xsrc/xfree/xc/programs/Xserver/hw/tinyx/trio/s3clock.c

/*
 * Copyright © 1999 Keith Packard
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that
 * copyright notice and this permission notice appear in supporting
 * documentation, and that the name of Keith Packard not be used in
 * advertising or publicity pertaining to distribution of the software without
 * specific, written prior permission.  Keith Packard makes no
 * representations about the suitability of this software for any purpose.  It
 * is provided "as is" without express or implied warranty.
 *
 * KEITH PACKARD DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL KEITH PACKARD BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */
/* $XFree86: xc/programs/Xserver/hw/tinyx/trio/s3clock.c,v 1.1 2004/06/02 22:43:03 dawes Exp $ */
/*
 * Copyright (c) 2004 by The XFree86 Project, Inc.
 * All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject
 * to the following conditions:
 *
 *   1.  Redistributions of source code must retain the above copyright
 *       notice, this list of conditions, and the following disclaimer.
 *
 *   2.  Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer
 *       in the documentation and/or other materials provided with the
 *       distribution, and in the same place and form as other copyright,
 *       license and disclaimer information.
 *
 *   3.  The end-user documentation included with the redistribution,
 *       if any, must include the following acknowledgment: "This product
 *       includes software developed by The XFree86 Project, Inc
 *       (http://www.xfree86.org/) and its contributors", in the same
 *       place and form as other third-party acknowledgments.  Alternately,
 *       this acknowledgment may appear in the software itself, in the
 *       same form and location as other such third-party acknowledgments.
 *
 *   4.  Except as contained in this notice, the name of The XFree86
 *       Project, Inc shall not be used in advertising or otherwise to
 *       promote the sale, use or other dealings in this Software without
 *       prior written authorization from The XFree86 Project, Inc.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE XFREE86 PROJECT, INC OR ITS 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.
 */

#include "s3.h"

/*
 * Clock synthesis:
 *
 *  f_out = f_ref * ((M + 2) / ((N + 2) * (1 << R)))
 *
 *  Constraints:
 *
 *  1.	135MHz <= f_ref * ((M + 2) / (N + 2)) <= 270 MHz
 *  2.	N >= 1
 *
 *  Vertical refresh rate = clock / ((hsize + hblank) * (vsize + vblank))
 *  Horizontal refresh rate = clock / (hsize + hblank)
 */
 
/* all in kHz */
#define MIN_VCO	180000.0
#define MAX_VCO 360000.0

void
s3GetClock (int target, int *Mp, int *Np, int *Rp, int maxM, int maxN, int maxR)
{
    int	    M, N, R, bestM = 0, bestN = 0;
    int	    f_vco, f_out;
    int	    err, besterr;

    /*
     * Compute correct R value to keep VCO in range
     */
    for (R = 0; R <= maxR; R++)
    {
	f_vco = target * (1 << R);
	if (MIN_VCO <= f_vco && f_vco < MAX_VCO)
	    break;
    }

    /* M = f_out / f_ref * ((N + 2) * (1 << R)); */
    besterr = target;
    for (N = 0; N <= maxN; N++)
    {
	M = (target * (N + 2) * (1 << R) + (S3_CLOCK_REF/2)) / S3_CLOCK_REF - 2;
	if (0 <= M && M <= maxM)
	{
	    f_out = S3_CLOCK(M,N,R);
	    err = target - f_out;
	    if (err < 0)
		err = -err;
	    if (err < besterr)
	    {
		besterr = err;
		bestM = M;
		bestN = N;
	    }
	}
    }
    *Mp = bestM;
    *Np = bestN;
    *Rp = R;
}