pxi6733: refactor, allow multiple channels in one task, cancel any previous task

artiq/devices/pxi6733/driver.py

@@ -14,22 +14,38 @@ class DAQmxSim:
     def ping(self):
         return True
 
+def string_to_bytes(string, name):
+    if isinstance(string, str):
+        string = bytes(string, encoding="ascii")
+    elif not isinstance(string, bytes):
+        raise ValueError("{} must be of either str or bytes type".format(name))
+    return string
 
 class DAQmx:
     """NI PXI6733 DAQ interface."""
 
-    def __init__(self, device, analog_output, clock):
+    def __init__(self, channels, clock):
+        """
+        :param channels: List of channels as a string or bytes(), following
+            the physical channels lists and ranges NI-DAQmx syntax.
+
+            Example: Dev1/ao0, Dev1/ao1:ao3
+        :param clock: Clock source terminal as a string or bytes(), following
+            NI-DAQmx terminal names syntax.
+
+            Example: PFI5
+        """
+
         import PyDAQmx as daq
 
-        self.device = device
-        self.analog_output = analog_output
-        self.clock = clock
-        self.tasks = []
+        self.channels = string_to_bytes(channels, "channels")
+        self.clock = string_to_bytes(clock, "clock")
+        self.task = None
         self.daq = daq
 
     def done_callback_py(self, taskhandle, status, callback_data):
-        self.daq.DAQmxClearTask(taskhandle)
-        self.tasks.remove(taskhandle)
+        if taskhandle == self.task:
+            self.clear_pending_task()
 
     def ping(self):
         try:
@@ -42,43 +58,75 @@ class DAQmx:
     def load_sample_values(self, sampling_freq, values):
         """Load sample values into PXI 6733 device.
 
-        This loads sample values into the PXI 6733 device and then
-        configures a task to output those samples at each clock rising
-        edge.
+        This loads sample values into the PXI 6733 device.
+        The device will output samples at each clock rising edge.
+        The first sample is output at the first clock rising edge.
 
-        A callback is registered to clear the task (deallocate resources)
-        when the task has completed.
+        When using several channels simultaneously, you must concatenate the
+        values for the different channels in the ``values`` array.
+        The sample values for the same channel must be grouped together.
+
+        Example:
+
+        >>> values = np.array([ch0_samp0, ch0_samp1, ch1_samp0, ch1_samp1],
+                              dtype=float)
+
+        In this example the first two samples will be output via the first
+        channel and the two following samples will be output via the second
+        channel.
+
+        Any call to this method will cancel any previous task even if it has
+        not yet completed.
 
         :param sampling_freq: The sampling frequency in samples per second.
         :param values: A numpy array of sample values to load in the device.
         """
 
+        self.clear_pending_task()
+
         t = self.daq.Task()
-        t.CreateAOVoltageChan(self.device+b"/"+self.analog_output, b"",
+        t.CreateAOVoltageChan(self.channels, b"",
                               min(values), max(values),
                               self.daq.DAQmx_Val_Volts, None)
+
+        channel_number = self.daq.int32()
+        t.GetTaskNumChans(byref(channel_number))
+        nb_values = len(values)
+        if nb_values % channel_number.value > 0:
+            self.daq.DAQmxClearTask(t.taskHandle)
+            raise ValueError("The size of the values array must be a multiple "
+                             "of the number of channels ({})"
+                             .format(channel_number.value))
+        samps_per_channel = nb_values // channel_number
+
         t.CfgSampClkTiming(self.clock, sampling_freq,
                            self.daq.DAQmx_Val_Rising,
-                           self.daq.DAQmx_Val_FiniteSamps, len(values))
+                           self.daq.DAQmx_Val_FiniteSamps, samps_per_channel)
         num_samps_written = self.daq.int32()
         values = np.require(values, dtype=float,
                             requirements=["C_CONTIGUOUS", "WRITEABLE"])
-        ret = t.WriteAnalogF64(len(values), False, 0,
+        ret = t.WriteAnalogF64(samps_per_channel, False, 0,
                                self.daq.DAQmx_Val_GroupByChannel, values,
                                byref(num_samps_written), None)
-        if num_samps_written.value != len(values):
+        if num_samps_written.value != nb_values:
             raise IOError("Error: only {} sample values were written"
                           .format(num_samps_written.value))
         if ret:
             raise IOError("Error while writing samples to the channel buffer")
 
         done_cb = self.daq.DAQmxDoneEventCallbackPtr(self.done_callback_py)
-        self.tasks.append(t.taskHandle)
+        self.task = t.taskHandle
         self.daq.DAQmxRegisterDoneEvent(t.taskHandle, 0, done_cb, None)
         t.StartTask()
 
-    def close(self):
-        """Clear all pending tasks."""
+    def clear_pending_task(self):
+        """Clear any pending task."""
 
-        for t in self.tasks:
-            self.daq.DAQmxClearTask(t)
+        if self.task is not None:
+            self.daq.DAQmxClearTask(self.task)
+            self.task = None
+
+    def close(self):
+        """Free any allocated resources."""
+
+        self.clear_pending_task()

artiq/frontend/pxi6733_controller.py

@@ -11,13 +11,11 @@ from artiq.tools import verbosity_args, init_logger, simple_network_args
 def get_argparser():
     parser = argparse.ArgumentParser(description="NI PXI 6733 controller")
     simple_network_args(parser, 3256)
-    parser.add_argument("-d", "--device", default=None,
-                        help="Device name (e.g. Dev1)."
+    parser.add_argument("-C", "--channels", default=None,
+                        help="List of channels (e.g. Dev1/ao0, Dev1/ao1:3)."
                         " Omit for simulation mode.")
     parser.add_argument("-c", "--clock", default="PFI5",
                         help="Input clock pin name (default: PFI5)")
-    parser.add_argument("-a", "--analog-output", default="ao0",
-                        help="Analog output pin name (default: ao0)")
     verbosity_args(parser)
     return parser
 
@@ -26,12 +24,11 @@ def main():
     args = get_argparser().parse_args()
     init_logger(args)
 
-    if args.device is None:
+    if args.channels is None:
         daq = DAQmxSim()
     else:
-        daq = DAQmx(bytes(args.device, "ascii"),
-                    bytes(args.analog_output, "ascii"),
-                    bytes(args.clock, "ascii"))
+        daq = DAQmx(args.channels,
+                    args.clock)
 
     try:
         simple_server_loop({"pxi6733": daq},