From 34c4ab3cd555c37a16b6d24258c38d4ce7618681 Mon Sep 17 00:00:00 2001
From: Lars Brinkhoff <lars@nocrew.org>
Date: Wed, 26 Oct 2022 12:59:49 +0200
Subject: [PATCH] PDP11: Improve idling.

---
 PDP11/pdp11_dc.c |  2 +-
 PDP11/pdp11_dh.c |  4 ++--
 PDP11/pdp11_ng.c | 13 +++++++++----
 display/ng.c     |  6 ++++--
 4 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/PDP11/pdp11_dc.c b/PDP11/pdp11_dc.c
index 5c69839b..313f50be 100644
--- a/PDP11/pdp11_dc.c
+++ b/PDP11/pdp11_dc.c
@@ -157,7 +157,7 @@ DIB dci_dib = {
     2, IVCL (DCI), VEC_AUTO, { &dci_iack, &dco_iack }, IOLN_DC,
     };
 
-UNIT dci_unit = { UDATA (&dci_svc, 0, 0), TMLN_SPD_9600_BPS };
+UNIT dci_unit = { UDATA (&dci_svc, UNIT_IDLE, 0), TMLN_SPD_9600_BPS };
 
 REG dci_reg[] = {
     { BRDATAD (BUF,          dci_buf, DEV_RDX, 8, DCX_LINES,  "input control/stats register") },
diff --git a/PDP11/pdp11_dh.c b/PDP11/pdp11_dh.c
index 63e7bdc0..030255cc 100644
--- a/PDP11/pdp11_dh.c
+++ b/PDP11/pdp11_dh.c
@@ -81,8 +81,8 @@ DIB dh_dib = {
 };
 
 UNIT dh_unit[] = {
-  { UDATA (&dh_input_svc, UNIT_ATTABLE, 0) },
-  { UDATA (&dh_output_svc, UNIT_DIS, 0) }
+  { UDATA (&dh_input_svc, UNIT_ATTABLE | UNIT_IDLE, 0) },
+  { UDATA (&dh_output_svc, UNIT_DIS | UNIT_IDLE, 0) }
 };
 
 REG dh_reg[] = {
diff --git a/PDP11/pdp11_ng.c b/PDP11/pdp11_ng.c
index 4da8c35a..1976dfa6 100644
--- a/PDP11/pdp11_ng.c
+++ b/PDP11/pdp11_ng.c
@@ -58,7 +58,7 @@ DIB ng_dib = {
 };
 
 UNIT ng_unit = {
-  UDATA (&ng_svc, 0, 0), NG_DELAY
+  UDATA (&ng_svc, UNIT_IDLE, 0), NG_DELAY
 };
 
 REG ng_reg[] = {
@@ -133,8 +133,14 @@ t_stat
 ng_wr(int32 data, int32 PA, int32 access)
 {
   switch (PA & 002) {
-  case 000:  ng_set_csr(data); return SCPE_OK;
-  case 002:  ng_set_reloc(data); return SCPE_OK;
+  case 000:
+    ng_set_csr(data);
+    if (data & 010000)
+      sim_activate (&ng_unit, 1);
+    return SCPE_OK;
+  case 002:
+    ng_set_reloc(data);
+    return SCPE_OK;
   }
   return SCPE_NXM;
 }
@@ -185,7 +191,6 @@ ng_reset(DEVICE *dptr)
 
   CLR_INT (NG);
   ng_unit.wait = 100;
-  sim_activate (dptr->units, 1);
 
   set_cmd (0, "DZ DISABLED"); /* Conflict with NG. */
   set_cmd (0, "HK DISABLED"); /* Conflict with RF. */
diff --git a/display/ng.c b/display/ng.c
index a2715ffa..1233bb73 100644
--- a/display/ng.c
+++ b/display/ng.c
@@ -308,6 +308,7 @@ ng_cycle(int us, int slowdown)
   static uint32 usec = 0;
   static uint32 msec = 0;
   uint32 new_msec;
+  int running = 0;
   int saved;
 
   new_msec = (usec += us) / 1000;
@@ -323,7 +324,7 @@ ng_cycle(int us, int slowdown)
     if ((status[0] & 1) == 0)
       goto age_ret;
   } else if (ng_type != TYPE_DAZZLE)
-    return 1;
+    return 0;
 
   if (sync_period)
     goto age_ret;
@@ -333,6 +334,7 @@ ng_cycle(int us, int slowdown)
     if (ng_type == TYPE_DAZZLE && (status[console] & TKRUN) == 0)
       continue;
 
+    running = 1;
     time_out = fetch(dpc[console], &inst);
     DEBUGF("[%d] PC %06o, INSTR %06o\n", console, dpc[console], inst);
     dpc[console] += 2;
@@ -355,5 +357,5 @@ ng_cycle(int us, int slowdown)
 
  age_ret:
   display_age(us, slowdown);
-  return 1;
+  return running || !display_is_blank();
 }