diff --git a/scp.c b/scp.c
index ebcbf226..187d70d3 100644
--- a/scp.c
+++ b/scp.c
@@ -602,8 +602,34 @@ static DEBTAB sim_dflt_debug[] = {
   {0}
 };
 
-static UNIT sim_step_unit = { UDATA (&step_svc, 0, 0)  };
-static UNIT sim_expect_unit = { UDATA (&expect_svc, 0, 0)  };
+static const char *sim_int_step_description (DEVICE *dptr)
+{
+return "Step/Next facility";
+}
+
+static UNIT sim_step_unit = { UDATA (&step_svc, 0, 0) };
+DEVICE sim_step_dev = {
+    "INT-STEP", &sim_step_unit, NULL, NULL, 
+    1, 0, 0, 0, 0, 0, 
+    NULL, NULL, NULL, NULL, NULL, NULL, 
+    NULL, DEV_NOSAVE, 0, 
+    NULL, NULL, NULL, NULL, NULL, NULL,
+    sim_int_step_description};
+
+static const char *sim_int_expect_description (DEVICE *dptr)
+{
+return "Expect facility";
+}
+
+static UNIT sim_expect_unit = { UDATA (&expect_svc, 0, 0) };
+DEVICE sim_expect_dev = {
+    "INT-EXPECT", &sim_expect_unit, NULL, NULL, 
+    1, 0, 0, 0, 0, 0, 
+    NULL, NULL, NULL, NULL, NULL, NULL, 
+    NULL, DEV_NOSAVE, 0, 
+    NULL, NULL, NULL, NULL, NULL, NULL,
+    sim_int_expect_description};
+
 #if defined USE_INT64
 static const char *sim_si64 = "64b data";
 #else
@@ -2388,6 +2414,8 @@ sim_log = NULL;
 if (sim_emax <= 0)
     sim_emax = 1;
 sim_timer_init ();
+sim_register_internal_device (&sim_expect_dev);
+sim_register_internal_device (&sim_step_dev);
 
 if ((stat = sim_ttinit ()) != SCPE_OK) {
     fprintf (stderr, "Fatal terminal initialization error\n%s\n",
@@ -9403,12 +9431,12 @@ t_stat sim_register_internal_device (DEVICE *dptr)
 {
 uint32 i;
 
-for (i = 0; (sim_devices[i] != NULL); i++)
-    if (sim_devices[i] == dptr)
-        return SCPE_OK;
 for (i = 0; i < sim_internal_device_count; i++)
     if (sim_internal_devices[i] == dptr)
         return SCPE_OK;
+for (i = 0; (sim_devices[i] != NULL); i++)
+    if (sim_devices[i] == dptr)
+        return SCPE_OK;
 ++sim_internal_device_count;
 sim_internal_devices = (DEVICE **)realloc(sim_internal_devices, (sim_internal_device_count+1)*sizeof(*sim_internal_devices));
 sim_internal_devices[sim_internal_device_count-1] = dptr;
@@ -10419,11 +10447,15 @@ do {
         sim_interval = sim_clock_queue->time;
     else
         sim_interval = noqueue_time = NOQUEUE_WAIT;
-    sim_debug (SIM_DBG_EVENT, sim_dflt_dev, "Processing Event for %s\n", sim_uname (uptr));
     AIO_EVENT_BEGIN(uptr);
-    if (uptr->usecs_remaining)
+    if (uptr->usecs_remaining) {
+        sim_debug (SIM_DBG_EVENT, sim_dflt_dev, "Requeueing %s after %.0f usecs\n", sim_uname (uptr), uptr->usecs_remaining);
         reason = sim_timer_activate_after (uptr, uptr->usecs_remaining);
+        }
     else {
+        sim_debug (SIM_DBG_EVENT, sim_dflt_dev, "Processing Event for %s\n", sim_uname (uptr));
+        if (uptr->uname && ((*uptr->uname == '\0') || (*uptr->uname == ' ')))
+            reason = SCPE_OK;   /* do nothing breakpoint location */
         if (uptr->action != NULL)
             reason = uptr->action (uptr);
         else
@@ -10607,10 +10639,10 @@ AIO_CANCEL(uptr);
 AIO_UPDATE_QUEUE;
 if (sim_clock_queue == QUEUE_LIST_END)
     return SCPE_OK;
-sim_debug (SIM_DBG_EVENT, sim_dflt_dev, "Canceling Event for %s\n", sim_uname(uptr));
 UPDATE_SIM_TIME;                                        /* update sim time */
 if (!sim_is_active (uptr))
     return SCPE_OK;
