diff --git a/hw/acpi/Makefile.objs b/hw/acpi/Makefile.objs
index a0b63b5626..951ea5af77 100644
--- a/hw/acpi/Makefile.objs
+++ b/hw/acpi/Makefile.objs
@@ -1,2 +1,2 @@
-common-obj-$(CONFIG_ACPI) += core.o piix4.o ich9.o
+obj-$(CONFIG_ACPI) += core.o piix4.o ich9.o
 
diff --git a/hw/acpi/core.c b/hw/acpi/core.c
index 58308a3406..13e010bc71 100644
--- a/hw/acpi/core.c
+++ b/hw/acpi/core.c
@@ -482,13 +482,21 @@ void acpi_pm_tmr_update(ACPIREGS *ar, bool enable)
 void acpi_pm_tmr_calc_overflow_time(ACPIREGS *ar)
 {
     int64_t d = acpi_pm_tmr_get_clock();
+#ifdef TARGET_XBOX
+    ar->tmr.overflow_time = (d + 0x80000000LL) & ~0x7fffffffLL;
+#else
     ar->tmr.overflow_time = (d + 0x800000LL) & ~0x7fffffLL;
+#endif
 }
 
 static uint32_t acpi_pm_tmr_get(ACPIREGS *ar)
 {
     uint32_t d = acpi_pm_tmr_get_clock();
+#ifdef TARGET_XBOX
+    return d & 0xffffffff;
+#else
     return d & 0xffffff;
+#endif
 }
 
 static void acpi_pm_tmr_timer(void *opaque)
diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index 8988047ace..b2110fa9c7 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -492,6 +492,9 @@ static void fadt_setup(AcpiFadtDescriptorRev1 *fadt, AcpiPmInfo *pm)
                               (1 << ACPI_FADT_F_SLP_BUTTON) |
                               (1 << ACPI_FADT_F_RTC_S4));
     fadt->flags |= cpu_to_le32(1 << ACPI_FADT_F_USE_PLATFORM_CLOCK);
+#ifdef TARGET_XBOX
+    fadt->flags |= cpu_to_le32(1 << ACPI_FADT_F_TMR_VAL_EXT);
+#endif
 }
 
 
diff --git a/hw/xbox/acpi_xbox.c b/hw/xbox/acpi_xbox.c
index 0648c65edb..ea138bd9da 100644
--- a/hw/xbox/acpi_xbox.c
+++ b/hw/xbox/acpi_xbox.c
@@ -72,10 +72,29 @@ static const MemoryRegionOps xbox_pm_gpio_ops = {
     .write = xbox_pm_gpio_write,
 };
 
+static void pm_update_sci(XBOX_PMRegs *pm)
+{
+    int sci_level, pm1a_sts;
+
+    pm1a_sts = acpi_pm1_evt_get_sts(&pm->acpi_regs);
+
+    sci_level = (((pm1a_sts & pm->acpi_regs.pm1.evt.en) &
+                  (ACPI_BITMASK_RT_CLOCK_ENABLE |
+                   ACPI_BITMASK_POWER_BUTTON_ENABLE |
+                   ACPI_BITMASK_GLOBAL_LOCK_ENABLE |
+                   ACPI_BITMASK_TIMER_ENABLE)) != 0);
+    qemu_set_irq(pm->irq, sci_level);
+
+    /* schedule a timer interruption if needed */
+    acpi_pm_tmr_update(&pm->acpi_regs,
+                       (pm->acpi_regs.pm1.evt.en & ACPI_BITMASK_TIMER_ENABLE) &&
+                       !(pm1a_sts & ACPI_BITMASK_TIMER_STATUS));
+}
+
 static void xbox_pm_update_sci_fn(ACPIREGS *regs)
 {
-    //XBOX_PMRegs *pm = container_of(regs, XBOX_PMRegs, acpi_regs);
-    //pm_update_sci(pm);
+    XBOX_PMRegs *pm = container_of(regs, XBOX_PMRegs, acpi_regs);
+    pm_update_sci(pm);
 }
 
 #define XBOX_PM_BASE_BAR 0
diff --git a/include/hw/acpi/acpi.h b/include/hw/acpi/acpi.h
index 6bbcb1750d..4ccaf17887 100644
--- a/include/hw/acpi/acpi.h
+++ b/include/hw/acpi/acpi.h
@@ -34,7 +34,11 @@
 #define ACPI_PM_TIMER_WIDTH             32
 
 /* PM Timer ticks per second (HZ) */
+#ifdef TARGET_XBOX
+#define PM_TIMER_FREQUENCY  3375000
+#else
 #define PM_TIMER_FREQUENCY  3579545
+#endif
 
 
 /* ACPI fixed hardware registers */