diff --git a/ski-bootloader/boot_head.S b/ski-bootloader/boot_head.S
index 5931117..9499fb9 100644
--- a/ski-bootloader/boot_head.S
+++ b/ski-bootloader/boot_head.S
@@ -5,6 +5,10 @@
  */
 
 #include <ia64/pal.h>
+#ifndef __ASSEMBLY__
+#define __ASSEMBLY__
+#endif
+#include "ssc.h"
 
 #define ENTRY(name)		\
 	.align 32;		\
@@ -157,6 +161,11 @@ static:	cmp.eq p6,p7=PAL_PTCE_INFO,r28
 	mov	r8=0			/* status = 0 */
 	mov	r9=0x80|0x01		/* NatPage|WB */
 	;;
+1:	cmp.eq p6,p7=PAL_HALT_LIGHT,r28
+(p7)	br.cond.sptk.few 1f
+	mov	r15=SSC_HALT_LIGHT
+	break	0x80001
+	;;
 1:	br.cond.sptk.few rp
 stacked:
 	br.ret.sptk.few rp
diff --git a/ski-bootloader/include/ia64/pal.h b/ski-bootloader/include/ia64/pal.h
index 048060c..95f8911 100644
--- a/ski-bootloader/include/ia64/pal.h
+++ b/ski-bootloader/include/ia64/pal.h
@@ -8,5 +8,6 @@
 #define PAL_FREQ_RATIOS		14
 #define PAL_PERF_MON_INFO	15
 #define PAL_RSE_INFO		19
+#define PAL_HALT_LIGHT		29	/* enter the low power light halt state */
 
 #endif /* _INCLUDE_PAL_H_ */
diff --git a/ski-bootloader/ssc.h b/ski-bootloader/ssc.h
index 7ce12cc..a3a0c06 100644
--- a/ski-bootloader/ssc.h
+++ b/ski-bootloader/ssc.h
@@ -9,6 +9,7 @@
 
 /* Simulator system calls: */
 
+#define SSC_HALT_LIGHT			19
 #define SSC_CONSOLE_INIT		20
 #define SSC_GETCHAR			21
 #define SSC_PUTCHAR			31
@@ -28,9 +29,13 @@
 #define SSC_GET_ARGS			75
 #define SSC_GET_INITRAMFS		77
 
+#ifndef __ASSEMBLY__
+
 /*
  * Simulator system call.
  */
 extern long ssc (long arg0, long arg1, long arg2, long arg3, int nr);
 
+#endif /* !__ASSEMBLY */
+
 #endif /* ssc_h */
diff --git a/ski-efi/boot_head.S b/ski-efi/boot_head.S
index 5931117..9499fb9 100644
--- a/ski-efi/boot_head.S
+++ b/ski-efi/boot_head.S
@@ -5,6 +5,10 @@
  */
 
 #include <ia64/pal.h>
+#ifndef __ASSEMBLY__
+#define __ASSEMBLY__
+#endif
+#include "ssc.h"
 
 #define ENTRY(name)		\
 	.align 32;		\
@@ -157,6 +161,11 @@ static:	cmp.eq p6,p7=PAL_PTCE_INFO,r28
 	mov	r8=0			/* status = 0 */
 	mov	r9=0x80|0x01		/* NatPage|WB */
 	;;
+1:	cmp.eq p6,p7=PAL_HALT_LIGHT,r28
+(p7)	br.cond.sptk.few 1f
+	mov	r15=SSC_HALT_LIGHT
+	break	0x80001
+	;;
 1:	br.cond.sptk.few rp
 stacked:
 	br.ret.sptk.few rp
diff --git a/ski-efi/include/ia64/pal.h b/ski-efi/include/ia64/pal.h
index 048060c..95f8911 100644
--- a/ski-efi/include/ia64/pal.h
+++ b/ski-efi/include/ia64/pal.h
@@ -8,5 +8,6 @@
 #define PAL_FREQ_RATIOS		14
 #define PAL_PERF_MON_INFO	15
 #define PAL_RSE_INFO		19
+#define PAL_HALT_LIGHT		29	/* enter the low power light halt state */
 
 #endif /* _INCLUDE_PAL_H_ */
diff --git a/ski-efi/ssc.h b/ski-efi/ssc.h
index 7ce12cc..a3a0c06 100644
--- a/ski-efi/ssc.h
+++ b/ski-efi/ssc.h
@@ -9,6 +9,7 @@
 
 /* Simulator system calls: */
 
+#define SSC_HALT_LIGHT			19
 #define SSC_CONSOLE_INIT		20
 #define SSC_GETCHAR			21
 #define SSC_PUTCHAR			31
@@ -28,9 +29,13 @@
 #define SSC_GET_ARGS			75
 #define SSC_GET_INITRAMFS		77
 
+#ifndef __ASSEMBLY__
+
 /*
  * Simulator system call.
  */
 extern long ssc (long arg0, long arg1, long arg2, long arg3, int nr);
 
+#endif /* !__ASSEMBLY */
+
 #endif /* ssc_h */
diff --git a/src/linux/syscall-linux.c b/src/linux/syscall-linux.c
index 9f4fe1a..0b12011 100644
--- a/src/linux/syscall-linux.c
+++ b/src/linux/syscall-linux.c
@@ -95,6 +95,7 @@
 #include "os_support.h"
 #include "syscall_api.h"
 #include "ui.h"
+#include "itc.h"
 
 #if defined NEW_MP
 # error "not supported"
@@ -4501,6 +4502,50 @@ 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 atomically retrieve the current signal mask and block SIGALRM.
+ *
+ * 2. We check if an ITC SIGALRM has been received, if so we
+ *    restore the signal mask and return.
+ *
+ * 3. We call pselect to atomically unblock SIGALRM and block until
+ *    a signal is delivered.
+ *
+ * 4. We unblock SIGALRM since pselect re-blocks it.
+ *
+ * Any SIGALRM before step 1 is detected by step 2, and any SIGALRM
+ * after step 1 is detected via the pselect in step 3.
+ */
+static void
+doSSC_HALT_LIGHT (void)
+{
+    sigset_t set, oldset;
+
+    sigemptyset(&set);
+    sigaddset(&set, SIGALRM);
+
+    if (sigprocmask(SIG_BLOCK, &set, &oldset) == -1) {
+	perror("sigprocmask");
+	exit(1);
+    }
+
+    if (itc_itimer_fired) {
+	sigprocmask(SIG_SETMASK, &oldset, NULL);
+	return;
+    }
+
+    pselect (0, NULL, NULL, NULL, NULL, &oldset);
+    sigprocmask(SIG_SETMASK, &oldset, NULL);
+}
+
 void
 doSSC (HWORD num, REG arg0, REG arg1, REG arg2, REG arg3, REG *ret)
 {
@@ -4530,6 +4575,10 @@ doSSC (HWORD num, REG arg0, REG arg1, REG arg2, REG arg3, REG *ret)
       progStop ("SSC breakpoint\n");
       break;
 
+    case SSC_HALT_LIGHT:
+      doSSC_HALT_LIGHT ();
+      break;
+
     case SSC_CTL_TRACE:
 #ifdef TRACE_DAVIDM
       {
diff --git a/src/ssc.h b/src/ssc.h
index 077c8b2..96ac2a1 100644
--- a/src/ssc.h
+++ b/src/ssc.h
@@ -30,6 +30,7 @@
 
 #define SSC_STOP			 0
 
+#define SSC_HALT_LIGHT			19
 #define SSC_CONSOLE_INIT		20
 #define SSC_GETCHAR			21
 #define SSC_PUTCHAR			31