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/*
* Id: s3clock.c,v 1.1 1999/11/02 08:17:24 keithp Exp $
*
* 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.
*/
/* $RCSId: xc/programs/Xserver/hw/kdrive/trio/s3clock.c,v 1.2 1999/12/30 03:03:19 robin 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 */
#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, 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 (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;
}
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