driver: power: siglent: make the measured power reading optional

labgrid/driver/power/siglent.py

@@ -38,13 +38,18 @@ def power_show(host, port, index):
     with _get_psu(host) as psu:
         v_measured = psu.query(f"MEAS:VOLT? CH{index}")
         a_measured = psu.query(f"MEAS:CURR? CH{index}")
-        w_measured = psu.query(f"MEAS:POWE? CH{index}")
+        # Not every SPD model implements MEAS:POWE?; such a model leaves the
+        # query unanswered, so the read times out and raises VisaIOError.
+        try:
+            w_measured = float(psu.query(f"MEAS:POWE? CH{index}"))
+        except (ValueError, pyvisa.VisaIOError):
+            w_measured = None
         v_set = psu.query(f"CH{index}:VOLT?")
         a_set = psu.query(f"CH{index}:CURR?")
     return {
         "voltage": float(v_measured),
         "amps": float(a_measured),
-        "watts": float(w_measured),
+        "watts": w_measured,
         "v_limit": float(v_set),
         "a_limit": float(a_set)
     }

labgrid/driver/powerdriver.py

@@ -7,7 +7,7 @@
 
 from ..exceptions import InvalidConfigError
 from ..factory import target_factory
-from ..protocol import PowerProtocol, DigitalOutputProtocol, ResetProtocol, ProgrammablePowerProtocol
+from ..protocol import PowerProtocol, DigitalOutputProtocol, ResetProtocol
 from ..resource import NetworkPowerPort
 from ..step import step
 from ..util.proxy import proxymanager

labgrid/remote/client.py

@@ -988,12 +988,11 @@ def power(self):
         if action == "get":
             print(f"power{' ' + name if name else ''} for place {place.name} is {'on' if res else 'off'}")
         elif action == "show":
-            print(
-                f"Voltage: {res['voltage']}V [{res['v_limit']}V], "
-                f"Current: {res['amps']}A [{res['a_limit']}A], "
-                f"Power: {res['watts']}W"
-            )
-
+            line = f"Voltage: {res['voltage']}V [{res['v_limit']}V], Current: {res['amps']}A [{res['a_limit']}A]"
+            # not every programmable PSU can measure power directly
+            if res.get("watts") is not None:
+                line += f", Power: {res['watts']}W"
+            print(line)
 
     def digital_io(self):
         place = self.get_acquired_place()
@@ -2006,12 +2005,8 @@ def get_parser(auto_doc_mode=False) -> "argparse.ArgumentParser | AutoProgramArg
     subparser.add_argument(
         "-t", "--delay", type=float, default=None, help="wait time in seconds between off and on during cycle"
     )
-    subparser.add_argument(
-        "-v", "--voltage", type=float, default=None, help="voltage value to be configured"
-    )
-    subparser.add_argument(
-        "-a", "--amps", type=float, default=None, help="amps value to be configured"
-    )
+    subparser.add_argument("-v", "--voltage", type=float, default=None, help="voltage value to be configured")
+    subparser.add_argument("-a", "--amps", type=float, default=None, help="amps value to be configured")
     subparser.add_argument("--name", "-n", help="optional resource name")
     subparser.set_defaults(func=ClientSession.power)
 

tests/test_powerdriver.py

@@ -368,6 +368,40 @@ def test_siglent_show(self, target, mocker):
             "a_limit": 1.5,
         }
 
+    @pytest.mark.parametrize("failure", ["unanswered", "non-numeric"])
+    def test_siglent_show_without_power_query(self, target, mocker, failure):
+        pytest.importorskip("pyvisa")
+        from pyvisa import constants, errors
+
+        # Not every SPD model implements MEAS:POWE?. Such a model leaves the
+        # query unanswered, so the read times out; report no power rather than
+        # losing the other four readings with it.
+        responses = {
+            "MEAS:VOLT? CH1": "5.001",
+            "MEAS:CURR? CH1": "0.209",
+            "CH1:VOLT?": "5.0",
+            "CH1:CURR?": "1.5",
+        }
+
+        def query(cmd):
+            if cmd in responses:
+                return responses[cmd]
+            if failure == "unanswered":
+                raise errors.VisaIOError(constants.StatusCode.error_timeout)
+            return "not a number"
+
+        psu = self._mock_siglent_psu(mocker)
+        psu.query.side_effect = query
+        d = self._activate_siglent_driver(target)
+
+        assert d.show() == {
+            "voltage": 5.001,
+            "amps": 0.209,
+            "watts": None,
+            "v_limit": 5.0,
+            "a_limit": 1.5,
+        }
+
     def test_siglent_voltage_amps(self, target, mocker):
         pytest.importorskip("pyvisa")