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// This is a component of pluto_step, a hardware step waveform generator
// Copyright 2007 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 02111-1307 USA
module stepgen(clk, enable, position, velocity, dirtime, steptime, step, dir, tap);
`define STATE_STEP 0
`define STATE_DIRCHANGE 1
`define STATE_DIRWAIT 2
parameter W=12;
parameter F=10;
parameter T=5;
input clk, enable;
output [W+F-1:0] position; reg [W+F-1:0] position;
input [F:0] velocity;
input [T-1:0] dirtime, steptime;
input [1:0] tap;
output step, dir;
reg step, dir;
reg [T-1:0] timer;
reg [1:0] state;
reg ones;
wire dbit = velocity[F];
wire pbit = (tap == 0 ? position[F]
: (tap == 1 ? position[F+1]
: (tap == 2 ? position[F+2]
: position[F+3])));
wire [W+F-1:0] xvelocity = {{W{velocity[F]}}, {1{velocity[F-1:0]}}};
`ifdef TESTING
// for testing:
initial position = 1'b0;
initial state = `STATE_STEP;
initial timer = 0;
initial dir = 0;
initial ones = 0;
`endif
always @(posedge clk) begin
if(enable) begin
// $display("state=%d timer=%d position=%h velocity=%h dir=%d dbit=%d pbit=%d ones=%d", state, timer, position, xvelocity, dir, dbit, pbit, ones);
if((dir != dbit) && (pbit == ones)) begin
if(state == `STATE_DIRCHANGE) begin
if(timer == 0) begin
dir <= dbit;
timer <= dirtime;
state <= `STATE_DIRWAIT;
end else begin
timer <= timer - 1'd1;
end
end else begin
if(timer == 0) begin
step <= 0;
timer <= dirtime;
state <= `STATE_DIRCHANGE;
end else begin
timer <= timer - 1'd1;
end
end
end else if(state == `STATE_DIRWAIT) begin
if(timer == 0) begin
state <= `STATE_STEP;
end else begin
timer <= timer - 1'd1;
end
end else begin
if(timer == 0) begin
if(pbit != ones) begin
ones <= pbit;
step <= 1'd1;
timer <= steptime;
end else begin
step <= 0;
end
end else begin
timer <= timer - 1'd1;
end
if(dir == dbit)
position <= position + xvelocity;
end
end
end
endmodule
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