ref: 41d4cecf6d55af3ee0ced4c45d34450f4501608b
dir: /sys/src/cmd/aux/vga/tvp3026clock.c/
#include <u.h>
#include <libc.h>
#include <bio.h>
#include "pci.h"
#include "vga.h"
#define SCALE(f) ((f)/10) /* could be /10 */
static void
init(Vga* vga, Ctlr* ctlr)
{
int f, k;
ulong fmin, fvco, m, n, p, q;
double z;
if(ctlr->flag & Finit)
return;
if(vga->f[0] == 0)
vga->f[0] = vga->mode->frequency;
vga->misc &= ~0x0C;
if(vga->f[0] == VgaFreq0){
/* nothing to do */;
}
else if(vga->f[0] == VgaFreq1)
vga->misc |= 0x04;
else
vga->misc |= 0x0C;
/*
* Look for values of n, d and p that give
* the least error for
* Fvco = 8*RefFreq*(65-m)/(65-n)
* Fpll = Fvco/2**p
* N and m are 6 bits, p is 2 bits. Constraints:
* 110MHz <= Fvco <= 250MHz
* 40 <= n <= 62
* 1 <= m <= 62
* 0 <= p <= 3
* Should try to minimise n, m.
*
* There's nothing like brute force and ignorance.
*/
fmin = vga->f[0];
vga->m[0] = 0x15;
vga->n[0] = 0x18;
vga->p[0] = 3;
for(m = 62; m > 0; m--){
for(n = 62; n >= 40; n--){
fvco = 8*SCALE(RefFreq)*(65-m)/(65-n);
if(fvco < SCALE(110000000) || fvco > SCALE(250000000))
continue;
for(p = 0; p < 4; p++){
f = SCALE(vga->f[0]) - (fvco>>p);
if(f < 0)
f = -f;
if(f < fmin){
fmin = f;
vga->m[0] = m;
vga->n[0] = n;
vga->p[0] = p;
}
}
}
}
/*
* Now the loop clock:
* m is fixed;
* calculate n;
* set z to the lower bound (110MHz) and calculate p and q.
*/
vga->m[1] = 61;
if(ctlr->flag & Uenhanced)
k = 64/8;
else
k = 8/8;
n = 65 - 4*k;
fvco = (8*RefFreq*(65-vga->m[0]))/(65-vga->n[0]);
vga->f[1] = fvco;
z = 110.0*(65-n)/(4*(fvco/1000000.0)*k);
if(z <= 16){
for(p = 0; p < 4; p++){
if(1<<(p+1) > z)
break;
}
q = 0;
}
else{
p = 3;
q = (z - 16)/16 + 1;
}
vga->n[1] = n;
vga->p[1] = p;
vga->q[1] = q;
ctlr->flag |= Finit;
}
Ctlr tvp3026clock = {
"tvp3026clock", /* name */
0, /* snarf */
0, /* options */
init, /* init */
0, /* load */
0, /* dump */
};