gtpi1m54 | System Installation Support Reference |
The tape display user exit, UXTD, is called to set up message displays for tape devices supported by TPF 4.1. A message is displayed until it is changed by another Load Display (LDD) command or until the cartridge is physically unloaded. Therefore, UXTD is called at mount, dismount, and tape switch time (to reset the display if the tape is not unloaded).
The message display is set up in the SETUP subroutine, which can be modified. This should be the only code modified in UXTD. On return from SETUP, the calling routine will issue a Load Display command to display the messages set up by this routine.
UXTD is called by the following segments:
Input
The following registers are used by the SETUP subroutine:
The contents of R7 through R15 are expected to be unchanged on return from SETUP.
Data Structures
DSECT LDDAREA maps the data portion of the LDD CCW that will be sent to the tape device. This area consists of the following fields:
The 2 message areas, LDDMSG1 and LDDMSG2, are each 8 bytes. Both are
initialized to zeros when SETUP gets control.
Table 5. The Byte Arrangement for Message Display
Message 1 | Message 2 | Display |
---|---|---|
Zeros | Zeros | LDD not issued |
Nonzeros | Zeros | Message 1 only |
Zeros | Nonzeros | Message 2 only |
Nonzeros | Nonzeros | Alternating Message 1/Message 2 |