AM3270/TR3271 Reference Manual

Using Multiple-Level Access Methods
A Closer Look at TR3271
5–14 086705 Tandem Computers Incorporated
plus the required additional communications characters. When the host selects a
subdevice with a READ request pending, TR3271 requests a buffer equal in size to the
record size that was defined for the communications line during system generation.
When the application’s request has been completed due to successful transfer or an
unrecoverable error, the buffer is returned to the pool.
As a result, at certain times TR3271 will have only its dedicated buffer available to it.
There are times, however, when TR3271 will have more than one buffer from the pool
available to it.
Level 4 Protocol A subdevice attached to a TR3271 line is a logical entity that receives file-system
requests from an application process. For example, when a subdevice is added to a
TR3271 line using the SCF ADD command, the user specifies a name and the attributes
that define the operating mode.
A subdevice name is in the form of #name, where the # character has significance to
the file-system. Subdevices are referenced by application processes through a
standard Tandem file name. This name consists of the line name and the subdevice
name.
An example of a call to the OPEN procedure is as follows. (The letter b is a blank.)
INT .TNAME[0:11] := [ “$TRLINEb#TERM1bb” , [ 4 * “bb” ] ]
, TERMNO;
TNAME[0:3] = $TRLINEb
is the line name associated with the TR3271 process.
TNAME[4:7] = #TERM1bb
is the name of the subdevice added by the user through SCF.
TNAME[8:11] = bbbbbbbb
is a filler and must be specified.
To open #TERM1, the application process might contain the following statements:
CALL OPEN( TNAME, TERMNO, ...);
IF <> THEN do error processing
If the OPEN is successful, TERMNO is set to the file number assigned by the file
system. Subsequent requests by the application process use TERMNO when
referencing the subdevice.
The specific mode in which a subdevice operates is determined by the level 4 protocol
assigned to it by the user.