ref: 50791b875552b0dc5748aa67c95776736f6ff4b7
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 */ };