reorder check to ensure that flag is allowed to be raised within ISR,…

… but no nested IRQs occur

simavr/sim/sim_interrupts.c

@@ -115,23 +115,25 @@ avr_raise_interrupt(
 	if (!vector || !vector->vector)
 		return 0;
 
-	if (vector->pending) {
-		if (vector->trace)
-			printf("IRQ%d:I=%d already raised (enabled %d) (cycle %lld pc 0x%x)\n",
-				vector->vector, !!avr->sreg[S_I], avr_regbit_get(avr, vector->enable),
-				(long long int)avr->cycle, avr->pc);
-        // no return - polling ISR within interrupt allowed
-	}
-
 	if (vector->trace)
 		printf("IRQ%d raising (enabled %d)\n",
 			vector->vector, avr_regbit_get(avr, vector->enable));
+
 	// always mark the 'raised' flag to one, even if the interrupt is disabled
 	// this allow "polling" for the "raised" flag, like for non-interrupt
 	// driven UART and so so. These flags are often "write one to clear"
 	if (vector->raised.reg)
 		avr_regbit_set(avr, vector->raised);
 
+	if (vector->pending) {
+		if (vector->trace)
+			printf("IRQ%d:I=%d already raised (enabled %d) (cycle %lld pc 0x%x)\n",
+				vector->vector, !!avr->sreg[S_I], avr_regbit_get(avr, vector->enable),
+				(long long int)avr->cycle, avr->pc);
+
+        return 0;
+	}
+
 	avr_raise_irq(vector->irq + AVR_INT_IRQ_PENDING, 1);
 	avr_raise_irq(avr->interrupts.irq + AVR_INT_IRQ_PENDING, 1);