--- ski-1.3.2/src/itc.c.~1~	2014-01-27 12:51:31.790027146 +0100
+++ ski-1.3.2/src/itc.c	2014-01-28 10:29:07.082920979 +0100
@@ -11,6 +11,9 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
 #include "itc.h"
 
 static unsigned long long itm;
@@ -18,10 +21,23 @@ static unsigned long long itc;
 static struct timeval tv;
 static int itimer_active;
 char itc_itimer_fired;
+int itc_onalrm_do_write;
+int itc_onalrm_read_fd = -1;
+static int itc_onalrm_write_fd = -1;
 
 static void onalrm(int sig)
 {
     itc_itimer_fired = 1;
+
+    if (itc_onalrm_do_write) {
+	int oerrno;
+	char c;
+
+	oerrno = errno;
+	c = 0;
+	write(itc_onalrm_write_fd, &c, 1);
+	errno = oerrno;
+    }
 }
 
 static void itimer_stop(void)
@@ -44,7 +60,7 @@ static void itimer_start(void)
 {
     unsigned long long ticks, usecs, seconds;
     struct itimerval itv;
-    static int catch_sigalrm_done;
+    static int init_done;
 
     itc_itimer_fired = 0;
 
@@ -69,10 +85,29 @@ static void itimer_start(void)
     itv.it_interval.tv_sec = 0;
     itv.it_interval.tv_usec = 0;
 
-    if (!catch_sigalrm_done) {
+    if (!init_done) {
+	int pipefd[2];
+	int i;
 	struct sigaction act;
 
-	catch_sigalrm_done = 1;
+	if (pipe(pipefd) == -1) {
+	    perror("pipe");
+	    exit(1);
+	}
+
+	for (i = 0; i < 2; ++i) {
+	    int flags;
+
+	    flags = fcntl(pipefd[i], F_GETFL);
+	    if (flags == -1
+		|| fcntl(pipefd[i], F_SETFL, flags | O_NONBLOCK) == -1) {
+		perror("fcntl");
+		exit(1);
+	    }
+	}
+
+	itc_onalrm_write_fd = pipefd[1];
+	itc_onalrm_read_fd = pipefd[0];
 
 	memset(&act, 0, sizeof act);
 	act.sa_handler = onalrm;
@@ -81,6 +116,8 @@ static void itimer_start(void)
 	    perror("sigaction");
 	    exit(1);
 	}
+
+	init_done = 1;
     }
 
     itimer_active = 1;
--- ski-1.3.2/src/itc.h.~1~	2014-01-27 12:51:31.790027146 +0100
+++ ski-1.3.2/src/itc.h	2014-01-27 14:10:38.311831156 +0100
@@ -16,4 +16,7 @@ static __inline__ int itc_tick_overflow(
     return 1;
 }
 
+extern int itc_onalrm_do_write;
+extern int itc_onalrm_read_fd;
+
 #endif	/* _SKI_ITC_H */
--- ski-1.3.2/src/linux/syscall-linux.c.~1~	2014-01-27 12:51:58.660109271 +0100
+++ ski-1.3.2/src/linux/syscall-linux.c	2014-01-28 11:19:41.950285562 +0100
@@ -93,6 +93,7 @@
 #include "interruption.h"
 #include "netdev.h"
 #include "os_support.h"
+#include "itc.h"
 
 #if defined NEW_MP
 # error "not supported"
@@ -4360,6 +4361,68 @@ asynckb (int sig)
 
 #endif
 
+/*
+ * Sleep until SIGIO or SIGALRM is received; this relies on
+ * keyboard/ethernet input being detected via SIGIO, and the
+ * ITC now being emulated via setitimer() and SIGALRM.
+ *
+ * A SIGALRM might be delivered just before we enter the
+ * blocking (but interruptible) system call.  To ensure that
+ * we notice that SIGALRM, the protocol is:
+ *
+ * 1. We set the itc_onalrm_do_write flag to non-zero.
+ *    This informs the ITC SIGALRM handler that it should also
+ *    write a dummy byte to itc_onalrm_write_fd -- the write
+ *    end of a pipe whose read end is itc_onalrm_read_fd.
+ *    (This flag is an optimization, to avoid forcing every
+ *    ITC SIGLARM to write to the pipe.)
+ *
+ * 2. We check if an ITC SIGALRM has been received, if so we
+ *    clear itc_onalrm_do_write and don't sleep.
+ *
+ * 3. We call select on itc_onalrm_read_fd in a loop until
+ *    it returns success or a non-EINTR errno.
+ *
+ * 4. We clear the itc_onalrm_do_write flag.
+ *
+ * 5. We empty the pipe.
+ *
+ * Any SIGALRM before step 2 is detected by step 2, and any SIGALRM
+ * after step 2 is detected via the pipe by step 3.
+ */
+static void
+doSSC_HALT_LIGHT (void)
+{
+    fd_set readfds;
+    int ret;
+
+    if (itc_onalrm_read_fd < 0)
+	return;
+
+    FD_ZERO (&readfds);
+    FD_SET (itc_onalrm_read_fd, &readfds);
+
+    itc_onalrm_do_write = 1;
+
+    if (itc_itimer_fired) {
+	itc_onalrm_do_write = 0;
+	return;
+    }
+
+    do {
+	ret = select (itc_onalrm_read_fd + 1, &readfds, NULL, NULL, NULL);
+    } while (ret == -1 && errno == EINTR);
+
+    itc_onalrm_do_write = 0;
+
+    if (ret != -1 && FD_ISSET (itc_onalrm_read_fd, &readfds)) {
+	char c;
+
+	while (read(itc_onalrm_read_fd, &c, 1) != -1)
+	    ;
+    }
+}
+
 void
 doSSC (HWORD num, REG arg0, REG arg1, REG arg2, REG arg3, REG *ret)
 {
@@ -4389,6 +4452,10 @@ doSSC (HWORD num, REG arg0, REG arg1, RE
       progStop ("SSC breakpoint\n");
       break;
 
+    case SSC_HALT_LIGHT:
+      doSSC_HALT_LIGHT ();
+      break;
+
     case SSC_CTL_TRACE:
 #ifdef TRACE_DAVIDM
       {
--- ski-1.3.2/src/ssc.h.~1~	2008-02-05 05:11:38.000000000 +0100
+++ ski-1.3.2/src/ssc.h	2014-01-27 12:52:12.250151160 +0100
@@ -28,6 +28,7 @@
 
 #define SSC_STOP			 0
 
+#define SSC_HALT_LIGHT			19
 #define SSC_CONSOLE_INIT		20
 #define SSC_GETCHAR			21
 #define SSC_PUTCHAR			31