gtpd2m0z | Data Communications Services Reference |
The nature of unit record operations is basically operator oriented and dependent. Therefore, the design and implementation of unit record macro support within the TPF system has to be geared to operator communications and control. Downgrading of the system when using unit record devices could occur due to holding core blocks for long periods of time relative to the time required by other I/O devices; therefore, programs using unit record macros should be run only when downgrading of the system can be tolerated. Because of this external system dependence, it is strongly recommended that jobs involving unit record devices only be run when system activity is low. Application programmers should insert Delay and Defer macros in their code when their use of core is at a minimum since this will allow more important programs to more fully utilize the system; thus, periods of minimum core block holding should be designed into the Application Program if at all possible.
To enable the user to write to a printer or read from a card reader the following macros are provided:
Each unit record device in the system will have a three character symbolic name associated with it. For printers the name must be one of those from PR1 to PR7. For card readers, the name must be either CR1, CR2 or CR3. A feature, called the AVAILABLE device feature, is also supported. The symbolic names PRA and CRA are associated with the available printer and available card reader respectively. If a job requires the use of a certain device type and yet does not have the requirement of a specific device, the AVAILABLE option can be used in the USURC macro and the subsequent unit record I/O macros. In such a case the system will find, upon the user issuing the USURC macro, the first device of that type which can be assigned and associate it with the issuing ECB.
A Unit Record Utility Program (03-CUAL) is provided to perform the following functions: