2.3. Configuration

Cascade DataHub™ for Linux and QNX : Version 5.4
	Chapter 2. Using the Cascade DataHub

The Cascade DataHub can be configured with a configuration file at startup, or dynamically during runtime. The commands used for configuration are listed in the Command Set reference, but are not yet documented in detail. The most commonly-used commands are:

alive tells the Cascade DataHub that the client is running.

bandwidth_reduce reduces the connection bandwidth.

domain identifies the client domain name.

enable_dde_client enables or disables DDE client capabilities.

enable_dde_server enables or disables DDE server capabilities.

enable_mirror_master enables or disables mirror master capabilities.

enable_mirror_slave enables or disables mirror slave capabilities.

enable_opc_client enables or disables OPC client capabilities.

enable_opc_server enables or disables OPC server capabilities.

enable_tcp_server enables or disables TCP server capabilities.

heartbeat establishes a heartbeat message.

ignore ignore a given point.

register_datahub registers the Cascade DataHub on a given domain.

request requests the value of a point.

request_initial_data gets current data when client connection is made.

timeout suspends data flow.

2.3.1. Using a Configuration File at Startup

The Cascade DataHub can read a configuration file at startup, using the -f option. The commands in the configuration file are written using Lisp syntax. This consists of the name of the command, followed by a space-separated list of arguments, all enclosed in parentheses, like this:

(command arg₁ arg₂ arg₃ ...)

The commands are commonly written one per line. Comments are denoted by a semicolon (;) at the beginning of each comment line. For example:

; This line is a comment.
(tcp_service 4601)
(enable_tcp_server 1)
(enable_mirror_master 1)

2.3.2. Dynamic Run-Time Configuration

There are several ways that the Cascade DataHub can be configured or reconfigured dynamically during run time:

Using the lsend or gsend command-line tools. These two commands are similar, except one uses Lisp syntax, as explained above, while the other uses Gamma syntax. Please refer to the lsend documentation in the Cogent C API manual for more information.
Here is an example using lsend:
1. Start the DataHub and declare the example domain.
```
[sh]$  datahub -d example
```
2. Start lsend using the name of the DataHub. This consists of the string /dh/ followed by the domain name. If no domain is declared, the DataHub takes its name from its PID. Please refer to Section 2.4.3, “Domains and Names” for more information.
```
[sh]$  lsend "/dh/example"
/dh/example>
```
  When lsend starts it gives you a prompt with the name of the receiving program in it.
3. At the prompt generated by lsend, send commands using the Lisp syntax explained above:
```
/dh/example> (alive)
(success "alive")
/dh/example> (heartbeat 200)
(success "heartbeat" "200")
/dh/example>
```
  For each command, lsend displays the return value from the DataHub in Lisp syntax.
Here is the same example using gsend:
```
[sh]$  datahub -d example
[sh]$  gsend "/dh/example"
/dh/example> alive;
(success "alive")
/dh/example> heartbeat (200);
(success "heartbeat" "200")
/dh/example>
```
The return values for gsend from the DataHub are in also in Lisp syntax.
Sending a command from a C program. The Cogent C API has functions that allow you to send configuration information to the Cascade DataHub. These are explained in the Communicating with the Cascade DataHub section of the Cogent C API manual.
Using the Gamma send and send_async functions. Cogent's Gamma programming language uses these two functions to send commands to the Cascade DataHub and other Cogent products. Please refer to send and send_async in the Gamma manual reference for more details.


2.2. Testing the installation		2.4. Working with Data