From 7ce7317f7c0722481c21a3626ad13a1884100ff7 Mon Sep 17 00:00:00 2001
From: Mark Pizzolato <mark@infocomm.com>
Date: Fri, 7 Feb 2014 11:43:52 -0800
Subject: [PATCH] PDP8: Add new breakpoint command based on instruction value
 (Opcode) (from Dave Gesswein) as discussed in issue #75

---
 PDP8/pdp8_cpu.c  | 11 +++++++++--
 PDP8/pdp8_defs.h |  7 ++++---
 PDP8/pdp8_sys.c  |  1 +
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/PDP8/pdp8_cpu.c b/PDP8/pdp8_cpu.c
index f7e42f35..67b74fe7 100644
--- a/PDP8/pdp8_cpu.c
+++ b/PDP8/pdp8_cpu.c
@@ -353,12 +353,18 @@ while (reason == 0) {                                   /* loop until halted */
         }
 
     MA = IF | PC;                                       /* form PC */
-    if (sim_brk_summ && sim_brk_test (MA, SWMASK ('E'))) { /* breakpoint? */
+    if (sim_brk_summ && 
+        sim_brk_test (MA, (1u << SIM_BKPT_V_SPC) | SWMASK ('E'))) { /* breakpoint? */
         reason = STOP_IBKPT;                            /* stop simulation */
         break;
 		}
 
     IR = M[MA];                                         /* fetch instruction */
+    if (sim_brk_summ && 
+        sim_brk_test (IR, (2u << SIM_BKPT_V_SPC) | SWMASK ('I'))) { /* breakpoint? */
+        reason = STOP_OPBKPT;                            /* stop simulation */
+        break;
+        }
     PC = (PC + 1) & 07777;                              /* increment PC */
     int_req = int_req | INT_NO_ION_PENDING;             /* clear ION delay */
     sim_interval = sim_interval - 1;
@@ -1364,7 +1370,8 @@ pcq_r = find_reg ("PCQ", NULL, dptr);
 if (pcq_r)
     pcq_r->qptr = 0;
 else return SCPE_IERR;
-sim_brk_types = sim_brk_dflt = SWMASK ('E');
+sim_brk_types = SWMASK ('E') | SWMASK('I');
+sim_brk_dflt = SWMASK ('E');
 return SCPE_OK;
 }
 
diff --git a/PDP8/pdp8_defs.h b/PDP8/pdp8_defs.h
index c52f2453..086e1ae6 100644
--- a/PDP8/pdp8_defs.h
+++ b/PDP8/pdp8_defs.h
@@ -59,9 +59,10 @@
 #define STOP_RSRV       1                               /* must be 1 */
 #define STOP_HALT       2                               /* HALT */
 #define STOP_IBKPT      3                               /* breakpoint */
-#define STOP_NOTSTD     4                               /* non-std devno */
-#define STOP_DTOFF      5                               /* DECtape off reel */
-#define STOP_LOOP       6                               /* infinite loop */
+#define STOP_OPBKPT     4                               /* Opcode/Instruction breakpoint */
+#define STOP_NOTSTD     5                               /* non-std devno */
+#define STOP_DTOFF      6                               /* DECtape off reel */
+#define STOP_LOOP       7                               /* infinite loop */
 
 /* Memory */
 
diff --git a/PDP8/pdp8_sys.c b/PDP8/pdp8_sys.c
index 1f5ddc1a..72c22732 100644
--- a/PDP8/pdp8_sys.c
+++ b/PDP8/pdp8_sys.c
@@ -119,6 +119,7 @@ const char *sim_stop_messages[] = {
     "Unimplemented instruction",
     "HALT instruction",
     "Breakpoint",
+    "Opcode Breakpoint",
     "Non-standard device number",
     "DECtape off reel",
     "Infinite loop"