Processing description of the log processor

The Log Processor is activated by the Communications Source program when one of the following conditions exists as specified by indicators in the WGTA entry associated with the terminal inputting the data:
  • The terminal is in IDLE state (currently not connected to any application).
  • The sign-in-process indicator is set in the WGTA and the first 3 characters of the input text are equal to LOG.

The following information introduces the concepts of screen formatting as it relates to the 3270-type terminals.

Display data, print data, or control data that is sent from the CPU to a 3270-type terminal is received and formatted at a control unit buffer and is then transferred to the device buffer. Conversely, display or print data that originates at a device is first sent to the control unit buffer, prepared for transmission, and then sent to the CPU.

A 3270 terminal can operate in one of two basic modes:
  1. With an unformatted display in which no attribute character (and, therefore, no display field) has been defined. The terminal is used in a free-form manner similar to the IBM® 4505.
  2. With a formatted display in which a display field (or fields) has been defined as a result of storing at least one attribute character in the display buffer. The attribute characters define data fields with such characteristics as: protected (fixed format), unprotected (variable input data), alphameric input, selector pen detectable, and so on.

As a result of operating in one of the previous modes, the input data sequence assumes different aspects. The presence of a set buffer address code (SBA) following the cursor address in the input data identifies the data sequence as being formatted. This knowledge is necessary to the Log Processor to be able to perform textual interpretation on the incoming data. (All the details relative to the 3270 terminal characteristics, functions and programming will be found in the referenced literature.)

In summary, the Log Processor has to be able to interpret data sequences input at non 3270-type terminals, and formatted or unformatted 3270-type terminals. Different components of the Log Processor analyze input data depending on the type and status of the terminal (these characteristics are reflected in the terminal's WGTA entry). This logic is schematically represented in Figure 1.
Figure 1. Log processor overview (LOGI/LOGO message processing)
Information about Figure 1
Step 1:
The format of the message is identified by analyzing the type of terminal and, if a 3270-type, the mode of operation (4505 simulation or native mode). Invalid Log messages are discarded and the inputting terminal notified. All messages sent by the Log Processor are transmitted by activating a component of the System Message Processor (03-CSMP).
Step 2:
The application name specified in the Log message is located in the RCAT table and its validity is verified. This is done by checking the application status.
Step 3:
For terminals requiring authorization through the application list, the Terminal Application Authorization Record (TAPP) is retrieved and scanned. The application requested is verified by locating the supplied name in the terminal's Authorization List.
Step 4:
The WGTA entry is updated to record the connection of the inputting terminal to the requested application.
Step 5:
A response notifying the inputting terminal of a successful log is then generated and transmitted to the terminal.

LOGU and LOGP messages are processed as in Steps 1, 2, and 3 before activating the Unsolicited Message Processor which will execute the requested function.

Some applications are classified as requiring sign in/out procedures. This requirement is recorded in the RCAT table at the entry relative to the specific application.

In summary, the most important function of the Log Processor is to store the requested application reference in the WGTA. This is key to the entirez/TPF -MR structure since this application name is used by the Communications Source Program to build the Routing Control Parameter List, which is in turn used by the Router program to find a path for the data from the terminal to the application.