#include <sys/time.h>
#include <signal.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>

#ifndef SA_RESTART
#define SA_RESTART 0
#endif

unsigned jiffies;
static sigset_t posix_signal_mask;

static void
clock_start(int us)
	{
	struct itimerval new_it;

	new_it.it_value.tv_sec = 0;
	new_it.it_value.tv_usec = us;
	new_it.it_interval.tv_sec = 0;
	new_it.it_interval.tv_usec = us;
	setitimer(ITIMER_REAL, &new_it, 0);
	}

static void
isr_enable(unsigned level)
	{
	if (level == 0)
		{
		sigprocmask(SIG_UNBLOCK, &posix_signal_mask, 0);
		}
	else
		{
		sigprocmask(SIG_BLOCK, &posix_signal_mask, 0);
		}
	}

static void
isr_handler(int sig_num)
	{
	switch(sig_num)
		{
		case SIGCHLD:
			break;
		case SIGALRM:
			++jiffies;
			break;
		default:
			break;
		}
	}

void
posix_init(void)
	{
	struct sigaction act;
	sigset_t mask;

	/*
	 * Block all the signals except SIGTRAP (for the debugger)
	 * and fatal error signals.
	 */
	sigfillset(&posix_signal_mask);
	sigdelset(&posix_signal_mask, SIGTRAP);
	sigdelset(&posix_signal_mask, SIGABRT);
#ifdef SIGIOT
	sigdelset(&posix_signal_mask, SIGIOT);
#endif
	sigdelset(&posix_signal_mask, SIGCONT);
	sigdelset(&posix_signal_mask, SIGSEGV);
	sigdelset(&posix_signal_mask, SIGBUS);
	sigdelset(&posix_signal_mask, SIGFPE);

	isr_enable(1);

	/* Unblock signals. */
	mask = posix_signal_mask;
	sigprocmask(SIG_UNBLOCK, &mask, 0);

	act.sa_handler = isr_handler;
	act.sa_mask = mask;
	act.sa_flags = SA_RESTART;

	sigaction(SIGHUP, &act, 0);
	sigaction(SIGINT, &act, 0);
	sigaction(SIGQUIT, &act, 0);
	sigaction(SIGILL, &act, 0);
#ifdef SIGEMT
	sigaction(SIGEMT, &act, 0);
#endif
	sigaction(SIGFPE, &act, 0);
	sigaction(SIGKILL, &act, 0);
	sigaction(SIGBUS, &act, 0);
	sigaction(SIGSEGV, &act, 0);
#ifdef SIGSYS
	sigaction(SIGSYS, &act, 0);
#endif
	sigaction(SIGPIPE, &act, 0);
	sigaction(SIGALRM, &act, 0);
	sigaction(SIGTERM, &act, 0);
	sigaction(SIGUSR1, &act, 0);
	sigaction(SIGUSR2, &act, 0);
	sigaction(SIGCHLD, &act, 0);
	sigaction(SIGCLD, &act, 0);
#ifdef SIGPWR
	sigaction(SIGPWR, &act, 0);
#endif
	sigaction(SIGVTALRM, &act, 0);
	sigaction(SIGPROF, &act, 0);
	sigaction(SIGIO, &act, 0);
	sigaction(SIGWINCH, &act, 0);
	sigaction(SIGSTOP, &act, 0);
	sigaction(SIGTTIN, &act, 0);
	sigaction(SIGTTOU, &act, 0);
	sigaction(SIGURG, &act, 0);
#ifdef SIGLOST
    sigaction(SIGLOST, &act, 0);
#endif

	clock_start(1000);
	}

int
main(int argc, char *argv[])
	{
	posix_init();

	while (jiffies < 3000);

	printf("Hit any key to quit...\n");
	while (1)
		{
		if (getchar() > 0)
			break;
		}
	return 0;
	}