_err_check;

integer timeout_count;
integer data_bit_number;
reg [15:0] clk_count;

reg      error_ind; // 1 indicate error

initial 
begin
	txd = 1'b1;
 	uart_clk = 0;
	clk_count = 0;
	stop_err_check = 0;
  error_ind = 0;
end

always @(posedge mclk)
begin
   if (clk_count == 'h0) begin
      uart_clk = ~uart_clk;
      clk_count = control_setup.divisor;	
   end else begin
      clk_count = clk_count - 1;	
   end
end
assign uart_rx_clk = ~uart_clk;

always @(posedge mclk)
begin
	timeout_count = timeout_count + 1;
	if (timeout_count == (control_setup.maxtime * 16))
		-> abort;
end

always @uart_read_done
    rx_count = rx_count + 1;

always @uart_write_done
    tx_count = tx_count + 1;

always @uart_parity_error begin
    error_ind = 1;
    par_err_count = par_err_count + 1;
end

always @uart_stop_error1 begin
    error_ind = 1;
    stop_err1_cnt = stop_err1_cnt + 1;
end

always @uart_stop_error2 begin
    error_ind = 1;
    stop_err2_cnt = stop_err2_cnt + 1;
end

always @uart_timeout_error begin
    error_ind = 1;
    timeout_err_cnt = timeout_err_cnt + 1;
end


always @error_detected begin
    error_ind = 1;
    err_cnt = err_cnt + 1;
end


////////////////////////////////////////////////////////////////////////////////
task uart_init;
begin
  read = 0;
  write = 0;
  tx_count = 0;
  rx_count = 0;
  stop_err_check = 0;
  par_err_count = 0;
  stop_err1_cnt = 0;
  stop_err2_cnt = 0;
  timeout_err_cnt = 0;
  err_cnt = 0;

end 
endtask 


////////////////////////////////////////////////////////////////////////////////
task read_char_chk;
input 	expected_data;

integer i;
reg	[7:0] expected_data;
reg 	[7:0] data;
reg	parity;

begin
	data <= 8'h0;
	parity <= 1;
	timeout_count = 0;

fork	
   begin : loop_1
        @(abort)
         $display ("%m: >>>>> Exceed time limit, uart no responce.\n");
         ->uart_timeout_error;
         disable loop_2;
   end

   begin : loop_2

// start cycle
	@(negedge rxd) 
	 disable loop_1;
	 read <= 1;

// data cycle
	@(posedge uart_rx_clk);
	 for (i = 0; i < data_bit_number; i = i + 1)
	  begin
	    @(posedge uart_rx_clk)
	    data[i] <=  rxd;
	    parity <= parity ^ rxd;
	  end		

// parity cycle
	if(control_setup.parity_en)
	begin
          @(posedge uart_rx_clk);
	  if ((control_setup.even_odd_parity && (rxd == parity)) ||
	     (!control_setup.even_odd_parity && (rxd != parity)))
	     begin
		$display ("%m: >>>>>  Parity Error");	
 		-> error_detected;
		-> uart_parity_error;
	     end
	end

// stop cycle 1
        @(posedge uart_rx_clk);	
	  if (!rxd)
	     begin
		$display ("%m: >>>>>  Stop signal 1 Error");	
 		-> error_detected;
		-> uart_stop_error1;
	     end

// stop cycle 2
	if (control_setup.stop_bit_number)
	begin
	      @(posedge uart_rx_clk);	// stop cycle 2
		if (!rxd)
		  begin
		    $display ("%m: >>>>>  Stop signal 2 Error");	
 		    -> error_detected;
		    -> uart_stop_error2;
		  end
	end


// wait another half cycle for tx_done signal
		@(negedge uart_rx_clk);
	read <= 0;
	-> uart_read_done;

	if (expected_data != data)
	begin
		$display ("%m: Error! Data return is %h, expecting %h", data, expected_data);
		-> error_detected;
	end
	else
		$display ("%m: Data match  %h", expected_data);

	$display ("%m:... Read Data from UART done cnt :%d...",rx_count +1);
   end
join

end

endtask


////////////////////////////////////////////////////////////////////////////////
task write_char;
input [7:0] data;

integer i;
reg parity;	// 0: odd parity, 1: even parity

begin
	parity <=  #1 1;

// start cycle
	@(posedge uart_clk)
	 begin
		txd <= #1 0;
		write <= #1 1;
	 end

// data cycle
	begin
	   for (i = 0; i < data_bit_number; i = i + 1)
	   begin
		@(posedge uart_clk)
		    txd <= #1 data[i];
		parity <= parity ^ data[i];
	   end
	end

// parity cycle
	if (control_setup.parity_en)
	begin
		@(posedge uart_clk)
			txd <= #1 
//				control_setup.stick_parity ? ~control_setup.even_odd_parity : 
				control_setup.even_odd_parity ? !parity : parity;
	end

// stop cycle 1
	@(posedge uart_clk)
		txd <= #1 stop_err_check ? 0 : 1;

// stop cycle 2
	@(posedge uart_clk);
		txd <= #1 1;
	if (data_bit_number == 5)
		@(negedge uart_clk);
	else if (control_setup.stop_bit_number)
		@(posedge uart_clk);

	write <= #1 0;
	$display ("%m:... Write data %h to UART done cnt : %d ...\n", data,tx_count+1);
	-> uart_write_done;
end
endtask


////////////////////////////////////////////////////////////////////////////////
task control_setup;
input	  [1:0] data_bit_set;	
input		stop_bit_number;
input		parity_en;
input		even_odd_parity;
input		stick_parity;
input	 [15:0] maxtime;
input	 [15:0] divisor;

begin
        clk_count = divisor;	
	data_bit_number = data_bit_set + 5;
end
endtask


////////////////////////////////////////////////////////////////////////////////
task report_status;
output 	[15:0] rx_nu;
output 	[15:0] tx_nu;
begin
	$display ("-------------------- UART Reporting Configuration --------------------");
	$display ("	Data bit number setting is : %0d", data_bit_number);
	$display ("	Stop bit number setting is : %0d", control_setup.stop_bit_number + 1);
	$display ("	Divisor of Uart clock   is : %0d", control_setup.divisor);
	if (control_setup.parity_en) 
	$display ("	Parity is enable");
	else
	$display ("	Parity is disable");
	
	if (control_setup.even_odd_parity)
	$display ("	Even parity setting");
	else	
	$display ("	Odd parity setting");


	$display ("-----------------------------------------------------------------");

	$display ("-------------------- Reporting Status --------------------\n");
	$display ("	Number of character received is : %d", rx_count);
	$display ("	Number of character sent     is : %d", tx_count);
	$display ("	Number of parity error rxd   is : %d", par_err_count);
	$display ("	Number of stop1  error rxd   is : %d", stop_err1_cnt);
	$display ("	Number of stop2  error rxd   is : %d", stop_err2_cnt);
	$display ("	Number of timeout error      is : %d", timeout_err_cnt);
	$display ("	Number of error              is : %d", err_cnt);
	$display ("-----------------------------------------------------------------");

	rx_nu = rx_count;
	tx_nu = tx_count;
end
endtask


////////////////////////////////////////////////////////////////////////////////
endmodule