/* watch.c - poll randseed via /dev/mem without forking; timestamp changes */
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>
#include <inttypes.h>

#define KERNBASE 0xFFFFFFFF80000000ULL

int main(int argc, char **argv)
{
    int secs = argc > 1 ? atoi(argv[1]) : 15;
    int fd = open("/dev/mem", O_RDONLY);
    if (fd < 0) { perror("open"); return 1; }
    off_t phys = 0x81124c00; /* randseed */
    uint64_t prev = 0, cur;
    struct timespec ts;
    struct timespec t0;
    clock_gettime(CLOCK_MONOTONIC, &t0);
    if (pread(fd, &prev, 8, phys) != 8) { perror("pread"); return 1; }
    for (;;) {
        clock_gettime(CLOCK_MONOTONIC, &ts);
        double el = (ts.tv_sec - t0.tv_sec) + 1e-9*(ts.tv_nsec - t0.tv_nsec);
        if (el > secs) break;
        if (pread(fd, &cur, 8, phys) != 8) { perror("pread"); return 1; }
        if (cur != prev) {
            printf("%9.6f 0x%llx\n", el, (unsigned long long)cur);
            fflush(stdout);
            prev = cur;
        }
    }
    return 0;
}