86 lines
2.4 KiB
C
86 lines
2.4 KiB
C
/*
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* Copyright © 1999 Keith Packard
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*
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* Permission to use, copy, modify, distribute, and sell this software and its
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* documentation for any purpose is hereby granted without fee, provided that
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* the above copyright notice appear in all copies and that both that
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* copyright notice and this permission notice appear in supporting
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* documentation, and that the name of Keith Packard not be used in
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* advertising or publicity pertaining to distribution of the software without
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* specific, written prior permission. Keith Packard makes no
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* representations about the suitability of this software for any purpose. It
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* is provided "as is" without express or implied warranty.
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*
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* KEITH PACKARD DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
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* INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
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* EVENT SHALL KEITH PACKARD BE LIABLE FOR ANY SPECIAL, INDIRECT OR
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* CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
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* DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
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* TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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* PERFORMANCE OF THIS SOFTWARE.
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*/
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#ifdef HAVE_CONFIG_H
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#include <kdrive-config.h>
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#endif
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#include "s3.h"
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/*
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* Clock synthesis:
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*
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* f_out = f_ref * ((M + 2) / ((N + 2) * (1 << R)))
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*
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* Constraints:
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*
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* 1. 135MHz <= f_ref * ((M + 2) / (N + 2)) <= 270 MHz
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* 2. N >= 1
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*
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* Vertical refresh rate = clock / ((hsize + hblank) * (vsize + vblank))
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* Horizontal refresh rate = clock / (hsize + hblank)
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*/
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/* all in kHz */
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#define MIN_VCO 180000.0
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#define MAX_VCO 360000.0
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void
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s3GetClock (int target, int *Mp, int *Np, int *Rp, int maxM, int maxN, int maxR)
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{
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int M, N, R, bestM, bestN;
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int f_vco, f_out;
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int err, abserr, besterr;
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/*
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* Compute correct R value to keep VCO in range
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*/
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for (R = 0; R <= maxR; R++)
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{
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f_vco = target * (1 << R);
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if (MIN_VCO <= f_vco && f_vco < MAX_VCO)
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break;
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}
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/* M = f_out / f_ref * ((N + 2) * (1 << R)); */
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besterr = target;
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for (N = 0; N <= maxN; N++)
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{
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M = (target * (N + 2) * (1 << R) + (S3_CLOCK_REF/2)) / S3_CLOCK_REF - 2;
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if (0 <= M && M <= maxM)
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{
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f_out = S3_CLOCK(M,N,R);
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err = target - f_out;
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if (err < 0)
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err = -err;
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if (err < besterr)
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{
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besterr = err;
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bestM = M;
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bestN = N;
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}
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}
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}
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*Mp = bestM;
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*Np = bestN;
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*Rp = R;
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}
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