+sim_debug (SIM_DBG_EVENT, sim_dflt_dev, "Canceling Event for %s\n", sim_uname(uptr));
 nptr = QUEUE_LIST_END;
 
 if (sim_clock_queue == uptr) {
diff --git a/sim_timer.c b/sim_timer.c
index ae8d77a5..f340fb47 100644
--- a/sim_timer.c
+++ b/sim_timer.c
@@ -1037,6 +1037,7 @@ for (tmr=0; tmr<=SIM_NTIMERS; tmr++) {
 sim_stop_unit.action = &sim_timer_stop_svc;
 SIM_INTERNAL_UNIT.flags = UNIT_IDLE;
 sim_register_internal_device (&sim_timer_dev);          /* Register Clock Assist device */
+sim_register_internal_device (&sim_throttle_dev);       /* Register Throttle Device */
 sim_throttle_unit.action = &sim_throt_svc;
 sim_register_clock_unit_tmr (&SIM_INTERNAL_UNIT, SIM_INTERNAL_CLK);
 sim_idle_enab = FALSE;                                  /* init idle off */
@@ -1670,7 +1671,6 @@ else {
         sim_throt_wait = sim_throt_val;
         }
     }
-sim_register_internal_device (&sim_throttle_dev);       /* Register Throttle Device */
 if (sim_throt_type == SIM_THROT_SPC)    /* Set initial value while correct one is determined */
     sim_throt_cps = (int32)((1000.0 * sim_throt_val) / (double)sim_throt_sleep_time);
 else
@@ -1974,7 +1974,7 @@ if ((stat == SCPE_OK)                               &&
         if (fabs(skew) > fabs(rtc_clock_skew_max[tmr]))
             rtc_clock_skew_max[tmr] = skew;
         }
-    /* First gather the queued events that are scheduled for now */
+    /* Gather any queued events which are scheduled for right now */
     do {
         cptr = sim_clock_cosched_queue[tmr];
         sim_clock_cosched_queue[tmr] = cptr->next;
@@ -1996,11 +1996,11 @@ if ((stat == SCPE_OK)                               &&
         cptr->cancel = NULL;
         cptr->time = 0;
         if (cptr->usecs_remaining) {
-            sim_debug (DBG_QUE, &sim_timer_dev, " remnant: %.0f - next %s after cosched interval: %d ticks\n", cptr->usecs_remaining, (sptr != QUEUE_LIST_END) ? sim_uname (sptr) : "", sim_cosched_interval[tmr]);
+            sim_debug (DBG_QUE, &sim_timer_dev, "Rescheduling %s after %.0f usecs %s%s\n", sim_uname (cptr), cptr->usecs_remaining, (sptr != QUEUE_LIST_END) ? "- next: " : "", (sptr != QUEUE_LIST_END) ? sim_uname (sptr) : "");
             sim_timer_activate_after (cptr, cptr->usecs_remaining);
             }
         else {
-            sim_debug (DBG_QUE, &sim_timer_dev, " - next %s after cosched interval: %d ticks\n", (sptr != QUEUE_LIST_END) ? sim_uname (sptr) : "", sim_cosched_interval[tmr]);
+            sim_debug (DBG_QUE, &sim_timer_dev, "Activating %s now %s%s\n", sim_uname (cptr), (sptr != QUEUE_LIST_END) ? "- next: " : "", (sptr != QUEUE_LIST_END) ? sim_uname (sptr) : "");
             _sim_activate (cptr, 0);
             }
         }
@@ -2501,12 +2501,13 @@ for (tmr=0; tmr<=SIM_NTIMERS; tmr++)
         }
 if (sim_is_active (uptr))                               /* already active? */
     return SCPE_OK;
-uptr->usecs_remaining = 0;
 if (usec_delay <= 0.0) {
-    sim_debug (DBG_TIM, &sim_timer_dev, "sim_timer_activate_after(%s, %.0f usecs) - invalid usec value\n", 
+    sim_debug (DBG_QUE, &sim_timer_dev, "sim_timer_activate_after(%s, %.0f usecs) - invalid usec value\n", 
                sim_uname(uptr), usec_delay);
+    uptr->usecs_remaining = 0.0;
     return SCPE_ARG;
     }
+uptr->usecs_remaining = 0.0;
 /* 
