THE NPT LINE MONITOR ROUTINE: LINEIO The IPT line monitor routine, LINEIO, controls co •• unications on the BSC line. This rcutine sends and receives data over the ESC line. When the data is received from remote stations, that data is received in the LINEINB buffer. When data is transmitted to a remote station, it
is transitted using the LINEBUFF buffer. The IPT buffers are a fixed
size, defined by terminal type and buffer size specified on the SIGleR card.
THE NPT FUNCTION SELECTOR ROUTINE: NPTGET When the NPT line driver program has been loaded and initialized. the NPTGET program begins a cycle in which it checks every three seconds fer
one of three functions to perform: • Process a command • Read a file from a remote station • write a file to a remote station When a function is requested, a branch is taken to the appropriate
routine. 8PT INPUT FILE PROCESSING For files being received from remote stations, two processing routines
are executed: POTVRFY and PUTBLOCK. PUTVRFY reads the data contained in
the input buffer (LINEINB) and verifies the ESC control characters for
that data. POTBLOCK deblocks the data in LIBEIBE, formats it for use by VM/370, and then writes the data to the VM/370 spool system. NPT OOTPUT PROCESSING ROUTINES For files being transmitted to a remote station, three processing
routines are executed: MAKEBLOC, GETBLOCK, and GETVRFY. MAKEBLOC accepts a block of data from the VM/370 spool syste. and
passes control to GETBLOCK. GETBLOCK then builds a buffer with which to
transmit the data and transmits the data to the remote station. The
response received from that transmission is analyzed by GETVRFY. Major Data Areas
The major data areas used by RSCS are: • SVECTORS • RSCS supervisor queue elements • KAINMAP • TAREA • LINKTABL • TAG • RSCS request elements • VM/370 data areas referenced by RSCS 3-18 IBM VM/370: System Logic and Problem Determination--Volu.e 3

The data areas discussed below give a brief functional overview of each data area and its relationship to other data areas in the system.
This is not meant to be a comprehensive description of the RSCS data
areas. Rather, it is meant as an introduction to the types of data used by RSCS in Ferforming its various functions. SVECTORS: SUPERVISOR CONTROL QUEUES AND SUPERVISOR ROUTINE ADDRESSES The SVECTORS DSECT contains: 0 The PSi the last task dispatched • The RSCS System Save area • The task ID and task element address for the last task dispatched • pointers tc the Rses supervisor subqueues • Entry addresses for all supervisor service routines
This data area is updated dynamically as tasks execute and is used by RSCS to monitor the execution status of the system. RSCS SUPERVISOR QUEUE ELEMENTS All supervisor status information pertaining to tasks and task requests
is maintained in Supervisor storage defined by the SVECTORS DSECT. There are various queues defined in this DSECT, each pertaining to a
particular Supervisor function, and composed cf elements of similar
format. The heads of these queues are defined in a portion of SVECTOES from FREEQ through GIVEQ. The DSECTS defining the elements chained cn
these queues are: FREEE, TASKE, IOE, ASINE, and GIVEE. MAINMAP: STORAGE AVAILABLE TO RSCS PROGRAMS AND TASKS The MAINMAP DSECT is a grid of a fixed number of bytes
E each of which
represents a page of virtual storage. When a task (or the Supervisor) requests storage, the byte is filled with the TASKIt (generated by the Supervisor) of the requestor, thus marking the storage page as taken by that task. When a page is free, its map entry is cleared to zero by the
task owning the storage.
TAREA: THE SAVE AREA FOR AN INTERRUPTED TASK The TAREA DSECT contains the PSi at which a task is to resume execution,
the contents of the task general registers when it was interrupted; and
the task's request synchronization lock. This area is used to maintain
the status of a task when it is interrupted by another task.
LINKTABL: LINK DESCRIPTION DATA
The LINKTABL DSECT describes control data associated with each link in
the system. The control data includes such information as the linkid cf
the link, the task ,name for the link's line driver (that is, the name by RSCS Introduction 3-19