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This section describes the preliminary design of the ACIS Back End's Detector Electronics Assembly Housekeeping software. This software is responsible for periodically acquiring and sending housekeeping information from the Detector Electronics Assembly.
Figure 15 illustrates a coarse overview of DEA Housekeeping operations, where the numbers indicate the overall sequence of operations.
FIGURE 15. DEA Housekeeping Overview
All parameters which select and control DEA Housekeeping operations are supplied by ROM or by parameter blocks loaded by command into the Back End Processor. The Back End software encapsulates the top level representation of parameter blocks using a "DEA Housekeeping Parameter Block" class, which is a subclass of "Parameter Block" (see Section 11.3.1 on page 66). This type of parameter block "enhances" the top level representation by providing access to application-specific fields within the block. Table 48 lists the operations added by the DEA Housekeeping block subclass.
TABLE 48. `DEA Housekeeping Parameter Block'Operations
------------------------------------------------------------------------------------------ Function Inputs Outputs------------------------------------------------------------------------------------------ Get Sampling none The rate, in TBD units, to sample, acquire and tele Period meter a single DEA Housekeeping Packet. Get Number of none Returns the total number of DEA Housekeeping Entries entries contained in the parameter block. Get Entry Entry Index Returns the DEA Housekeeping entry located at "Entry Index" within the block. Load from Com Address of a DEA none mand Packet Housekeeping Com mand Packet, which contains the new DEA Housekeeping Parame ter block contents. ------------------------------------------------------------------------------------------
All DEA Housekeeping Parameter blocks within the Back End are contained in an array of "DEA Housekeeping Parameter Blocks." The "block id" serves as an index into the array. The length of this array is TBD and the first TBD elements are loaded at startup from the Back End Software ROM. The Back End software encapsulates this representation using a "DEA Housekeeping Block List" class. This class is a subclass of "Parameter Block List," described in Section 11.3.2 on page 67. The operations provided by "DEA Housekeeping Block List" are the same as those provided by "Parameter Block List," except the argument and return types of the parameter block are to a "DEA Housekeeping Block List" instance.
The Back End software manages an overall DEA Housekeeping Run using the operations provided by a "DEA Housekeeping Run" class. This class is responsible for fetching the parameters for a run, periodically acquiring and storing the requested information from the DEA, and for posting the "DEA Housekeeping Telemetry Packet" to the Telemetry Manager. The operations provided by a "DEA Housekeeping Run" are listed in Table 49.
TABLE 49. `DEA Housekeeping Run'Operations
--------------------------------------------- Function Inputs Outputs--------------------------------------------- Initialize none none Set Verbose Mode none none Set Terse Mode none none Execute Run Parameter Block Id none Shutdown Run Parameter Block Id none ---------------------------------------------
The Back End software uses "DEA Housekeeping Telemetry Packet" class to store and telemeter acquired DEA Housekeeping values. This is a subclass of a "Telemetry Packet," which provides the operations needed to telemeter the information. The "DEA Housekeeping Telemetry Packet" class provides the additional operations listed in Table 50.
TABLE 50. `DEA Housekeeping Telemetry Packet'Operations
---------------------------------------------------------------------- Function Inputs Outputs---------------------------------------------------------------------- Initialize DEA Acquisition Id none Reset Item Count none Zeros the item count in the packet. Get Max. Item Count none Returns the maximum num ber of items which can be held by the packet Get Available Space none Returns the space remaining in the packet. Add Item Item Id Stores the specified item id Item Value and value in the next avail able slot in the packet. ----------------------------------------------------------------------
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