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12.0 DEA Housekeeping

12.1 Overview

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

12.2 Housekeeping Configuration

12.2.1 Housekeeping Parameters - Class "DEA Housekeeping Parameter Block"

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.                                                         

12.2.2 DEA Parameter Library- Class "DEA Housekeeping Block List"

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.

12.3 Setup and Processing Control

12.3.1 DEA Housekeeping Control- Class "DEA Housekeeping Run"

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     

12.4 Data Representation

12.4.1 DEA Housekeeping Data - Class "DEA Housekeeping Telemetry Packet"

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    
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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