dds.c: turn off batch mode before an underflow can be raised.

Fixes #334.

artiq/runtime/dds.c

@@ -192,6 +192,7 @@ void dds_batch_exit(void)
 
     if(!batch_mode)
         artiq_raise_from_c("DDSBatchError", "DDS batch error", 0, 0, 0);
+    batch_mode = 0;
     /* + FUD time */
     now = batch_ref_time - batch_count*(DURATION_PROGRAM + DURATION_WRITE);
     for(i=0;i<batch_count;i++) {
@@ -201,7 +202,6 @@ void dds_batch_exit(void)
             batch[i].amplitude);
         now += DURATION_PROGRAM + DURATION_WRITE;
     }
-    batch_mode = 0;
 }
 
 void dds_set(long long int timestamp, int bus_channel, int channel,

artiq/test/coredevice/test_rtio.py

@@ -102,6 +102,32 @@ class PulseRate(EnvExperiment):
                 break
 
 
+class PulseRateDDS(EnvExperiment):
+    def build(self):
+        self.setattr_device("core")
+        self.setattr_device("core_dds")
+        self.setattr_device("dds0")
+        self.setattr_device("dds1")
+
+    @kernel
+    def run(self):
+        dt = seconds_to_mu(150*us)
+        while True:
+            try:
+                delay(10*ms)
+                for i in range(100):
+                    with self.core_dds.batch:
+                        self.dds0.set(100*MHz)
+                        self.dds1.set(100*MHz)
+                    delay_mu(dt)
+            except RTIOUnderflow:
+                dt += 100
+                self.core.break_realtime()
+            else:
+                self.set_dataset("pulse_rate", mu_to_seconds(2*dt))
+                break
+
+
 class Watchdog(EnvExperiment):
     def build(self):
         self.setattr_device("core")
@@ -228,6 +254,13 @@ class CoredeviceTest(ExperimentCase):
         self.assertGreater(rate, 100*ns)
         self.assertLess(rate, 2500*ns)
 
+    def test_pulse_rate_dds(self):
+        self.execute(PulseRateDDS)
+        rate = self.dataset_mgr.get("pulse_rate")
+        print(rate)
+        self.assertGreater(rate, 100*us)
+        self.assertLess(rate, 2500*us)
+
     def test_loopback_count(self):
         npulses = 2
         self.execute(LoopbackCount, npulses=npulses)