  * Handle long delays by aligning with the calibrated timer's calibration
  * activities.  Delays which would expire prior to the next calibration
@@ -2532,8 +2533,8 @@ if ((sim_calb_tmr != -1) && (rtc_hz[sim_calb_tmr])) {       /* Calibrated Timer
         if (inst_delay_d > (double)inst_til_calib) {        /* long wait? */
             stat = sim_clock_coschedule_tmr (uptr, sim_calb_tmr, ticks_til_calib - 1);
             uptr->usecs_remaining = (stat == SCPE_OK) ? usec_delay - usecs_til_calib : 0.0;
-            sim_debug (DBG_TIM, &sim_timer_dev, "sim_timer_activate_after(%s, %.0f usecs) - coscheduling with with calibrated timer(%d), ticks=%d, usecs_remaining=%.0f usecs, inst_til_tick=%d\n", 
-                       sim_uname(uptr), usec_delay, sim_calb_tmr, ticks_til_calib, uptr->usecs_remaining, inst_til_tick);
+            sim_debug (DBG_TIM, &sim_timer_dev, "sim_timer_activate_after(%s, %.0f usecs) - coscheduling with with calibrated timer(%d), ticks=%d, usecs_remaining=%.0f usecs, inst_til_tick=%d, ticks_til_calib=%d\n", 
+                       sim_uname(uptr), usec_delay, sim_calb_tmr, ticks_til_calib, uptr->usecs_remaining, inst_til_tick, ticks_til_calib);
             sim_debug (DBG_CHK, &sim_timer_dev, "sim_timer_activate_after(%s, %.0f usecs) - result = %.0f usecs, %.0f usecs\n", 
                        sim_uname(uptr), usec_delay, sim_timer_activate_time_usecs (ouptr), sim_timer_activate_time_usecs (uptr));
             return stat;
@@ -3018,7 +3019,7 @@ if (uptr->cancel == &_sim_coschedule_cancel) {
                 accum += cptr->time;
             if (cptr == uptr) {
                 result = uptr->usecs_remaining + ceil(1000000.0 * ((rtc_currd[tmr] * accum) + sim_activate_time (&sim_timer_units[tmr]) - 1) / sim_timer_inst_per_sec ());
-                sim_debug (DBG_QUE, &sim_timer_dev, "sim_timer_activate_time_usecs(%s) coscheduled - %.0f usecs, inst_per_sec=%.0f, tmr=%d, ticksize=%d, ticks=%d, inst_til_tick=%d\n", sim_uname (uptr), result, sim_timer_inst_per_sec (), tmr, rtc_currd[tmr], accum, sim_activate_time (&sim_timer_units[tmr]) - 1);
+                sim_debug (DBG_QUE, &sim_timer_dev, "sim_timer_activate_time_usecs(%s) coscheduled - %.0f usecs, inst_per_sec=%.0f, tmr=%d, ticksize=%d, ticks=%d, inst_til_tick=%d, usecs_remaining=%.0f\n", sim_uname (uptr), result, sim_timer_inst_per_sec (), tmr, rtc_currd[tmr], accum, sim_activate_time (&sim_timer_units[tmr]) - 1, uptr->usecs_remaining);
                 return result;
                 }
             }
@@ -3027,17 +3028,17 @@ if (uptr->cancel == &_sim_coschedule_cancel) {
 for (tmr=0; tmr<=SIM_NTIMERS; tmr++) {
     if ((uptr == sim_clock_unit[tmr]) && (uptr->next)) {
         result = sim_clock_unit[tmr]->usecs_remaining + (1000000.0 * (sim_activate_time (&sim_timer_units[tmr]) - 1)) / sim_timer_inst_per_sec ();
-        sim_debug (DBG_QUE, &sim_timer_dev, "sim_timer_activate_time_usecs(%s) clock - %.0f usecs, inst_per_sec=%.0f\n", sim_uname (uptr), result, sim_timer_inst_per_sec ());
+        sim_debug (DBG_QUE, &sim_timer_dev, "sim_timer_activate_time_usecs(%s) clock - %.0f usecs, inst_per_sec=%.0f, usecs_remaining=%.0f\n", sim_uname (uptr), result, sim_timer_inst_per_sec (), uptr->usecs_remaining);
         return result;
         }
     if ((uptr == &sim_timer_units[tmr]) && (uptr->next)){
         result = uptr->usecs_remaining + (1000000.0 * (sim_activate_time (uptr) - 1)) / sim_timer_inst_per_sec ();
-        sim_debug (DBG_QUE, &sim_timer_dev, "sim_timer_activate_time_usecs(%s) clock - %.0f usecs, inst_per_sec=%.0f\n", sim_uname (uptr), result, sim_timer_inst_per_sec ());
+        sim_debug (DBG_QUE, &sim_timer_dev, "sim_timer_activate_time_usecs(%s) clock - %.0f usecs, inst_per_sec=%.0f, usecs_remaining=%.0f\n", sim_uname (uptr), result, sim_timer_inst_per_sec (), uptr->usecs_remaining);
         return result;
         }
     }
 result = uptr->usecs_remaining + (1000000.0 * (sim_activate_time (uptr) - 1)) / sim_timer_inst_per_sec ();
-sim_debug (DBG_QUE, &sim_timer_dev, "sim_timer_activate_time_usecs(%s) clock - %.0f usecs, inst_per_sec=%.0f\n", sim_uname (uptr), result, sim_timer_inst_per_sec ());
+sim_debug (DBG_QUE, &sim_timer_dev, "sim_timer_activate_time_usecs(%s) clock - %.0f usecs, inst_per_sec=%.0f, usecs_remaining=%.0f\n", sim_uname (uptr), result, sim_timer_inst_per_sec (), uptr->usecs_remaining);
 return result;                                          /* Not found. */    
 }
 
diff --git a/sim_tmxr.c b/sim_tmxr.c
index 3f4cc81d..98461014 100644
--- a/sim_tmxr.c
+++ b/sim_tmxr.c
@@ -4136,18 +4136,18 @@ if (!(uptr->dynflags & UNIT_TM_POLL))
     return _sim_activate (uptr, interval);              /* Handle the non mux case */
 sooner = _tmxr_activate_delay (uptr, interval);
 if (sooner != interval) {
-    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "scheduling %s after %d instructions rather than %d instructions\n", sim_uname (uptr), sooner, interval);
+    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_activate() - scheduling %s after %d instructions rather than %d instructions\n", sim_uname (uptr), sooner, interval);
     return _sim_activate (uptr, sooner);                /* Handle the busy case */
     }
 #if defined(SIM_ASYNCH_MUX)
 if (!sim_asynch_enabled) {
-    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "scheduling %s after %d instructions\n", sim_uname (uptr), interval);
+    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_activate() - scheduling %s after %d instructions\n", sim_uname (uptr), interval);
     return _sim_activate (uptr, interval);
     }
-sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "scheduling %s asynchronously instead of %d instructions\n", sim_uname (uptr), interval);
+sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_activate() - scheduling %s asynchronously instead of %d instructions\n", sim_uname (uptr), interval);
 return SCPE_OK;
 #else
-sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "scheduling %s after %d instructions\n", sim_uname (uptr), interval);
+sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_activate() - scheduling %s after %d instructions\n", sim_uname (uptr), interval);
 return _sim_activate (uptr, interval);
 #endif
 }
@@ -4170,21 +4170,21 @@ if (!(uptr->dynflags & UNIT_TM_POLL))
 sooner = _tmxr_activate_delay (uptr, 0x7FFFFFFF);
 if (sooner != 0x7FFFFFFF) {
     if (sooner < 0) {
-        sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "scheduling %s for %u usecs produced overflow interval %d instructions, sceduling for %d instructions\n", sim_uname (uptr), usecs_walltime, sooner, 0x7FFFFFFF);
