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/////////////////////////////////////////////////////////////////////
//// ////
//// Simple Baud Rate Generator ////
//// ////
//// ////
//// 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_brg.v,v 1.2 2002/11/08 15:22:49 rudi Exp $
//
// $Date: 2002/11/08 15:22:49 $
// $Revision: 1.2 $
// $Author: rudi $
// $Locker: $
// $State: Exp $
//
// Change History:
// $Log: sasc_brg.v,v $
// Revision 1.2 2002/11/08 15:22:49 rudi
//
// Fixed a typo in brg
//
// Revision 1.1.1.1 2002/09/16 16:16:40 rudi
// Initial Checkin
//
//
//
//
//
//
//
//
`include "timescale.v"
/*
Baud rate Generator
==================
div0 - is the first stage divider
Set this to the desired number of cycles less two
div1 - is the second stage divider
Set this to the actual number of cycles
Remember you have to generate a baud rate that is 4 higher than what
you really want. This is because of the DPLL in the RX section ...
Example:
If your system clock is 50MHz and you want to generate a 9.6 Kbps baud rate:
9600*4 = 38400KHz
50MHz/38400KHz=1302 or 6*217
set div0=4 (6-2) and set div1=217
*/
module sasc_brg(clk, rst, div0, div1, sio_ce, sio_ce_x4);
input clk;
input rst;
input [7:0] div0, div1;
output sio_ce, sio_ce_x4;
///////////////////////////////////////////////////////////////////
//
// Local Wires and Registers
//
reg [7:0] ps;
reg ps_clr;
reg [7:0] br_cnt;
reg br_clr;
reg sio_ce_x4_r;
reg [1:0] cnt;
reg sio_ce, sio_ce_x4;
reg sio_ce_r ;
reg sio_ce_x4_t;
///////////////////////////////////////////////////////////////////
//
// Boud Rate Generator
//
// -----------------------------------------------------
// Prescaler
always @(posedge clk)
if(!rst) ps <= #1 8'h0;
else
if(ps_clr) ps <= #1 8'h0;
else ps <= #1 ps + 8'h1;
always @(posedge clk)
ps_clr <= #1 (ps == div0); // Desired number of cycles less 2
// -----------------------------------------------------
// Oversampled Boud Rate (x4)
always @(posedge clk)
if(!rst) br_cnt <= #1 8'h0;
else
if(br_clr) br_cnt <= #1 8'h0;
else
if(ps_clr) br_cnt <= #1 br_cnt + 8'h1;
always @(posedge clk)
br_clr <= #1 (br_cnt == div1); // Prciese number of PS cycles
always @(posedge clk)
sio_ce_x4_r <= #1 br_clr;
always @(posedge clk)
sio_ce_x4_t <= #1 !sio_ce_x4_r & br_clr;
always @(posedge clk)
sio_ce_x4 <= #1 sio_ce_x4_t;
// -----------------------------------------------------
// Actual Boud rate
always @(posedge clk)
if(!rst) cnt <= #1 2'h0;
else
if(!sio_ce_x4_r & br_clr) cnt <= #1 cnt + 2'h1;
always @(posedge clk)
sio_ce_r <= #1 (cnt == 2'h0);
always @(posedge clk)
sio_ce <= #1 !sio_ce_r & (cnt == 2'h0);
endmodule