Configure the data archiver.

Mandatory Arguments:

(none)

Optional Arguments:

Count combine

The number of snapshots from the real-time CPU to combine to form a recorded archive frame.

Wdir dir

The directory in which to place subsequently opened archive files.

Boolean filter

Whether to archive all frames received from the real-time CPU (filter=false), or whether to record only those that have been marked with the mark command.

Count file_size

The number of frames to record per archive file before starting a new file. The default is 0, which tells the archiver to keep writing to the current file indefinitely.

Example 1:

The following example tells the archiver to form archived frames by combining 20 successive register snapshots from the real-time CPU. It also tells the archiver that the next time that a new archive file is created, it should be placed in the /scr/cbi/data directory.

  archive combine=20, dir=/scr/cbi/data

Example 2:

The following example tells the archiver to record individual snapshots from the real-time CPU without combining them, but also tells it not to archive snapshots that haven't been marked as special with the mark command. This will be the normal mode for optical pointing, where one wants to just archive the frames which the user marks as having a pointing star centered on the cross-hairs.

  archive combine=1, filter=true

Example 3:

The following example tells the archiver to start a new archive every time that the current file contains 1000 frames. This keeps the size of each file reasonably small, thus enabling faster access to a given start time when the archive is read.

  archive file_size=1000

Context:

The archiver part of the control program receives snapshots of the state of the real-time system and its hardware, and if asked, records this information to disk. The archive command controls how this is done. It allows one to specify what directory to put archive files in, wether to compress the data by combining a specified number of snapshots and whether to record all combined snapshots or whether to only record those that are marked as special.

The optional combine argument.

The real-time CPU records a snapshot of the state of the system at intervals determined by the interval command. This interval will usually be 0.84 seconds. This is short enough to be useful for those monitoring the state of the system using the cbiviewer program, but if one were to continuously record 12kb snapshots of the state of the instrument at this rate one would end up with enormous files. Thus during normal observing this command will be used to tell the archiver to reduce the size of the files by a factor of 10 by combining every 10 successive snapshots before writing the resulting combined snapshot to disk. The way that the combination is done differs for different registers in the register map. The correlator and receiver tuning card registers are designed with enough headroom for up to 256 snapshots to be coadded before overflow occurs, so these are coadded to increase their signal to noise ratios. Other registers, particularly those on commercial boards are not designed with this in mind, so of each successive 10 snapshots, 9 are discarded and the last is placed in the archived snapshot. The frame.features register, and any other registers that are marked as bit-map unions, are combined by taking their bitwise union. In the case of the frame.features register, this ensures that frame markers aren't lost.

The optional dir argument.

While the directory in which archive files are to be placed can be specified by this command, to explicitly open an archive file you should use the open command.

The optional filter argument.

During optical pointing the observer asks the telescope to track a number of stars, one after the other. On reaching each star, the observer adjusts the azimuth and elevation offsets until the star, as seen through the optical pointing telescope, is centered on the cross-hairs of the TV monitor. At that point he or she presses a button that marks the next snapshot of the system as being a pointing reference frame. To ensure that the marked frame isn't corrupted by being combined with snapshots taken when the telescope is moving to the next source, the archive command should be used to tell the archiver not to combine snapshots into composite archived snaphots. This could result in enormous archive files, so given that one is only interested in those few snapshots that have been marked as pointing reference frames, it also makes sense to tell the archiver to only record marked frames. The second example above shows how this is done.