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A tiny Open POWER ISA softcore written in VHDL 2008
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microwatt/uart16550/uart_wb.v

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//////////////////////////////////////////////////////////////////////
//// ////
//// uart_wb.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 WISHBONE interface. ////
//// ////
//// Known problems (limits): ////
//// Inserts one wait state on all transfers. ////
//// Note affected signals and the way they are affected. ////
//// ////
//// To Do: ////
//// Nothing. ////
//// ////
//// 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 1.16 2002/07/29 21:16:18 gorban
// The uart_defines.v file is included again in sources.
//
// Revision 1.15 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 1.12 2001/12/19 08:03:34 mohor
// Warnings cleared.
//
// Revision 1.11 2001/12/06 14:51:04 gorban
// Bug in LSR[0] is fixed.
// All WISHBONE signals are now sampled, so another wait-state is introduced on all transfers.
//
// Revision 1.10 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 1.9 2001/10/20 09:58:40 gorban
// Small synopsis fixes
//
// Revision 1.8 2001/08/24 21:01:12 mohor
// Things connected to parity changed.
// Clock devider changed.
//
// Revision 1.7 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 1.4 2001/05/31 20:08:01 gorban
// FIFO changes and other corrections.
//
// Revision 1.3 2001/05/21 19:12:01 gorban
// Corrected some Linter messages.
//
// Revision 1.2 2001/05/17 18:34:18 gorban
// First 'stable' release. Should be sythesizable now. Also added new header.
//
// Revision 1.0 2001-05-17 21:27:13+02 jacob
// Initial revision
//
//
// UART core WISHBONE interface
//
// Author: Jacob Gorban (jacob.gorban@flextronicssemi.com)
// Company: Flextronics Semiconductor
//
`include "uart_defines.v"
module uart_wb (clk, wb_rst_i,
wb_we_i, wb_stb_i, wb_cyc_i, wb_ack_o, wb_adr_i,
wb_adr_int, wb_dat_i, wb_dat_o, wb_dat8_i, wb_dat8_o, wb_dat32_o, wb_sel_i,
we_o, re_o // Write and read enable output for the core
);
input clk;
// WISHBONE interface
input wb_rst_i;
input wb_we_i;
input wb_stb_i;
input wb_cyc_i;
input [3:0] wb_sel_i;
input [2:0] wb_adr_i; //WISHBONE address line
input [7:0] wb_dat_i; //input WISHBONE bus
output [7:0] wb_dat_o;
reg [7:0] wb_dat_o;
wire [7:0] wb_dat_i;
reg [7:0] wb_dat_is;
output [2:0] wb_adr_int; // internal signal for address bus
input [7:0] wb_dat8_o; // internal 8 bit output to be put into wb_dat_o
output [7:0] wb_dat8_i;
input [31:0] wb_dat32_o; // 32 bit data output (for debug interface)
output wb_ack_o;
output we_o;
output re_o;
wire we_o;
reg wb_ack_o;
reg [7:0] wb_dat8_i;
wire [7:0] wb_dat8_o;
wire [2:0] wb_adr_int; // internal signal for address bus
reg [2:0] wb_adr_is;
reg wb_we_is;
reg wb_cyc_is;
reg wb_stb_is;
wire [3:0] wb_sel_i;
reg wre ;// timing control signal for write or read enable
// wb_ack_o FSM
reg [1:0] wbstate;
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) begin
wb_ack_o <= 1'b0;
wbstate <= 0;
wre <= 1'b1;
end else
case (wbstate)
0: begin
if (wb_stb_is & wb_cyc_is) begin
wre <= 0;
wbstate <= 1;
wb_ack_o <= 1;
end else begin
wre <= 1;
wb_ack_o <= 0;
end
end
1: begin
wb_ack_o <= 0;
wbstate <= 2;
wre <= 0;
end
2: begin
wb_ack_o <= 0;
wbstate <= 3;
wre <= 0;
end
3: begin
wb_ack_o <= 0;
wbstate <= 0;
wre <= 1;
end
endcase
assign we_o = wb_we_is & wb_stb_is & wb_cyc_is & wre ; //WE for registers
assign re_o = ~wb_we_is & wb_stb_is & wb_cyc_is & wre ; //RE for registers
// Sample input signals
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i) begin
wb_adr_is <= 0;
wb_we_is <= 0;
wb_cyc_is <= 0;
wb_stb_is <= 0;
wb_dat_is <= 0;
end else begin
wb_adr_is <= wb_adr_i;
wb_we_is <= wb_we_i;
wb_cyc_is <= wb_cyc_i;
wb_stb_is <= wb_stb_i;
wb_dat_is <= wb_dat_i;
end
always @(posedge clk or posedge wb_rst_i)
if (wb_rst_i)
wb_dat_o <= 0;
else
wb_dat_o <= wb_dat8_o;
always @(wb_dat_is)
wb_dat8_i = wb_dat_is;
assign wb_adr_int = wb_adr_is;
endmodule