devices/dds_core: support realtime FUD and zero-length pulse collapsing

artiq/devices/dds_core.py

@@ -1,35 +1,44 @@
 from artiq.language.core import *
 from artiq.language.units import *
+from artiq.devices import rtio_core
 
 
 class DDS(AutoContext):
     parameters = "dds_sysclk reg_channel rtio_channel"
 
     def build(self):
-        self._previous_frequency = 0*MHz
+        self.previous_frequency = 0*MHz
+        self.sw = rtio_core.RTIOOut(self, channel=self.rtio_channel)
 
-    kernel_attr = "_previous_frequency"
+    kernel_attr = "previous_frequency previous_timestamp"
-
-    @kernel
-    def _set_frequency(self, frequency):
-        if self._previous_frequency != frequency:
-            syscall("rtio_sync", self.rtio_channel)  # wait until output is off
-            syscall("dds_program", self.reg_channel,
-                    int(2**32*frequency/self.dds_sysclk))
-            self._previous_frequency = frequency
-
-    @kernel
-    def pulse(self, frequency, duration):
-        self._set_frequency(frequency)
-        syscall("rtio_set", now(), self.rtio_channel, 1)
-        delay(duration)
-        syscall("rtio_set", now(), self.rtio_channel, 0)
 
     @kernel
     def on(self, frequency):
-        self._set_frequency(frequency)
+        if self.previous_frequency != frequency:
-        syscall("rtio_set", now(), self.rtio_channel, 1)
+            if self.sw.previous_timestamp != now():
+                self.sw.sync()
+            if self.sw.previous_value:
+                # Channel is already on.
+                # Precise timing of frequency change is required.
+                fud_time = now()
+            else:
+                # Channel is off.
+                # Use soft timing on FUD to prevent conflicts when
+                # reprogramming several channels that need to be turned on at
+                # the same time.
+                fud_time = -1
+            syscall("dds_program", self.reg_channel,
+                    int(2**32*frequency/self.dds_sysclk),
+                    fud_time)
+            self.previous_frequency = frequency
+        self.sw.on()
 
     @kernel
     def off(self):
-        syscall("rtio_set", now(), self.rtio_channel, 0)
+        self.sw.off()
+
+    @kernel
+    def pulse(self, frequency, duration):
+        self.on(frequency)
+        delay(duration)
+        self.off()