AM3270/TR3271 Reference Manual
AM3270Specific FileSystem Operations and Procedures
A Closer Look at AM3270
086705 Tandem Computers Incorporated 3–3
AM3270 makes it possible for the application process to issue requests to terminals
without concern for low-level communications-related line characteristics.
AM3270-Specific
File-System
Operations
Table 3-1 summarizes the file-system procedures that can be used by an application
process as requests to AM3270.
However, note that some of the level 4 subdevice protocols do not allow the use of all
of the procedures listed below. For information on which procedures are allowed,
refer to Section 4, “AM3270 Subdevice Protocols.”
Table 3-1. Applicable File-System Procedures for AM3270
Procedure Action Performed
AWAITIO waits for completion of an outstanding I/O operation.
CANCEL cancels an outstanding request.
CANCELREQ cancels an outstanding request that is identified by a file number and a tag.
CLOSE terminates access to a subdevice.
CONTROL performs forms operations for line printers (see PRT Protocol in Section 4)
and initiates two-step READs (see CRT Protocol in Section 4).
DEVICEINFO returns the type and configured record length for the requested subdevice
or line.
FILEINFO returns error information and characteristics of an open subdevice.
OPEN establishes communication with a subdevice. A subdevice may be opened
up to seven times simultaneously.
READ solicits data from a subdevice. A call to READ causes AM3270 to initiate
polling of the subdevice.
When a subdevice responds to the poll by sending a message, polling is
halted and the subdevice message is returned to the application process
(thus completing the READ).
AM3270 acknowledges the message with the proper ACK0, ACK1, RVI
sequence.
Note: Polling can be initiated by a SETMODE 53, Enable Status Receipt.
SETMODE establishes certain device-dependent operations.
SETMODENOWAIT sets device-dependent functions in a nowait manner, on nowait files.
SETPARAM with SETMODE, sets the value of 32-bit break tag.
WRITE transmits data to a subdevice. The message associated with the WRITE is
transmitted when the subdevice acknowledges the selection.
WRITEREAD behaves as if it were a WRITE request followed by a READ request was
issued by the application process. WRITEREAD is used only by the
interactive terminal interface (ITI) protocol in conversational mode.
Poll/Read Operation Polling is initiated when an application process calls the READ procedure. Poll-list
management is completely under the control of AM3270 and is not accessible to the
application process.