Finish implementing the timer update interrupt

Most of the logic was already there, but the update interrupt flag
needed to be connected to the NVIC.

Note that the trigger interrupt flag is still not connected to the NVIC,
so trigger interrupts will not work.

Author: beckus

hw/timer/stm32_timer.c

@@ -194,12 +194,19 @@ static void stm32_timer_update(Stm32Timer *s)
 	}
 }
 
+static void stm32_timer_update_UIF(Stm32Timer *s, uint8_t value) {
+    s->sr &= ~0x1; /* update interrupt flag in status reg */
+    s->sr |= 0x1;
+
+    qemu_set_irq(s->irq, value);
+}
+
 static void stm32_timer_tick(void *opaque)
 {
     Stm32Timer *s = (Stm32Timer *)opaque;
     DPRINTF("%s Alarm raised\n", stm32_periph_name(s->periph));
     s->itr = 1;
-	s->sr |= 0x1; /* update interrupt flag in status reg */
+    stm32_timer_update_UIF(s, 1);
 
 	if (s->countMode == TIMER_UP_COUNT)
 	{
@@ -332,6 +339,7 @@ static void stm32_timer_write(void * opaque, hwaddr offset,
 	case TIMER_SR_OFFSET:
 		s->sr ^= (value ^ 0xFFFF);
 		s->sr &= 0x1eFF;
+		stm32_timer_update_UIF(s, s->sr & 0x1);
         DPRINTF("%s sr = %x\n", stm32_periph_name(s->periph), s->sr);
 		break;
 	case TIMER_EGR_OFFSET: