Alarms¶

An alarm definition tells Yamcs when a parameter value is a reason for concern, and how concerned to be. Yamcs evaluates alarms as values arrive and surfaces them to operators for acknowledgment.

Alarm severity uses six levels, in increasing order of concern:

`NORMAL`	No concern.
`WATCH`	Least concern, below the commonly used WARNING.
`WARNING`	The usual minimum concern level.
`DISTRESS`	Between WARNING and CRITICAL.
`CRITICAL`	The usual maximum concern level.
`SEVERE`	Highest concern, above CRITICAL.

These are the values of the AlarmLevel enum. Most missions use only WARNING and CRITICAL.

Threshold alarms¶

For numeric parameters (IntegerParameter, FloatParameter), ThresholdAlarm defines low and/or high limits per severity level. Each limit is optional; each has an *_exclusive companion to exclude the boundary value itself.

battery_voltage = Y.FloatParameter(
    system=eps,
    name="battery_voltage",
    units="V",
    encoding=Y.uint12_t,
    calibrator=Y.Polynomial([0, 0.00805]),
    alarm=Y.ThresholdAlarm(
        watch_low=11.5,
        warning_low=11.0,
        critical_low=10.2,
        warning_high=14.4,
        critical_high=15.0,
    ),
)

Available limits: watch_low, warning_low, distress_low, critical_low, severe_low and the corresponding *_high options. Thresholds compare against the calibrated engineering value.

minimum_violations (default 1) requires the limit to be violated that many successive times before the alarm triggers, filtering out one-sample glitches.

Enumeration alarms¶

For EnumeratedParameter, EnumerationAlarm assigns an alarm level per state, keyed by enumeration label. States not listed get the default_level (NORMAL unless overridden):

mode = Y.EnumeratedParameter(
    system=obc,
    name="mode",
    choices=[(0, "OFF"), (1, "SAFE"), (2, "NOMINAL")],
    encoding=Y.uint8_t,
    alarm=Y.EnumerationAlarm(
        states={"SAFE": Y.AlarmLevel.WARNING},
    ),
)

Setting default_level to a non-normal value inverts the logic: every state alarms unless explicitly declared safe.

Context alarms¶

Alarm limits often depend on the situation: a battery current that is nominal during transmission would be alarming in idle mode. Context alarms attach an alternative alarm specification that applies while a condition — an expression over other parameters — holds:

current = Y.FloatParameter(
    system=eps,
    name="bus_current",
    units="A",
    encoding=Y.uint12_t,
    alarm=Y.ThresholdAlarm(warning_high=1.0),
    context_alarms=[
        Y.ThresholdContextAlarm(
            context=Y.eq(mode, "TRANSMIT"),
            alarm=Y.ThresholdAlarm(warning_high=3.5),
        ),
    ],
)

While the context matches, the context alarm’s specification replaces the default one. EnumerationContextAlarm is the equivalent for enumerated parameters. Multiple context alarms may be given; the plain alarm serves as the fallback when no context matches.