verilog/rtl/uart_transmitter.v

//////////////////////////////////////////////////////////////////////
////                                                              ////
////  uart_transmitter.v                                          ////
////                                                              ////
////                                                              ////
////  This file is part of the "UART 16550 compatible" project    ////
////  http://www.opencores.org/cores/uart16550/                   ////
////                                                              ////
////  Documentation related to this project:                      ////
////  - http://www.opencores.org/cores/uart16550/                 ////
////                                                              ////
////  Projects compatibility:                                     ////
////  - WISHBONE                                                  ////
////  RS232 Protocol                                              ////
////  16550D uart (mostly supported)                              ////
////                                                              ////
////  Overview (main Features):                                   ////
////  UART core transmitter logic                                 ////
////                                                              ////
////  Known problems (limits):                                    ////
////  None known                                                  ////
////                                                              ////
////  To Do:                                                      ////
////  Thourough testing.                                          ////
////                                                              ////
////  Author(s):                                                  ////
////      - gorban@opencores.org                                  ////
////      - Jacob Gorban                                          ////
////      - Igor Mohor (igorm@opencores.org)                      ////
////                                                              ////
////  Created:        2001/05/12                                  ////
////  Last Updated:   2001/05/17                                  ////
////                  (See log for the revision history)          ////
////                                                              ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
////                                                              ////
//// Copyright (C) 2000, 2001 Authors                             ////
////                                                              ////
//// This source file may be used and distributed without         ////
//// restriction provided that this copyright statement is not    ////
//// removed from the file and that any derivative work contains  ////
//// the original copyright notice and the associated disclaimer. ////
////                                                              ////
//// This source file is free software; you can redistribute it   ////
//// and/or modify it under the terms of the GNU Lesser General   ////
//// Public License as published by the Free Software Foundation; ////
//// either version 2.1 of the License, or (at your option) any   ////
//// later version.                                               ////
////                                                              ////
//// This source is distributed in the hope that it will be       ////
//// useful, but WITHOUT ANY WARRANTY; without even the implied   ////
//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR      ////
//// PURPOSE.  See the GNU Lesser General Public License for more ////
//// details.                                                     ////
////                                                              ////
//// You should have received a copy of the GNU Lesser General    ////
//// Public License along with this source; if not, download it   ////
//// from http://www.opencores.org/lgpl.shtml                     ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
//
// CVS Revision History
//
// $Log: not supported by cvs2svn $
// Revision 1.18  2002/07/22 23:02:23  gorban
// Bug Fixes:
//  * Possible loss of sync and bad reception of stop bit on slow baud rates fixed.
//   Problem reported by Kenny.Tung.
//  * Bad (or lack of ) loopback handling fixed. Reported by Cherry Withers.
//
// Improvements:
//  * Made FIFO's as general inferrable memory where possible.
//  So on FPGA they should be inferred as RAM (Distributed RAM on Xilinx).
//  This saves about 1/3 of the Slice count and reduces P&R and synthesis times.
//
//  * Added optional baudrate output (baud_o).
//  This is identical to BAUDOUT* signal on 16550 chip.
//  It outputs 16xbit_clock_rate - the divided clock.
//  It's disabled by default. Define UART_HAS_BAUDRATE_OUTPUT to use.
//
// Revision 1.16  2002/01/08 11:29:40  mohor
// tf_pop was too wide. Now it is only 1 clk cycle width.
//
// Revision 1.15  2001/12/17 14:46:48  mohor
// overrun signal was moved to separate block because many sequential lsr
// reads were preventing data from being written to rx fifo.
// underrun signal was not used and was removed from the project.
//
// Revision 1.14  2001/12/03 21:44:29  gorban
// Updated specification documentation.
// Added full 32-bit data bus interface, now as default.
// Address is 5-bit wide in 32-bit data bus mode.
// Added wb_sel_i input to the core. It's used in the 32-bit mode.
// Added debug interface with two 32-bit read-only registers in 32-bit mode.
// Bits 5 and 6 of LSR are now only cleared on TX FIFO write.
// My small test bench is modified to work with 32-bit mode.
//
// Revision 1.13  2001/11/08 14:54:23  mohor
// Comments in Slovene language deleted, few small fixes for better work of
// old tools. IRQs need to be fix.
//
// Revision 1.12  2001/11/07 17:51:52  gorban
// Heavily rewritten interrupt and LSR subsystems.
// Many bugs hopefully squashed.
//
// Revision 1.11  2001/10/29 17:00:46  gorban
// fixed parity sending and tx_fifo resets over- and underrun
//
// Revision 1.10  2001/10/20 09:58:40  gorban
// Small synopsis fixes
//
// Revision 1.9  2001/08/24 21:01:12  mohor
// Things connected to parity changed.
// Clock devider changed.
//
// Revision 1.8  2001/08/23 16:05:05  mohor
// Stop bit bug fixed.
// Parity bug fixed.
// WISHBONE read cycle bug fixed,
// OE indicator (Overrun Error) bug fixed.
// PE indicator (Parity Error) bug fixed.
// Register read bug fixed.
//
// Revision 1.6  2001/06/23 11:21:48  gorban
// DL made 16-bit long. Fixed transmission/reception bugs.
//
// Revision 1.5  2001/06/02 14:28:14  gorban
// Fixed receiver and transmitter. Major bug fixed.
//
// Revision 1.4  2001/05/31 20:08:01  gorban
// FIFO changes and other corrections.
//
// Revision 1.3  2001/05/27 17:37:49  gorban
// Fixed many bugs. Updated spec. Changed FIFO files structure. See CHANGES.txt file.
//
// Revision 1.2  2001/05/21 19:12:02  gorban
// Corrected some Linter messages.
//
// Revision 1.1  2001/05/17 18:34:18  gorban
// First 'stable' release. Should be sythesizable now. Also added new header.
//
// Revision 1.0  2001-05-17 21:27:12+02  jacob
// Initial revision
//
//

`include "uart_defines.v"

module uart_transmitter
#(parameter SIM = 0)
 (clk, wb_rst_i, lcr, tf_push, wb_dat_i, enable,	stx_pad_o, tstate, tf_count, tx_reset, lsr_mask);

input 										clk;
input 										wb_rst_i;
input [7:0] 								lcr;
input 										tf_push;
input [7:0] 								wb_dat_i;
input 										enable;
input 										tx_reset;
input 										lsr_mask; //reset of fifo
output 										stx_pad_o;
output [2:0] 								tstate;
output [`UART_FIFO_COUNTER_W-1:0] 	tf_count;

reg [2:0] 									tstate;
reg [4:0] 									counter;
reg [2:0] 									bit_counter;   // counts the bits to be sent
reg [6:0] 									shift_out;	// output shift register
reg 											stx_o_tmp;
reg 											parity_xor;  // parity of the word
reg 											tf_pop;
reg 											bit_out;

// TX FIFO instance
//
// Transmitter FIFO signals
wire [`UART_FIFO_WIDTH-1:0] 			tf_data_in;
wire [`UART_FIFO_WIDTH-1:0] 			tf_data_out;
wire 											tf_push;
wire 											tf_overrun;
wire [`UART_FIFO_COUNTER_W-1:0] 		tf_count;

assign 										tf_data_in = wb_dat_i;

uart_tfifo fifo_tx(	// error bit signal is not used in transmitter FIFO
	.clk(		clk		), 
	.wb_rst_i(	wb_rst_i	),
	.data_in(	tf_data_in	),
	.data_out(	tf_data_out	),
	.push(		tf_push		),
	.pop(		tf_pop		),
	.overrun(	tf_overrun	),
	.count(		tf_count	),
	.fifo_reset(	tx_reset	),
	.reset_status(lsr_mask)
);

