From 284a7586ca6e6a61c42eb5e1b0f720875e3c58b9 Mon Sep 17 00:00:00 2001
From: Richard Cornwell <rcornwell@github.com>
Date: Mon, 22 Jul 2019 23:05:59 -0400
Subject: [PATCH] KA10: Fixed Quantum timer to match hardware.

---
 PDP10/kx10_cpu.c  | 25 ++++++++++++++-----------
 PDP10/kx10_defs.h |  1 +
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/PDP10/kx10_cpu.c b/PDP10/kx10_cpu.c
index 60b10fc..e9ae080 100644
--- a/PDP10/kx10_cpu.c
+++ b/PDP10/kx10_cpu.c
@@ -813,12 +813,12 @@ int opflags[] = {
 void
 set_quantum()
 {
+    double us;
     sim_cancel(&cpu_unit[1]);
-    if ((qua_time & RSIGN) == 0) {
-        double us;
-        us = (double)(RSIGN - qua_time);
-        (void)sim_activate_after_d(&cpu_unit[1], us);
-    }
+    if (qua_time & BIT17)
+       return;
+    us = (double)(BIT17 - qua_time);
+    (void)sim_activate_after_d(&cpu_unit[1], us);
 }
 
 /*
@@ -830,7 +830,10 @@ load_quantum()
     if (sim_is_active(&cpu_unit[1])) {
        double us;
        us = sim_activate_time_usecs (&cpu_unit[1]);
-       qua_time = RSIGN - (uint32)us;
+       if ((uint32)us > BIT17)
+          qua_time = BIT17;
+       else
+          qua_time = (BIT17 - (uint32)us) & RMASK;
        sim_cancel(&cpu_unit[1]);
     }
 }
@@ -841,11 +844,11 @@ load_quantum()
 uint32
 get_quantum()
 {
-    uint32  t = 0;
+    uint32  t = qua_time;
     if (sim_is_active(&cpu_unit[1])) {
        double us;
        us = sim_activate_time_usecs (&cpu_unit[1]);
-       t = RSIGN - (uint32)us;
+       t = (BIT17 - (uint32)us) & RMASK;
     }
     return t;
 }
@@ -3491,9 +3494,10 @@ dpnorm:
                       AB = (AB + 1) & RMASK;
                       MB = M[AB];                /* WD 3 */
                       /* Store Quantum */
-                      qua_time = MB & RMASK;
+                      qua_time = MB & (RMASK|BIT17);
                       set_quantum();
                       fault_data = (MB >> 18) & RMASK;
+                      fault_data &= ~1; /* Clear high quantum bit */
                       mem_prot = 0;
                       if ((fault_data & 0777772) != 0)
                           mem_prot = 1;
@@ -5997,9 +6001,8 @@ qua_srv(UNIT * uptr)
 {
     if ((fault_data & 1) == 0 && pi_enable && !pi_pending && (FLAGS & USER) != 0) {
        mem_prot = 1;
-       fault_data |= 1;
     }
-    qua_time = RSIGN;
+    qua_time = BIT17;
     return SCPE_OK;
 }
 #endif
diff --git a/PDP10/kx10_defs.h b/PDP10/kx10_defs.h
index 26f2b5e..d4bb9ce 100644
--- a/PDP10/kx10_defs.h
+++ b/PDP10/kx10_defs.h
@@ -167,6 +167,7 @@ extern DEBTAB crd_debug[];
 #define BIT9     00000400000000LL
 #define BIT10    00000200000000LL
 #define BIT10_35 00000377777777LL
+#define BIT17    00000001000000LL
 #define MANT     00000777777777LL
 #define EXPO     00377000000000LL
 #define FPHBIT   01000000000000000000000LL