Live API VIs
| DataLog Read Last Number.vi | DataLog Read Last String.vi | DataLog Write String.vi | re_DataLog Write Number.vi |
Query API VIs
| DataLog Interpolate Log.vi | DataLog Merge Times.vi | DataLog Read Log Strings.vi | re_DataLog Tag Info.vi |
| DataLog Log Info.vi | DataLog Read Log Index Range.vi | DataLog Read Log Time Range.vi |
API objects
| obj_DataLog Tag Buffers.vi | obj_DataLog Tag Hash.vi |
Reads the last-written number (the current value) from a number tag of the live database. This is a convenience wrapper around the "Tag Buffers" object which provides a more complete set of methods for reading values from a tag's buffer.
|
|
tag Tag name. It is used when "tag index in" is not wired. |
|
|
tag index in (name lookup) The index of the tag. If left unwired or less than zero, a tag lookup will be performed, and the related inputs must be wired. When performing repeated actions on the same tag, use a shift register initialized to a negative value (e.g. -1) around the tag index in/out. This will cause the first iteration to do a name lookup, and subsequent iterations to use the tag's index. |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
number Number value read from tag. |
|
|
time Timestamp of the number value. |
|
|
tag index out Duplicate of "tag index in", if wired. When "tag index in" is left unwired, this returns the index of tag "tag", or -1 when an invalid name is wired to "tag". |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Reads the last-written string (the current value) from a string tag of the live database.
|
|
tag Tag name. It is used when "tag index in" is not wired. |
|
|
tag index in (name lookup) The index of the tag. If left unwired or less than zero, a tag lookup will be performed, and the related inputs must be wired. When performing repeated actions on the same tag, use a shift register initialized to a negative value (e.g. -1) around the tag index in/out. This will cause the first iteration to do a name lookup, and subsequent iterations to use the tag's index. |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
string String value read from tag. |
|
|
time Timestamp of the string value. |
|
|
tag index out Duplicate of "tag index in", if wired. When "tag index in" is left unwired, this returns the index of tag "tag", or -1 when an invalid name is wired to "tag". |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Writes a string value to a tag. The current time is used as timestamp if no custom time is wired. The current database must be live.
|
|
string The string to write to the tag. |
|
|
time (current) Timestamp to apply to the string value being written. When not wired or NaN is wired, the current time is used as timestamp. |
|
|
tag Tag name. It is used when "tag index in" is not wired. |
|
|
tag index in (use tag) The index of the tag. If left unwired or less than zero, a tag lookup will be performed, and the related inputs must be wired. When performing repeated writes to the same tag, use a shift register initialized to a negative value (e.g. -1) that loops "tag index out" back to "tag index in". This will cause the first iteration to do a tag name lookup, and subsequent iterations to use the more efficient index. |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
tag index out Duplicate of "tag index in", if wired. When "tag index in" is left unwired, this returns the index of tag "tag", or -1 when an invalid name is wired to "tag". |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Writes a number value to a tag. The current time is used as timestamp if no custom time is wired. The value is checked against any limit meta tags and coerced to any max/min meta tags. The current database must be live.
|
|
number The number value to write to the tag. |
|
|
time (current) Timestamp to apply to the number value being written. When not wired or NaN is wired, the current time is used as timestamp. |
|
|
tag Tag name. It is used when "tag index in" is not wired. |
|
|
tag index in (use tag) The index of the tag. If left unwired or less than zero, a tag lookup will be performed, and the related inputs must be wired. When performing repeated writes to the same tag, use a shift register initialized to a negative value (e.g. -1) that loops "tag index out" back to "tag index in". This will cause the first iteration to do a tag name lookup, and subsequent iterations to use the more efficient index. |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
tag index out Duplicate of "tag index in", if wired. When "tag index in" is left unwired, this returns the index of tag "tag", or -1 when an invalid name is wired to "tag". |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Interpolate the point values in a tag log at the specified times. When the tag is of "sample" temporal type, the values of the two points adjacent to each specified time are linearly interpolated in case of a number tag, or, in case of a string tag, an error is returned. When the tag is of "set&hold" temporal type, the value of the last point prior to each specified time is used: such tags hold their value until changed. In case of a string tag you'll have to use the returned offset values to read the string values from the log. When the tag is of "event" temporal type, an error is returned since such tags have values that are defined only at the time of the event.
