rtio: raise RTIOSequenceError exceptions when events are not submitted in-order

artiq/devices/rtio_core.py

@@ -1,4 +1,5 @@
 from artiq.language.core import *
+from artiq.devices.runtime_exceptions import RTIOSequenceError
 
 
 class _RTIOBase(AutoContext):
@@ -16,6 +17,8 @@ class _RTIOBase(AutoContext):
 
     @kernel
     def _set_value(self, value):
+        if now() < self.previous_timestamp:
+            raise RTIOSequenceError
         if self.previous_value != value:
             if self.previous_timestamp == now():
                 syscall("rtio_replace", now(), self.channel, value)

artiq/devices/runtime_exceptions.py

@@ -6,13 +6,28 @@ from artiq.language.core import RuntimeException
 # Must be kept in sync with soc/runtime/exceptions.h
 
 class OutOfMemory(RuntimeException):
+    """Raised when the runtime fails to allocate memory.
+
+    """
     eid = 0
 
 
 class RTIOUnderflow(RuntimeException):
+    """Raised when the CPU fails to submit a RTIO event early enough (with respect to the event's timestamp).
+
+    """
     eid = 1
 
 
+# Raised by RTIO driver for regular RTIO.
+# Raised by runtime for DDS FUD.
+class RTIOSequenceError(RuntimeException):
+    """Raised when an event was not submitted with an increasing timestamp.
+
+    """
+    eid = 2
+
+
 exception_map = {e.eid: e for e in globals().values()
                  if inspect.isclass(e)
                  and issubclass(e, RuntimeException)

doc/manual/drivers_reference.rst

@@ -12,3 +12,9 @@ Drivers reference
 
 .. automodule:: artiq.devices.dds_core
     :members:
+
+:mod:`artiq.devices.runtime_exceptions` module
+----------------------------------------------
+
+.. automodule:: artiq.devices.runtime_exceptions
+    :members:

soc/runtime/dds.c

@@ -28,8 +28,11 @@ static void fud_sync(void)
 static void fud(long long int fud_time)
 {
     int r;
+    static int previous_fud_time;
 
     r = rtio_reset_read();
+    if(r)
+        previous_fud_time = 0;
     rtio_reset_write(0);
 
     rtio_chan_sel_write(RTIO_FUD_CHANNEL);
@@ -37,6 +40,9 @@ static void fud(long long int fud_time)
         rtio_counter_update_write(1);
         fud_time = rtio_counter_read() + 3000;
     }
+    if(fud_time < previous_fud_time)
+        exception_raise(EID_RTIO_SEQUENCE_ERROR);
+
     rtio_o_timestamp_write(fud_time);
     rtio_o_value_write(1);
     rtio_o_we_write(1);

soc/runtime/exceptions.h

@@ -3,7 +3,8 @@
 
 enum {
 	EID_OUT_OF_MEMORY = 0,
-	EID_RTIO_UNDERFLOW = 1
+	EID_RTIO_UNDERFLOW = 1,
+	EID_RTIO_SEQUENCE_ERROR = 2
 };
 
 int exception_setjmp(void *jb) __attribute__((returns_twice));

test/full_stack.py

@@ -163,6 +163,17 @@ class _RTIOUnderflow(AutoContext):
             self.o.pulse(25*ns)
 
 
+class _RTIOSequenceError(AutoContext):
+    parameters = "o"
+
+    @kernel
+    def run(self):
+        t = now()
+        self.o.pulse(25*us)
+        at(t)
+        self.o.pulse(25*us)
+
+
 class RTIOCase(unittest.TestCase):
     def test_loopback(self):
         npulses = 4
@@ -186,3 +197,13 @@ class RTIOCase(unittest.TestCase):
             )
             with self.assertRaises(runtime_exceptions.RTIOUnderflow):
                 uut.run()
+
+    def test_sequence_error(self):
+        with corecom_serial.CoreCom() as com:
+            coredev = core.Core(com)
+            uut = _RTIOSequenceError(
+                core=coredev,
+                o=rtio_core.RTIOOut(core=coredev, channel=1)
+            )
+            with self.assertRaises(runtime_exceptions.RTIOSequenceError):
+                uut.run()