coredevice: Add Core.wait_until_mu()

(This supersedes TTLOut.sync(), see see GitHub #1113.)

artiq/coredevice/core.py

@@ -153,6 +153,17 @@ class Core:
     def get_rtio_counter_mu(self):
         return rtio_get_counter()
 
+    @kernel
+    def wait_until_mu(self, cursor_mu):
+        """Block execution until the hardware RTIO counter reaches the given
+        value (see :meth:`get_rtio_counter_mu`).
+
+        If the hardware counter has already passed the given time, the function
+        returns immediately.
+        """
+        while self.get_rtio_counter_mu() < cursor_mu:
+            pass
+
     @kernel
     def get_drtio_link_status(self, linkno):
         """Returns whether the specified DRTIO link is up.

artiq/test/coredevice/test_rtio.py

@@ -29,6 +29,23 @@ class RTIOCounter(EnvExperiment):
         self.set_dataset("dt", self.core.mu_to_seconds(t1 - t0))
 
 
+class InvalidCounter(Exception):
+    pass
+
+
+class WaitForRTIOCounter(EnvExperiment):
+    def build(self):
+        self.setattr_device("core")
+
+    @kernel
+    def run(self):
+        self.core.break_realtime()
+        target_mu = now_mu() + 10000
+        self.core.wait_until_mu(target_mu)
+        if self.core.get_rtio_counter_mu() < target_mu:
+            raise InvalidCounter
+
+
 class PulseNotReceived(Exception):
     pass
 
@@ -375,6 +392,9 @@ class CoredeviceTest(ExperimentCase):
         self.assertGreater(dt, 50*ns)
         self.assertLess(dt, 1*us)
 
+    def test_wait_for_rtio_counter(self):
+        self.execute(WaitForRTIOCounter)
+
     def test_loopback(self):
         self.execute(Loopback)
         rtt = self.dataset_mgr.get("rtt")