imx233_audioout_freq.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

long nearest_freq(int freq, int mult, int hold, int *p_int, int *p_frac)
{
    uint64_t num = 750000 ;
    num *= mult << 13;
    num /= freq * (hold + 1);
    *p_int = num / (1 << 13);
    *p_frac = num % (1 << 13);

    num = 750000;
    num *= (1 << 13) * mult;
    num /= (*p_frac + (*p_int << 13)) * (hold + 1);
    return num;
}

void best(long f)
{
    long best_error = f;
    long best_base_mult = 1;
    long best_src_hold = 0;
    for(int base_mult = 1; base_mult <= 4; base_mult *= 2)
    {
        printf("[base_mult = %d]\n", base_mult);
        for(int src_hold = 0; src_hold < 8; src_hold++)
        {
            printf("  [src_hold = %d]\n", src_hold);
            int src_int, src_frac;
            long cf = nearest_freq(f, base_mult, src_hold, &src_int, &src_frac);
            printf("    src=[%d, %d] cf = %ld Hz  err = %d Hz\n",
                src_int, src_frac, cf, abs(cf - f));
        }
    }
}

int main(int argc, char **argv)
{
    if(argc != 2)
        return 1;
    long f = strtol(argv[1], NULL, 0);
    
    printf("freq = %ld Hz\n", f);

    int base_mult = 1;
    int src_hold = 0;
    if(f > 96000)
        base_mult = 4;
    else if(f > 48000)
        base_mult = 2;
    else if(f <= 12000)
        src_hold = 3;
    else if(f <= 24000)
        src_hold = 1;

    int src_int = (750000 * base_mult) / (f * (src_hold + 1));
    int src_frac = ((750000 * base_mult - src_int * f * (src_hold + 1)) << 13) / (f * (src_hold + 1));

    int res_f = ((750000LL << 13LL) * base_mult) / (((src_int << 13) + src_frac) * (src_hold + 1));
    
    printf("base_mult = %d  src_hold = %d  src_int = %d  src_frac = %d\n",
        base_mult, src_hold, src_int, src_frac);
    printf("result freq = %d  error = %d\n", res_f, abs(res_f - f));

    return 0;
}