1 files changed, 89 insertions, 0 deletions
diff --git a/hw/kdrive/trio/s3clock.c b/hw/kdrive/trio/s3clock.c
new file mode 100644
index 000000000..1c4f893dd
--- /dev/null
+++ b/hw/kdrive/trio/s3clock.c
@@ -0,0 +1,89 @@
+/*
+ * $Id$
+ *
+ * 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: $ */
+
+#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 (S3Timing *t, int *Mp, int *Np, int *Rp, int maxM, int maxN, int maxR)
+{
+    int	    M, N, R, bestM, bestN;
+    int	    f_vco, f_out;
+    int	    target;
+    int	    err, abserr, besterr;
+
+    target = ((t->horizontal + t->hblank) * 
+	      (t->vertical + t->vblank) * 
+	      t->rate) / 1000;
+    /*
+     * 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;
+}