CL-WEC-TED-xxxx
July 01 2006

SSSC

Issue 1





Prepared by:
CLUSTER DWP TEAM





Department of Automatic Control and Systems Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD

DOCUMENT STATUS SHEET

Prepared by:
CLUSTER DWPTEAM

1.Introduction.

This Release Note for "CL-WEC-TED" CLUSTER WEC Telemetry Extraction & Decommutation Package, describing features,Known Bugs, and Software Changes since the release of TED 2.4.3.

2.Bugs.

The following fixed items are included in this release of TED:

No bugs formally reported. However some code that appeared to free() uninitialised pointers was corrected.

The HKTIM module has been substantially rewritten compared to that included in TED 2.4.3.

Handling of missing HK source packets has been improved.

3.Changes & New Features.

The following items are included in this release of TED:

• CL-WEC-TED-149 WEC science time tag improvement.
• Support for WEC time correction (TCOR) files.
• Full set of ground station identifiers allowed.

3.1. CL-WEC-TED-149 WEC time tagging

A method of correcting time tagging inaccuracies related to the EW5SSOFF parameter and DWP master clock frequency has now been implemented as a component called HKTIM. The component forms an exponential mean of the errors and makes corrections to the parameters.

The HKTIM component has been sited in the UNPACK module, such that only HK being processed by TED may be processed as repeated application of HKTIM is not permitted.

An extension to the UNPACK API enables control of HKTIM from applications. In LEVELONE the user option for this purpose is '-m'.

The Component's and UNPACK's default action is to correct EW5SSOFF and the master clock frequency.

3.2. Support for WEC time correction files

A method of correcting inaccuracies in the Spacecraft Event Time (SCET) placed in the RDM by ESOC has been implement using time correction (TCOR) files.

An environment variable TCOR_PATH is used as the primary method of locating the TCOR files. An extension to the UNPACK API enables this to be overridden from applications. In LEVELONE the user option for this purpose is '-T'.

3.3. Full set of ground station identifiers allowed

TED will now process without errors data having any one of the 16 possible ground station identifiers.

4.Compatibility with previous versions.

4.1. Environment and TCOR files

The TCOR files are normally located using the TCOR_PATH environment variable. This should be defined as the full path of the directory where the TCOR files are located, and must have a trailing /. If no path is specified, data will be processed without corrections and no diagnositic message issued. If an incorrect path is specified (directory does not exist, or TCOR files not found there) a diagnostic message is issued for every HK source packet processed.

The CEF format TCOR files as downloaded from the Cluster Active Archive should be located in the TCOR directory. There should be at least one file for each spacecraft. In addition, for TED 2.5.0, an index file for each spacecraft called TCOR_INDEX_n.txt must be created where n is the spacecraft number. This file must contain the name of each TCOR file for that spacecraft, followed by an ISO_TIME_RANGE variable giving the range of the file. The latter can simply be copied from the TCOR file metadata.

4.2. New LEVELONE options

As mentioned above, the HKTIM control option in the LEVELONE program may be used to modify the operation of HKTIM, in the UNPACK module. The new levelone option is:

-m <mode>

where mode may be an integer from 0 to 3.

The default is 3 which provides most accurate timing. As a result time tags in the DSD files may differ by a few ms from previous versions of TED. For full compatibility with previous versions "-m 1" should be specified.

The TCOR_PATH environment variable may be overridden using the levelone -T option:

-T <path>

If this option is used to specify an empty string (-T "") then TCOR files will not be used, irrespective of the TCOR_PATH environment.

4.3. Additions to the TED API

The function ted_unpack_hktim (int mode) may be used to specify the HKTIM mode in the same way as the levelone -m option.

The function ted_unpack_hktcor (char *path) may be used to specify the path to the TCOR files in the same way as the levelone -T option.

4.4. New bits in DSD diagnostic word

Three new bits have been defined in the DSD diagnostic word.

The TED_DSD_DW_HKTCOR_CORRECTED bit will be set (non-zero) if time corrections from the TCOR files have been successfully applied by TED (or if the RDM files were flagged as pre-corrected).

The two TED_DSD_DW_HKTIM_MODE bits form a two bit code specifying what EW5SSOFF corrections have actually been applied. This may not always be the same as the mode requested using the -m option.

If the default HKTIM mode 3 (running average) is selected, then initially the actual mode used will vary in the range 0 to 2, until a valid running average has been established, then normally mode 3 will be used for the rest of the file.

When all three bits are set (TCOR corrections applied, HKTIM running average) times should normally be accurate to 20  s, although no absolute guarantee can be given. In particular this depends on the accuracy of the source data used to prepare the TCOR files which cannot always be independently verified.

4.5. Missing HK source packets

The detection of missing HK source packets has been improved. Whenever an HK packet is processed, the entry for the following packet is immediately marked empty, to be overwritten if and when the packet is processed. Previously, missing packets were only marked empty after a gap had been detected, that is when the first packet after the gap had been processed. Sometimes this did not occur soon enough to prevent out of date entries in the HK table being used.

If the primary HK packet used to construct the science packet time tag is missing, TED will now use the following packet instead (the one EW5SSOFF and other HK parameters are taken from), and adjust the time accordingly. The diagnostic flag DW_NOHKTIME will be set only if both HK source packets are missing.