Note that this VI tries to read the timerange covered by the specified times from the tag log before commencing with interpolation. This fails when the timerange contains more than "max points" points. In such an event, the specified times are divided in increasingly smaller chunks until the reads succeed. In this eventuality, it helps performance when the specified times increase or decrease monotonically.
|
|
tag log directory |
|
|
tag config Wire the temporal type of the tag here. |
|
|
name |
|
|
unit |
|
|
temporal |
|
|
value |
|
|
index |
|
|
capacity |
|
|
is meta? |
|
|
mincapacity |
|
|
deadband |
|
|
limit delay |
|
|
format |
|
|
precision |
|
|
undefine |
|
|
update |
|
|
update period |
|
|
expression |
|
|
description |
|
|
logging algorithm |
|
|
logging parameters |
|
|
|
|
times The times to interpolate at. |
|
|
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
dup tag log directory |
|
|
value type Value type of the tag. In case of "string", the returned offset values must be used to retrieve the actual string values. |
|
|
interpolated values Point values interpolated (linearly or held from prior) at the specified times. |
|
|
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Returns the log size, that is, the number of values (numbers or strings) contained in the tag's log. Since, on writing, logs are only appended to, this equals the write index. A double is used because it can represent very large integers without overflowing or rounding. In addition, the start time, that is, the timestamp of the first logged point is returned. When the log is empty, the start time is set to NaN.
|
|
tag log directory |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
dup tag log directory |
|
|
size Number of values in the log. |
|
|
start time Timestamp of the first logged point. |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Merge times for interpolation. Given two arrays of monotonically increasing times, output an array of times that contains the monotonically increasing union of the input times. When the time arrays contain identical values, the value is copied only once into the output array.
Beware that when either set of times does not increase monotonically, the output times will not either. Though sorting the times is not difficult, this option was rejected to ensure that the algorithm executes in linear time: the arrays might be very large.
|
|
times to add |
|
|
|
|
times in |
|
|
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
times out |
|
|
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Read the range of points starting at the specified index from a tag's log.
|
|
tag log directory |
|
|
log index Index of first point to read. |
|
|
number of points Number of points to read. When more points are requested than the configured "max points", and error is thrown. |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
dup tag log directory |
|
|
range of points |
|
|
|
|
time |
|
|
value |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Read the strings at the specified byte offsets from the strings file of a string tag log. These offsets are stored as the values of the tag's point. Consequently, to use this function, you must pass a range of points read from the tag's log or their offset values.
|
|
tag log directory |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
points (use offsets) |
|
|
|
|
time |
|
|
value |
|
|
offsets (use points) |
|
|
|
|
dup tag log directory |
|
|
strings |
|
|
string |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
|
|
times The timestamps of the provided points (if any). |
|
|
Read a range of points that covers the specified time range from a tag's log. The first returned point's time <= begin, the last returned point's time >= end. An exception to this rule occurs when the range begins before the oldest point in the log or ends after the last point in the log. In that case as much data as possible will be returned. If the range lies before the logged data, only the first point will be returned. If the range lies beyond the logged data, only the last point will be returned.
|
|
tag log directory |
|
|
begin of range |
|
|
end of range |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
dup tag log directory |
|
|
too many points? True when the VI failed because there were more than "max points" in the specified time range. |
|
|
time range of points |
|
|
|
|
time |
|
|
value |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Return information on a tag in a database. The returned tag log directory can be used to perform queries on the tag's log. The returned tag config cluster can be used to determin the temporal type, value type, or unit of the tag.
The tag can be specified via its name, or via its index. In the latter case the database must be live. The database can be specified via a reference or name. When omitting both, the current database is used.
When true is wired to the flush input, an attempt will be made to flush the buffered tag data to the log before returning. Use this when you are about to query data from the log and require the most recent available data. Note that flushing propagates over the network for a mirrored database provided that a mirroring connection has been established.
This VI is reentrant not only because flushing might take some time, but also to avoid recursion deadlocks when the database being mirrored is part of the local runtime (e.g. for testing purposes).
|
|
database ref (use name) Reference to the database object instance. Provides an alternative means of specifying the database. |
|
|
flush? (false) When you need the most recent available data to be present in the tag log, wire true. When the database is live or being mirrored, any buffered data to the tag's log. |
|
|
database (current) Used when no database reference is wired. Specifies the name of the database. When left empty, the current database is used. |
|
|
tag Name of the tag. Used when the database is not live or no tag index is wired. |
|
|
tag index (use tag) The index of the tag for which to contstruct the tag log directory path. Only works when the database is live. |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
tag log directory The directory containing the tag's log. This can be be wired into subsequent query VIs so as to read or interpolate the log. |
|
|
tag config Tag configuration cluster. |
|
|
name |
|
|
unit |
|
|
temporal |
|
|
value |
|
|
index |
|
|
capacity |
|
|
is meta? |
|
|
mincapacity |
|
|
deadband |
|
|
limit delay |
|
|
format |
|
|
precision |
|
|
undefine |
|
|
update |
|
|
update period |
|
|
expression |
|
|
description |
|
|
logging algorithm |
|
|
logging parameters |
|
|
|
|
mode Mode of the database. |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Provides circular buffers for the tags in the live database. Only the {read} and {read last} methods are intended for public use. All other methods are private.
