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/////////////////////////////////////////////////////////////////////
//// ////
//// Simple Asynchronous Serial Comm. Device ////
//// ////
//// ////
//// Author: Rudolf Usselmann ////
//// rudi@asics.ws ////
//// ////
//// ////
//// Downloaded from: http://www.opencores.org/cores/sasc/ ////
//// ////
/////////////////////////////////////////////////////////////////////
//// ////
//// Copyright (C) 2000-2002 Rudolf Usselmann ////
//// www.asics.ws ////
//// rudi@asics.ws ////
//// ////
//// 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 SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY ////
//// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED ////
//// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS ////
//// FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL THE AUTHOR ////
//// OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, ////
//// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES ////
//// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE ////
//// GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR ////
//// BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF ////
//// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT ////
//// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT ////
//// OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE ////
//// POSSIBILITY OF SUCH DAMAGE. ////
//// ////
/////////////////////////////////////////////////////////////////////
// CVS Log
//
// $Id: sasc_top.v,v 1.1.1.1 2002/09/16 16:16:42 rudi Exp $
//
// $Date: 2002/09/16 16:16:42 $
// $Revision: 1.1.1.1 $
// $Author: rudi $
// $Locker: $
// $State: Exp $
//
// Change History:
// $Log: sasc_top.v,v $
// Revision 1.1.1.1 2002/09/16 16:16:42 rudi
// Initial Checkin
//
//
//
//
//
//
//
//
`include "timescale.v"
/*
Serial IO Interface
===============================
RTS I Request To Send
CTS O Clear to send
TD I Transmit Data
RD O Receive Data
*/
module sasc_top( clk, rst,
// SIO
rxd_i, txd_o, cts_i, rts_o,
// External Baud Rate Generator
sio_ce, sio_ce_x4,
// Internal Interface
din_i, dout_o, re_i, we_i, full_o, empty_o);
input clk;
input rst;
input rxd_i;
output txd_o;
input cts_i;
output rts_o;
input sio_ce;
input sio_ce_x4;
input [7:0] din_i;
output [7:0] dout_o;
input re_i, we_i;
output full_o, empty_o;
///////////////////////////////////////////////////////////////////
//
// Local Wires and Registers
//
parameter START_BIT = 1'b0,
STOP_BIT = 1'b1,
IDLE_BIT = 1'b1;
wire [7:0] txd_p;
reg load;
reg load_r;
wire load_e;
reg [9:0] hold_reg;
wire txf_empty;
reg txd_o;
reg shift_en;
reg [3:0] tx_bit_cnt;
reg rxd_s, rxd_r;
wire start;
reg [3:0] rx_bit_cnt;
reg rx_go;
reg [9:0] rxr;
reg rx_valid, rx_valid_r;
wire rx_we;
wire rxf_full;
reg rts_o;
reg txf_empty_r;
reg shift_en_r;
reg rxd_r1, rxd_r2;
wire lock_en;
reg change;
reg rx_sio_ce_d, rx_sio_ce_r1, rx_sio_ce_r2, rx_sio_ce;
reg [1:0] dpll_state, dpll_next_state;
///////////////////////////////////////////////////////////////////
//
// IO Fifo's
//
sasc_fifo4 tx_fifo( .clk( clk ),
.rst( rst ),
.clr( 1'b0 ),
.din( din_i ),
.we( we_i ),
.dout( txd_p ),
