Subversion Repositories planix.SVN

#include <u.h>
#include <libc.h>
#include <bio.h>

#include "pci.h"
#include "vga.h"

#define SCALE(f)        ((f)/1)         /* could be /10 */

static void
init(Vga* vga, Ctlr* ctlr)
{
        int f;
        ulong d, dmax, fmin, fvco, n, nmax, p;

        if(ctlr->flag & Finit)
                return;

        if(vga->f[0] == 0)
                vga->f[0] = vga->mode->frequency;

        /*
         * Look for values of n, d and p that give
         * the least error for
         *      Fvco = RefFreq*((n+2)*8)/(d+2)
         *      Fpll = Fvco/2**p
         * N and d are 7-bits, p is 2-bits. Constraints:
         *      RefFreq/(n+2) > 1MHz
         *      110MHz <= Fvco <= 220MHz
         *      n, d >= 1
         * Should try to minimise n, d.
         *
         * There's nothing like brute force and ignorance.
         */
        fmin = vga->f[0];
        vga->d[0] = 6;
        vga->n[0] = 5;
        vga->p[0] = 2;
        dmax = (RefFreq/1000000)-2;
        for(d = 1; d < dmax; d++){
                /*
                 * Calculate an upper bound on n
                 * to satisfy the condition
                 *      Fvco <= 220MHz
                 * This will hopefully prevent arithmetic
                 * overflow.
                 */
                nmax = ((220000000+RefFreq)*(d+2))/(RefFreq*8) - 2;
                for(n = 1; n < nmax; n++){
                        fvco = SCALE(RefFreq)*((n+2)*8)/(d+2);
                        if(fvco < SCALE(110000000) || fvco > SCALE(220000000))
                                continue;
                        for(p = 1; p < 4; p++){
                                f = SCALE(vga->f[0]) - (fvco>>p);
                                if(f < 0)
                                        f = -f;
                                if(f < fmin){
                                        fmin = f;
                                        vga->d[0] = d;
                                        vga->n[0] = n;
                                        vga->p[0] = p;
                                }
                        }
                }
        }

        ctlr->flag |= Finit;
}

Ctlr tvp3025clock = {
        "tvp3025clock",                 /* name */
        0,                              /* snarf */
        0,                              /* options */
        init,                           /* init */
        0,                              /* load */
        0,                              /* dump */
};