Fixed a hardware interrupt signalling check in MAINDEC Test #15

modules/pdp11/lib/cpustate.js

@@ -745,7 +745,7 @@ CPUStatePDP11.prototype.removeTrigger = function(trigger)
             triggerPrev = triggerNext;
         }
     }
-    // We could also set trigger.next to null now, but strictly speaking, that shouldn't be necessary
+    // We could also set trigger.next to null now, but strictly speaking, that shouldn't be necessary.
 };
 
 /**
@@ -757,16 +757,12 @@ CPUStatePDP11.prototype.removeTrigger = function(trigger)
  */
 CPUStatePDP11.prototype.setTrigger = function(trigger)
 {
-    /*
-     * We COULD dispatch interrupts immediately, but there are compatibility reasons for ONLY doing so
-     * inside the stepCPU() loop; see that function for details.
-     *
-     *      if (this.dispatchInterrupt(trigger.vector, trigger.priority)) {
-     *          return true;
-     *      }
-     */
     this.insertTrigger(trigger);
-    this.opFlags |= PDP11.OPFLAG.INTQ;
+    /*
+     * See the writeXCSR() function for an explanation of why signalling an INTQ hardware interrupt condition
+     * should be done using INTQ_DELAY rather than setting INTQ directly.
+     */
+    this.opFlags |= PDP11.OPFLAG.INTQ_DELAY;
     return false;
 };
 

modules/pdp11/lib/serialport.js

@@ -663,7 +663,19 @@ SerialPortPDP11.prototype.writeXCSR = function(data, addr)
 {
     /*
      * If the device is READY, and TIE is being set, then request an interrupt.
+     *
+     * Conversely, if TIE is being cleared, remove the request; this satisfies a test in MAINDEC TEST 15,
+     * which appears to clear, set, and clear the Transmitter Interrupt Enable (TIE) bit in rapid succession,
+     * with the expectation that NO interrupt will be generated.  However, this fix also required a
+     * complementary change in setTrigger(), to signal an interrupt using INTQ_DELAY rather than INTQ.
      */
+    if (this.xcsr & PDP11.DL11.XCSR.READY) {
+        if (data & PDP11.DL11.XCSR.TIE) {
+            this.cpu.setTrigger(this.triggerTransmitInterrupt);
+        } else {
+            this.cpu.removeTrigger(this.triggerTransmitInterrupt);
+        }
+    }
     if ((this.xcsr & PDP11.DL11.XCSR.READY) && (data & PDP11.DL11.XCSR.TIE)) {
         this.cpu.setTrigger(this.triggerTransmitInterrupt);
     }