.re( load_e ),
.full( full_o ),
.empty( txf_empty )
);
sasc_fifo4 rx_fifo( .clk( clk ),
.rst( rst ),
.clr( 1'b0 ),
.din( rxr[9:2] ),
.we( rx_we ),
.dout( dout_o ),
.re( re_i ),
.full( rxf_full ),
.empty( empty_o )
);
///////////////////////////////////////////////////////////////////
//
// Transmit Logic
//
always @(posedge clk)
if(!rst) txf_empty_r <= #1 1'b1;
else
if(sio_ce) txf_empty_r <= #1 txf_empty;
always @(posedge clk)
load <= #1 !txf_empty_r & !shift_en & !cts_i;
always @(posedge clk)
load_r <= #1 load;
assign load_e = load & sio_ce;
always @(posedge clk)
if(load_e) hold_reg <= #1 {STOP_BIT, txd_p, START_BIT};
else
if(shift_en & sio_ce) hold_reg <= #1 {IDLE_BIT, hold_reg[9:1]};
always @(posedge clk)
if(!rst) txd_o <= #1 IDLE_BIT;
else
if(sio_ce)
if(shift_en | shift_en_r) txd_o <= #1 hold_reg[0];
else txd_o <= #1 IDLE_BIT;
always @(posedge clk)
if(!rst) tx_bit_cnt <= #1 4'h9;
else
if(load_e) tx_bit_cnt <= #1 4'h0;
else
if(shift_en & sio_ce) tx_bit_cnt <= #1 tx_bit_cnt + 4'h1;
always @(posedge clk)
shift_en <= #1 (tx_bit_cnt != 4'h9);
always @(posedge clk)
if(!rst) shift_en_r <= #1 1'b0;
else
if(sio_ce) shift_en_r <= #1 shift_en;
///////////////////////////////////////////////////////////////////
//
// Recieve Logic
//
always @(posedge clk)
rxd_s <= #1 rxd_i;
always @(posedge clk)
rxd_r <= #1 rxd_s;
assign start = (rxd_r == IDLE_BIT) & (rxd_s == START_BIT);
always @(posedge clk)
if(!rst) rx_bit_cnt <= #1 4'ha;
else
if(!rx_go & start) rx_bit_cnt <= #1 4'h0;
else
if(rx_go & rx_sio_ce) rx_bit_cnt <= #1 rx_bit_cnt + 4'h1;
always @(posedge clk)
rx_go <= #1 (rx_bit_cnt != 4'ha);
always @(posedge clk)
rx_valid <= #1 (rx_bit_cnt == 4'h9);
always @(posedge clk)
rx_valid_r <= #1 rx_valid;
assign rx_we = !rx_valid_r & rx_valid & !rxf_full;
always @(posedge clk)
if(rx_go & rx_sio_ce) rxr <= {rxd_s, rxr[9:1]};
always @(posedge clk)
rts_o <= #1 rxf_full;
///////////////////////////////////////////////////////////////////
//
// Reciever DPLL
//
// Uses 4x baud clock to lock to incoming stream
// Edge detector
always @(posedge clk)
if(sio_ce_x4) rxd_r1 <= #1 rxd_s;
always @(posedge clk)
if(sio_ce_x4) rxd_r2 <= #1 rxd_r1;
always @(posedge clk)
if(!rst) change <= #1 1'b0;
else
if(rxd_r != rxd_s) change <= #1 1'b1;
else
if(sio_ce_x4) change <= #1 1'b0;
// DPLL FSM
always @(posedge clk or negedge rst)
if(!rst) dpll_state <= #1 2'h1;
else
if(sio_ce_x4) dpll_state <= #1 dpll_next_state;
always @(dpll_state or change)
begin
rx_sio_ce_d = 1'b0;
case(dpll_state)
2'h0:
if(change) dpll_next_state = 3'h0;
else dpll_next_state = 3'h1;
2'h1:begin
rx_sio_ce_d = 1'b1;
if(change) dpll_next_state = 3'h3;
else dpll_next_state = 3'h2;
end
2'h2:
if(change) dpll_next_state = 3'h0;
else dpll_next_state = 3'h3;
2'h3:
if(change) dpll_next_state = 3'h0;
else dpll_next_state = 3'h0;
endcase
end
// Compensate for sync registers at the input - allign sio
// clock enable to be in the middle between two bit changes ...
always @(posedge clk)
rx_sio_ce_r1 <= #1 rx_sio_ce_d;
always @(posedge clk)
rx_sio_ce_r2 <= #1 rx_sio_ce_r1;
always @(posedge clk)
rx_sio_ce <= #1 rx_sio_ce_r1 & !rx_sio_ce_r2;
endmodule
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