// TRANSMITTER FINAL STATE MACHINE

localparam s_idle        = 3'd0;
localparam s_send_start  = 3'd1;
localparam s_send_byte   = 3'd2;
localparam s_send_parity = 3'd3;
localparam s_send_stop   = 3'd4;
localparam s_pop_byte    = 3'd5;

always @(posedge clk or posedge wb_rst_i)
begin
  if (wb_rst_i)
  begin
	tstate       <= s_idle;
	stx_o_tmp       <= 1'b1;
	counter   <= 5'b0;
	shift_out   <= 7'b0;
	bit_out     <= 1'b0;
	parity_xor  <= 1'b0;
	tf_pop      <= 1'b0;
	bit_counter <= 3'b0;
  end
  else
  if (enable | SIM)
  begin
	case (tstate)
	s_idle	 :	if (~|tf_count) // if tf_count==0
			begin
				tstate <= s_idle;
				stx_o_tmp <= 1'b1;
			end
			else
			begin
				tf_pop <= 1'b0;
				stx_o_tmp  <= 1'b1;
				tstate  <= s_pop_byte;
			end
	s_pop_byte :	begin
				tf_pop <= 1'b1;
				case (lcr[/*`UART_LC_BITS*/1:0])  // number of bits in a word
				2'b00 : begin
					bit_counter <= 3'b100;
					parity_xor  <= ^tf_data_out[4:0];
				     end
				2'b01 : begin
					bit_counter <= 3'b101;
					parity_xor  <= ^tf_data_out[5:0];
				     end
				2'b10 : begin
					bit_counter <= 3'b110;
					parity_xor  <= ^tf_data_out[6:0];
				     end
				2'b11 : begin
					bit_counter <= 3'b111;
					parity_xor  <= ^tf_data_out[7:0];
				     end
				endcase
				{shift_out[6:0], bit_out} <= tf_data_out;
				tstate <= s_send_start;
			end
	s_send_start :	begin
				tf_pop <= 1'b0;
				if (~|counter)
					counter <= 5'b01111;
				else
				if (counter == 5'b00001)
				begin
					counter <= 0;
					tstate <= s_send_byte;
				end
				else
					counter <= counter - 5'd1;
				stx_o_tmp <= 1'b0;
				if (SIM) begin
					tstate <= s_idle;
					$write("%c", tf_data_out);
					$fflush(32'h80000001);
				end
			end
	s_send_byte :	begin
				if (~|counter)
					counter <= 5'b01111;
				else
				if (counter == 5'b00001)
				begin
					if (bit_counter > 3'b0)
					begin
						bit_counter <= bit_counter - 3'd1;
						{shift_out[5:0],bit_out  } <= {shift_out[6:1], shift_out[0]};
						tstate <= s_send_byte;
					end
					else   // end of byte
					if (~lcr[`UART_LC_PE])
					begin
						tstate <= s_send_stop;
					end
					else
					begin
						case ({lcr[`UART_LC_EP],lcr[`UART_LC_SP]})
						2'b00:	bit_out <= ~parity_xor;
						2'b01:	bit_out <= 1'b1;
						2'b10:	bit_out <= parity_xor;
						2'b11:	bit_out <= 1'b0;
						endcase
						tstate <= s_send_parity;
					end
					counter <= 0;
				end
				else
					counter <= counter - 5'd1;
				stx_o_tmp <= bit_out; // set output pin
			end
	s_send_parity :	begin
				if (~|counter)
					counter <= 5'b01111;
				else
				if (counter == 5'b00001)
				begin
					counter <= 5'd0;
					tstate <= s_send_stop;
				end
				else
					counter <= counter - 5'd1;
				stx_o_tmp <= bit_out;
			end
	s_send_stop :  begin
				if (~|counter)
				  begin
						casez ({lcr[`UART_LC_SB],lcr[`UART_LC_BITS]})
  						3'b0??:	  counter <= 5'b01101;     // 1 stop bit ok igor
  						3'b100:	  counter <= 5'b10101;     // 1.5 stop bit
  						default:	  counter <= 5'b11101;     // 2 stop bits
						endcase
					end
				else
				if (counter == 5'b00001)
				begin
					counter <= 0;
					tstate <= s_idle;
				end
				else
					counter <= counter - 5'd1;
				stx_o_tmp <= 1'b1;
			end

		default : // should never get here
			tstate <= s_idle;
	endcase
  end // end if enable
  else
    tf_pop <= 1'b0;  // tf_pop must be 1 cycle width
end // transmitter logic

assign stx_pad_o = lcr[`UART_LC_BC] ? 1'b0 : stx_o_tmp;    // Break condition
	
endmodule