Update alarm behavior documentation and enforce valueAlarm.active defaults in code

Author: MatInGit

docs/source/interfaces.rst

@@ -82,8 +82,10 @@ Alarm Behavior
 
 - Computation is scalar-only and active when ``compute_alarm: true``.
 - ``compute_alarm: true`` requires:
-  ``valueAlarm.active: true`` and limits
+  ``valueAlarm`` plus limits
   ``lowAlarmLimit``, ``lowWarningLimit``, ``highWarningLimit``, ``highAlarmLimit``.
+- ``valueAlarm.active`` defaults to ``true`` when omitted for computed alarms.
+- ``valueAlarm.active: false`` is rejected when ``compute_alarm: true``.
 - Missing severities use defaults:
   ``lowAlarmSeverity=2``, ``lowWarningSeverity=1``,
   ``highWarningSeverity=1``, ``highAlarmSeverity=2``.

poly_lithic/src/interfaces/p4p_alarm_helpers.py

@@ -54,9 +54,11 @@ def normalise_variable_settings(pv_name: str, pv_cfg: dict[str, Any]) -> dict[st
     if compute_alarm:
         if value_alarm_cfg is None:
             raise ValueError(f'{pv_name}: compute_alarm=true requires valueAlarm config')
-        if value_alarm_cfg.get('active') is not True:
+        if 'active' not in value_alarm_cfg:
+            value_alarm_cfg['active'] = True
+        elif value_alarm_cfg.get('active') is not True:
             raise ValueError(
-                f'{pv_name}: compute_alarm=true requires valueAlarm.active=true'
+                f'{pv_name}: compute_alarm=true does not allow valueAlarm.active=false'
             )
 
         missing = [field for field in ALARM_LIMIT_FIELDS if field not in value_alarm_cfg]

readme.md

@@ -276,7 +276,8 @@ Scalar PVs can compute EPICS alarm fields from ``valueAlarm`` limits:
 
 When ``compute_alarm: true``:
 
-- ``valueAlarm.active`` must be ``true``
+- ``valueAlarm.active`` defaults to ``true`` if omitted
+- ``valueAlarm.active: false`` is rejected
 - required limits: ``lowAlarmLimit``, ``lowWarningLimit``, ``highWarningLimit``, ``highAlarmLimit``
 - optional severities default to:
   ``lowAlarmSeverity=2``, ``lowWarningSeverity=1``, ``highWarningSeverity=1``, ``highAlarmSeverity=2``
@@ -301,7 +302,7 @@ flowchart TD
     D -- No --> E[No computation<br/>Write value only]
     D -- Yes --> F{compute_alarm true?}
     F -- No --> E
-    F -- Yes --> G{valueAlarm.active true<br/>and limits valid?}
+    F -- Yes --> G{valueAlarm configured<br/>active not false<br/>and limits valid?}
     G -- No --> H[Config validation error at startup]
     G -- Yes --> I[Evaluate thresholds]
     I --> J[Set alarm severity/status/message]

tests/test_p4p.py

@@ -233,7 +233,6 @@ def test_SimplePVAInterface_compute_alarm_defaults_missing_severities(monkeypatc
                 'type': 'scalar',
                 'compute_alarm': True,
                 'valueAlarm': {
-                    'active': True,
                     'lowAlarmLimit': -5.0,
                     'lowWarningLimit': -2.0,
                     'highWarningLimit': 2.0,
@@ -259,3 +258,27 @@ def fake_put(name, payload):
     assert sent[1]['alarm']['severity'] == 2
     assert sent[1]['alarm']['status'] == 3
     p4p.close()
+
+
+def test_SimplePVAInterface_reject_compute_alarm_with_active_false():
+    config = {
+        'variables': {
+            'test:float:AA': {
+                'name': 'test:float:AA',
+                'proto': 'pva',
+                'type': 'scalar',
+                'compute_alarm': True,
+                'valueAlarm': {
+                    'active': False,
+                    'lowAlarmLimit': -5.0,
+                    'lowWarningLimit': -2.0,
+                    'highWarningLimit': 2.0,
+                    'highAlarmLimit': 5.0,
+                },
+            }
+        }
+    }
+    with pytest.raises(
+        ValueError, match='compute_alarm=true does not allow valueAlarm.active=false'
+    ):
+        SimplePVAInterface(config)

tests/test_p4p_server.py

@@ -386,7 +386,6 @@ def test_scalar_compute_alarm_defaults_missing_severities():
                 'type': 'scalar',
                 'compute_alarm': True,
                 'valueAlarm': {
-                    'active': True,
                     'lowAlarmLimit': -5.0,
                     'lowWarningLimit': -2.0,
                     'highWarningLimit': 2.0,
@@ -412,3 +411,27 @@ def test_scalar_compute_alarm_defaults_missing_severities():
         assert alarm.message == 'HIHI'
     finally:
         p4p.close()
+
+
+def test_reject_server_compute_alarm_with_active_false():
+    config = {
+        'variables': {
+            'test': {
+                'name': 'test',
+                'proto': 'pva',
+                'type': 'scalar',
+                'compute_alarm': True,
+                'valueAlarm': {
+                    'active': False,
+                    'lowAlarmLimit': -5.0,
+                    'lowWarningLimit': -2.0,
+                    'highWarningLimit': 2.0,
+                    'highAlarmLimit': 5.0,
+                },
+            }
+        }
+    }
+    with pytest.raises(
+        ValueError, match='compute_alarm=true does not allow valueAlarm.active=false'
+    ):
+        SimplePVAInterfaceServer(config)