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// This is a component of pluto_servo, a PWM servo driver and quadrature
// counter for emc2
// Copyright 2006 Jeff Epler <jepler@unpythonic.net>
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// This program 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 General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1507 USA
module quad(clk, A, B, Z, zr, out);
parameter W=14;
input clk, A, B, Z, zr;
reg [(W-1):0] c, i; reg zl;
output [2*W:0] out = { zl, i, c };
// reg [(W-1):0] c, i; reg zl;
reg [2:0] Ad, Bd;
reg [2:0] Zc;
always @(posedge clk) Ad <= {Ad[1:0], A};
always @(posedge clk) Bd <= {Bd[1:0], B};
wire good_one = &Zc;
wire good_zero = ~|Zc;
reg last_good;
wire index_pulse = good_one && ! last_good;
wire count_enable = Ad[1] ^ Ad[2] ^ Bd[1] ^ Bd[2];
wire count_direction = Ad[1] ^ Bd[2];
always @(posedge clk)
begin
if(Z && !good_one) Zc <= Zc + 2'b1;
else if(!good_zero) Zc <= Zc - 2'b1;
if(good_one) last_good <= 1;
else if(good_zero) last_good <= 0;
if(count_enable)
begin
if(count_direction) c <= c + 1'd1;
else c <= c - 1'd1;
end
if(index_pulse) begin
i <= c;
zl <= 1;
end else if(zr) begin
zl <= 0;
end
end
endmodule
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