// Copyright 2006, 2007 Dennis van Weeren//// This file is part of Minimig//// Minimig 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 3 of the License, or// (at your option) any later version.//// Minimig 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, see <http://www.gnu.org/licenses/>.////JB:// 2008-03-14		- moving beamcounter to a separate file//					- pal/ntsc switching, NTSC doesn't use short/long line toggling,all lines are short like in PAL (227 CCK's)
//					- composite blanking use hblank which is combined with vblank
//beam counters and sync generatormodule beamcounter(	input	clk,				//bus clock	input	reset,				//reset	input	interlace,			//interlace enable	input	ntsc,				//ntsc mode switch	input	[15:0]datain,		//bus data in	output	reg [15:0]dataout,//bus data out	input 	[8:1]regaddressin,//register address inputs	output	reg [8:0]hpos,	//horizontal (low resolution) beam counter	output	reg [10:0]vpos,	//vertical beam counter	output	reg _hsync,		//horizontal sync	output	reg _vsync,		//vertical sync	output	blank,				//video blanking	output	vbl,				//vertical blanking	output	vblend,				//last line of vertival blanking	output	eol,				//start of video line (active during last pixel of previous line) 	output	eof					//start of video frame (active during last pixel of previous frame));//local signals for beam counters and sync generatorreg		hblank;			//horizontal blankingwire	vblank;			//vertical blankingreg		lof;			//1=long frame (313 lines), 0=normal frame (312 lines)reg		pal;			//pal mode switch
reg		lol;			//long line signal for NTSC compatibility//register names and adresses		parameter VPOSR = 9'h004;parameter VHPOSR = 9'h006;parameter BEAMCON0 = 9'h1DC;parameter	hbstrt  = 17;			// horizontal blanking startparameter	hsstrt  = 29;			// front porch = 1.6us (29)parameter	hsstop  = 63;			// hsync pulse duration = 4.7us (63)parameter	hbstop  = 92;			// back porch = 4.7us (103) shorter blanking for overscan visibilityparameter	hcenter = 254;			// position of vsync pulse during the long field of interlaced screenparameter	htotal  = 453;			// line length = 227 colour clocks in PAL (in NTSC 227.5 colour clocks: not supported)parameter	vsstrt  = 3;			//vertical sync startparameter	vsstop  = 5;			// pal vsync width: 2.5 lines (NTSC: 3 lines - not implemented)parameter	vbstrt  = 0;			//vertical blanking startwire	[8:0]vtotal;		//total number of lines less onewire	[8:0]vbstop;		//vertical blanking stopassign	vtotal  = pal ? 312-1 : 262-1;	//total number of lines (PAL: 312 lines, NTSC: 262)assign	vbstop  = pal ? 25 : 20;	//vertical blanking end (PAL 26 lines, NTSC vblank 21 lines)//A4k test: first visible line $1A (PAL) or $15 (NTSC)//sprites fetched on line $19 (PAL) or $14 (NTSC)//--------------------------------------------------------------------------------------//beamcounter read registers VPOSR and VHPOSRalways @(regaddressin or lof or vpos or hpos or ntsc)	if(regaddressin[8:1]==VPOSR[8:1])		dataout[15:0] = {lof,ntsc?7'h30:7'h20,lol,4'b0000,vpos[10:8]};	else	if(regaddressin[8:1]==VHPOSR[8:1])		dataout[15:0] = {vpos[7:0],hpos[8:1]};	else		dataout[15:0]=0;		//BEAMCON0 registeralways @(posedge clk)	if (reset)		pal <= ~ntsc;	else if (regaddressin[8:1] == BEAMCON0[8:1])		pal <= datain[5];		//--------------------------------------------------------------------------------------//horizontal beamcounter (runs @ clk frequency!)always @(posedge clk)	if (eol)		hpos <= 0;	else		hpos <= hpos + 1;//generate start of line signalassign eol = hpos==htotal ? 1 : 0;
//long line signal (not used, only for better NTSC compatibility)
always @(posedge clk)	if (eol)
		if (pal)			lol <= 0;
		else
			lol <= ~lol;//horizontal sync and horizontal blankingalways @(posedge clk)//sync	if (hpos==hsstrt)//start of sync pulse (front porch = 1.69us)		_hsync <= 0;	else if (hpos==hsstop)//end of sync pulse	(sync pulse = 4.65us)		_hsync <= 1;		always @(posedge clk)//blank	if(hpos==hbstrt)//start of blanking (active line=51.88us)		hblank <= 1;	else if (hpos==hbstop)//end of blanking (back porch=5.78us)		hblank <= vblank;//--------------------------------------------------------------------------------------//vertical beamcounter (triggered by eol signal from horizontal beamcounter)always @(posedge clk)	if (eof)		vpos <= 0;	else if (eol)		vpos <= vpos + 1;// lof - Long Frame signalalways @(posedge clk)	if (eof)		if (interlace)			lof <= ~lof;	// interlace		else			lof <= 1;reg	 xln;		//extra line (used in interlaced mode)always @(posedge clk)	if (eol)		if (lof && vpos==vtotal)			xln <= 1;		else			xln <= 0;			//generate end of frame signalassign eof = (eol && vpos==vtotal && !lof) || (eol && xln && lof);//vertical sync and vertical blankingalways @(posedge clk)	if ((vpos==vsstrt && hpos==hsstrt && !lof) || (vpos==vsstrt && hpos==hcenter && lof))		_vsync <= 0;	else if ((vpos==vsstop && hpos==hcenter && !lof) || (vpos==vsstop+1 && hpos==hsstrt && lof))		_vsync <= 1;//vertical blanking end (last line)assign vblend = vpos==vbstop ? 1 : 0;assign vblank = vpos <= vbstop ? 1: 0;//vbl output for sprite engineassign vbl = vblank;//--------------------------------------------------------------------------------------//composite blankingassign blank = hblank;//--------------------------------------------------------------------------------------endmodule