NTScalar and NTScalarArray¶
The epics:nt/NTScalar:1.0 and related epics:nt/NTScalarArray:1.0
definitions describe a primary ‘value’ and supporting meta-data.
In the case of NTScalarArray the value is a 1-d array of primitive type.
In the case of NTScalar the value is a single primitive value.
Both variants include time and alarm meta-data fields, and optionally display and control meta-data fields.
using namespace pvxs;
// single integer
Value iscalar = nt::NTScalar{TypeCode::Int64}.create();
// eg. access "value" field
iscalar["value"] = 42;
// Functionally equivalent pseudo-C++
struct NTScalar_Int64 {
int64_t value;
struct alarm_t {
int64_t secondsPastEpoch;
int32_t nanoseconds;
int32_t userTag
} alarm;
struct time_t {
int32_t severity;
int32_t status;
std::string message
} timeStamp;
// if NTScalar::display
struct display_t {
int64_t limitLow, limitHigh;
std::string description, units;
// if NTScalar::form
int32_t precision;
struct enum_t {
int32_t index;
std::vector<std::string> choices;
} form;
} display;
// if NTScalar::control
struct control_t {
int64_t limitLow, limitHigh;
} control;
// ...
};
auto iscalar = new NTScalar_Int64(); // not safe!
iscalar->value = 42;
Fields¶
- “value”
The primary field. May be any
pvxs::TypeCodeother thanStruct,Union,StructA,UnionA, orNull.
“timeStamp.secondsPastEpoch”, “timeStamp.nanoseconds”, “timeStamp.userTag”
See common time_t.
“alarm.severity”, “alarm.status”, “alarm.message”
See common alarm_t.
- “display.description”
Text providing some context about what this value/PV represents.
- “display.units”
Text identifying units of value. eg. “V” or “Hz”
Meta-data for numeric types.
“display.limitLow”
- “display.limitHigh”
Hints for clients which can indicate inclusive range of possible values. eg. a UI gauge widget. Ignore unless limitLow < limitHigh
“control.limitLow”
- “control.limitHigh”
Hints for clients on the inclusive range of values which may reasonably be written to this PV. Ignore unless limitLow < limitHigh Not authoritative.
“valueAlarm.lowAlarmLimit”
“valueAlarm.highAlarmLimit”
“valueAlarm.lowAlarmSeverity”
“valueAlarm.highAlarmSeverity”
“valueAlarm.lowWarningLimit”
“valueAlarm.highWarningLimit”
“valueAlarm.lowWarningSeverity”
- “valueAlarm.highWarningSeverity”
Hints for clients on the ranges of values which will result in a alarms of the given severities. Could be used by eg. a UI gauge widget to place markers colored by alarm severity. Actual alarms are signals with “alarm.severity”.
Two value ranges are defined. The names Alarm vs. Warning do not have a special significance.
Ignore *Alarm* range unless lowAlarmLimit < highAlarmLimit
Ignore *Warning* range unless lowWarningLimit < highWarningLimit
If a value is within a range [low*Limit, high*Limit] inclusive then no alarm is expected. If a value is < low*Limit then the alarm severity low*Severity is expected. If a value is > high*Limit then the alarm severity high*Severity is expected.
Builder API¶
-
struct NTScalar¶
A scalar, or array of scalars, and meta-data
auto def = pvxs::nt::NTScalar{TypeCode::Float64}.build(); def += { Member(TypeCode::String, "myspecial"), }; auto value = def.create(); // instantiate a Value
Public Functions