Description of Symbol Table Database Elements

1- Symbol Name

This is the root name of the symbol. This name is used to create names for shared variables, message variable, several functions, and #defines. This symbol name should be unique to all other symbol names.

2- Data Type

This element describes the C code data type. Standard C data types and structures are used in the symbol table. Data structures are cataloged within the data structure database.

3- Array Size

The size of the array is given in this field. If no array size is displayed than that symbol is not an array. Multidimensional arrays are not used in the symbol table, either a single variable or a one dimensional array will be defined.

To keep the symbol table small, arrays are used to designate different arm systems.

 Example

short armStatus[MAX_ARM]

This variable could hold the status of each of Ranger's arms. This allows for the symbol table to remain small since each arm system has similar information. The MAX_ARM macro is a special case which cases several special functions to be used to allow for

Each armStatus to be sent independently. Another macro should be used if the entire array will be sent in one message.

4- Units

This field displays what units are used in the values of a symbol. For structures or arrays, different units may be defined for the different elements of the structure.

5- Subsystem

This is the name of the subsystem that a symbol is group in. These groups hold several symbols which are related to each other in functionality or type of system they control. These subsystem names are used as define flags for a computer project with allows that application to use only the symbols it needs, ignore the rest of the symbol table. The Search page allows a user to pick from the list of all current subsystems and find the symbols associated in those groups. A description for each subsystem can be read. Each variable is associated with only one subsystem.

6- RCL Message

This is the root name used to create message specific names to communicate information using RCL (Ranger Comunication Library). If NDDS is not used this element is not necessary. The RCL message name is derived from the subsystem name. If the last character in the name is a number, than the message is characterized as a command. Commands are typically messages sent from a control station to a robotic vehicle. Telemetry messages is denoted when the last character in the RCL message name is a letter. Telemetry is defined as messages from the robotic vehicle to a control station. All symbols are characterized as one of the above two groups, although some messages do not exactly fit into those groups.

 Example 1

CDxl2_1
CDxl = Left Dexterous arm system
2 = The second group within the Dexterous arm communications
_1 = The first command message
 
The originated subsystem = CDxl2

Example 2

CBus1_B
CBus = Ranger Bus system
1 = The first group within the Bus system communications
_B = The second telemetry message
 
The originated subsystem = CBus1

7- Symbol Value Info

Each symbol is related to a message which holds a variable. The ranges and typical values of the variable are given in the Symbol Value Info box. Each field with in the box is described below:

 Default Value:  This is the original value which is initialized with the variable
 Minimum:  This is the minimum value which the variable will obtain. Below this value an error has occurred.
 Lower Red Warning:  This is the lowest operational warning threshold for the variable. Below this value the operator will be notified that an error has occurred.
 Lower Yellow Warning:  This is a low operational warning threshold, below this value the operator may be notified of the warning.
 Upper Yellow Warning:  This is an upper operational warning threshold, above this value the operator may be notified of the warning.
 Upper Red Warning:  This is the highest operational warning threshold for the variable, above this value the operator will be notified that an error has occurred.
 Maximum:  This is the maximum value which the variable will obtain. Above this value an error has occurred.

8- Data Rate

The data rate is the frequency, in Hertz, that the message is transmitted.

UDP_RATE Macro is used to denote that this variable is transimitted at the default communication rate, currently defined at 25 Hz.

TCP_RATE Macro specifies that the variable is an event message, only sent deliberately when a change in the status has occured or a desired action should be taken.

9- Symbol Type

As described before, symbol's are split into two categories: command and telemetry. Command symbols are typically sent from a control station to a vehicle system. Two types of command symbols exist, command and non flight. Telemetry symbols are sent from the vehicle to be displayed on a control station. Although some symbols do not exactly fit perfectly into these categories, all are defined as one or the other. The symbol type field display which category a symbol is. For telemetry symbols, more designation is required. There are three groups which telemetry fall under: derive, verify, and raw. The table below describes each symbol type designation.

 Command  A symbol sent from a control station module to a system to command some part of that system.
 Non Flight  This command is used in development and academic testing, but is not a command which can change the status of the Flight vehicle.
 Derive  The most common telemetry symbol sent from the computer on-board a system to a control station module.
 Verify  A telemetry symbol used as a receipt of an incoming command symbol. This symbol echoes the associated command back to the control station.
 Raw  A telemetry symbol which was read from memory on board a system. These raw symbols are typically direct readings from sensors. No conversions or any manipulation has been performed on a raw symbol, once a conversion occurs that symbol is deemed a derived symbol. Raw symbols are used to debug hardware by looking at what is being read from hardware into memory.

 

10- Description

A description of that symbol is given which explains the purpose of the symbol and how it is used. If the symbol is an array or structure, each element of the array or structure is summarized as well.