The implementation pools the tag buffers so as to provide indexing over tags while avoiding more complicated composite data structures that confuse the LabVIEW compiler sufficiently to not to generate in-place code. By restricting the tag buffers in the pool to have a power of two capacity, modulo the capacity reduces to a simple bitwise "and" operation with a mask, and a write or read index overflow (at 2^31) does not invalidate the indexing. To make comparisons of indices overflow insensitve, their difference is compared to zero.
|
|
method Public methods: {read} read a point from a tag buffer at the specified index. The returned read index is incremented. {read last} read the last point written to a tag buffer. The returned read index can be used to {read} the next point to be written. Private methods: {inert} internal method used to do nothing when the tag index is invalid. {write} write a point to a tag buffer. This method is private since the public write interface is provided by the "Write Number" and "Write String" VIs. {read oldest} read the oldest point still stored in a tag's buffer. Note that subsequent points are not guaranteed to be present during subsequent reads since writes might have occurred in the mean time. Thus, getting the maximum amount of data requires a bit of care. See for example the "Dump Tag Buffer" VI. {initialize} initialize the buffer pool and other internal state using information stored in the tag info list object. {cleanup} dispose of the buffer pool and other internal state. |
|
|
read index in {read} the index at which to read a datapoint from the tag's buffer. |
|
|
point in {write} The datapoint to write to the buffer. |
|
|
time |
|
|
value |
|
|
tag index {initialize} {cleanup} not applicable. Other methods: the index of the tag to which the buffer method is to be applied. |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
available? {read} is the indexed point available? If false, the requested point has not yet been written. It might also be that the requested point is no longer available in the buffer, in which case an error will be returned. {read last} is the last point available? If not, an error will be returned. {read oldest} is an oldest point available? If not, an error will be returned. |
|
|
read index out {read}, {read oldest}, {read last} points to the next point in the buffer or to be buffered provided that the read point was available. Otherwise it points to the point for which the failed read attempt was made. other methods: dup of read index in. |
|
|
point out {read} {read oldest} {read last} that point read from the buffer. Other methods: duplicate of point in. |
|
|
time |
|
|
value |
|
|
tag index dup Duplicate of tag index in. |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
Efficiently associates the names of the tags in the live database with their indices. A tag index is required to access tag-specific data inside data structures set up for the live database. Only the {index tag}, {lookup}, and {#tags} methods are meant for public use. The {index tag} method retrieves the tag's name given a tag index. The {lookup} method retrieves the tag's index given a tag name. The {#tags} method returns the number of tags in the live database.
By storing the tag indices in a hash table, a lookup of a tag's index via its name becomes an O(1) operation (the execution time is independent of the number of tags). In this way, the amount of work during repeated run-time operations is reduced by proper preparation during the once-only initialization.
NOTE: the subVIs for accessing the live database mostly accept both tag indices and tag names. In the latter case, they use this object to {lookup} the tag index.
|
|
method Public methods: {index tag} retrieve a tag by its tag index. {lookup} retrieve a tag index by its tag. {#tags} return the number of tags in the live database. Private methods: {initialize} initialize the hash and other internal state. {add tag} add a tag to the hash and assign an index. {cleanup} dispose of hash and other internal state. {write recovery} write the internal state to disk so as to allow it to be used to recover from a crash. This should be called once all tags have been added. {read recovery} attempts to recover the hash state from disk so that the crash recovery can commence. Crash recovery mostly entails flushing the content of the recovery file. This requires an indexable list of tags. When the system was shut down properly, this function returns an error since the recovery file will have been deleted. {delete recovery} deletes the recovery file. This prevent a recovery from occurring during the next system startup. It should be called after the aggregation buffer has been fully flushed on shutdown. |
|
|
tag in {add tag}: will be added to the hash table. {lookup}: used to look up the tag's index. |
|
|
tag index in {index tag} the tag whose name must be retrieved. |
|
|
error in (no error) When an error is passed in, this VI will return without executing its actions. |
|
|
#tags |
|
|
tag out {index tag}: the tag with the given index. |
|
|
tag index out {lookup}: the named tag's index. {add tag}: the assigned tag index. Other methods: a duplicate of "tag index in". |
|
|
error out Returns the input error or any error that occurs on execution of this VI. |