+        sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_activate_after() - scheduling %s for %u usecs produced overflow interval %d instructions, sceduling for %d instructions\n", sim_uname (uptr), usecs_walltime, sooner, 0x7FFFFFFF);
         sooner = _tmxr_activate_delay (uptr, 0x7FFFFFFF);   /* Breakpoint here on unexpected value */
         }
-    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "scheduling %s after %d instructions rather than %u usecs\n", sim_uname (uptr), sooner, usecs_walltime);
+    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_activate_after() - scheduling %s after %d instructions rather than %u usecs\n", sim_uname (uptr), sooner, usecs_walltime);
     return _sim_activate (uptr, sooner);                        /* Handle the busy case directly */
     }
 #if defined(SIM_ASYNCH_MUX)
 if (!sim_asynch_enabled) {
-    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "scheduling %s after %u usecs\n", sim_uname (uptr), usecs_walltime);
+    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_activate_after() - scheduling %s after %u usecs\n", sim_uname (uptr), usecs_walltime);
     return _sim_activate_after (uptr, (double)usecs_walltime);
     }
-sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "scheduling %s asynchronously instead of %u usecs\n", sim_uname (uptr), usecs_walltime);
+sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_activate_after() - scheduling %s asynchronously instead of %u usecs\n", sim_uname (uptr), usecs_walltime);
 return SCPE_OK;
 #else
-sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "scheduling %s after %u usecs\n", sim_uname (uptr), usecs_walltime);
+sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_activate_after() - scheduling %s after %.0f usecs\n", sim_uname (uptr), (double)usecs_walltime);
 return _sim_activate_after (uptr, (double)usecs_walltime);
 #endif
 }
@@ -4220,17 +4220,17 @@ if (!(uptr->dynflags & UNIT_TM_POLL))
     return sim_clock_coschedule_tmr (uptr, tmr, ticks); /* Handle the non mux case */
 sooner = _tmxr_activate_delay (uptr, interval);
 if (sooner != interval) {
-    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "scheduling %s after %d instructions rather than %d ticks (%d instructions)\n", sim_uname (uptr), sooner, ticks, interval);
+    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_clock_coschedule_tmr() - scheduling %s after %d instructions rather than %d ticks (%d instructions)\n", sim_uname (uptr), sooner, ticks, interval);
     return _sim_activate (uptr, sooner);                /* Handle the busy case directly */
     }
 #if defined(SIM_ASYNCH_MUX)
 if (!sim_asynch_enabled) {
-    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "coscheduling %s after interval %d ticks\n", sim_uname (uptr), ticks);
+    sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_clock_coschedule_tmr() - coscheduling %s after interval %d ticks\n", sim_uname (uptr), ticks);
     return sim_clock_coschedule (uptr, tmr, ticks);
     }
 return SCPE_OK;
 #else
-sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "coscheduling %s after interval %d ticks\n", sim_uname (uptr), ticks);
+sim_debug (TIMER_DBG_MUX, &sim_timer_dev, "tmxr_clock_coschedule_tmr() - coscheduling %s after interval %d ticks\n", sim_uname (uptr), ticks);
 return sim_clock_coschedule_tmr (uptr, tmr, ticks);
 #endif
 }