xserver-multidpi/hw/kdrive/savage/s3clock.c

/*
 * Id: s3clock.c,v 1.2 1999/11/02 06:16:29 keithp Exp $
 *
 * Copyright 1999 SuSE, Inc.
 *
 * 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 SuSE not be used in advertising or
 * publicity pertaining to distribution of the software without specific,
 * written prior permission.  SuSE makes no representations about the
 * suitability of this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 *
 * SuSE DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL SuSE
 * 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.
 *
 * Author:  Keith Packard, SuSE, Inc.
 */
/* $XFree86: xc/programs/Xserver/hw/kdrive/savage/s3clock.c,v 1.3 2000/02/23 20:30:02 dawes Exp $ */

#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 */

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

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

    /* M = f_out / f_ref * ((N + 2) * (1 << R)); */
    besterr = target;
    for (N = 1; N <= maxN; N++)
    {
	M = ((target * (N + 2) * (1 << R) + (S3_CLOCK_REF/2)) + 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;
}