, ISTXIESCI CKD I I I X 'F l' I ICCCI Froa IETXI IAddressl I • I ISTXIESCI CKD IWCCISBAIBuff IETXI , 'IX'F1'1 IAdr I I I I I I I (4040 I I • I The following is representative of typical 1nput-to-processor message formats. The format of a multiline read operation follows. • 1/--------------------1/ , IIndexlSTXICU IDevlAIDICursorlSBAIBuffl Text ISBllBuffl Text IETII I Byte I I Adr I Adr I I lddr I I Addr I I Ilddr I I I , 1/ 1/ Another form of input message is the error status message. Error status
is processed by the DKKRGF module. The characters, following the SOB signify that this message contains sense and status data. The format of this message follows • • IIndexlSOHI IByte I I I I I I R ISTXICU IDevlSense/lETI I IADRIAdrlStatusl I I I IBytes I The test request aessage, upon receipt from display terminals, is
ignored by CP. The input inhibit mode that the display terminal enters
upon pressing the test request key can be reset only if the terminal user presses the RESET key. The characters, following SOH indicate
the test request function. The format of this message follows.
Index
Byte SOH I STI Text ETI
1-104 IBK VK/310 System Logic and Problem Deteraination--Volume 1

ALLOCATION MANAGEMENT Real storage space above the Control Program nucleus is made up of the dynamic paging area and the free storage area. Page frames (allocation
space in real storage for a page of data) in the dynamic paging area are
allocated to virtual machines and the control program to satisfy paging
requests. Blocks of storage, requested by virtual machines and CP for
working storage, are allocated from the free storage area. NORMAL PAGING REQUESTS If a program interruption is caused by a normal paging request (not from a virtual Machine that is running in Ee mode with translation on)w DMKPRGIN determines whether a segment or page translation error has
occurred. If one of these errors occurred, an invalid address
interruption code is set, and the interruption is reflected to the
virtual machine supervisor. If a segment or page translation error has
not occurred, the virtual machine's current PSW is updated from the program old PSW (PROPSW), the address of the current VMBLOK is placed in
register 11, and DMKPTRAN is called to obtain the required page. When the paging operation is completed, control is returned to DMKDSPCH. When operating in the CP relocate environment, each virtual machine's virtual storage space is described by two sets of tables. • One set, the segment and page tables, describes the location and
availability of any of the virtual machine's virtual pages that may be resident in real storage. Locations in these tables are indexable
by virtual address, and the entries contain index values that
reference corresponding real storage ·addresses. In addition, each
table entry contains an indication of whether the corresponding
virtual page is available to the user in real storage. These tables are referenced directly by the DAT feature when the virtual machine's program is running. • The second set of tables, called swap tables, is a map of the
locations of the virtual machine's pages on the DASD devices that comprise the system's paging or auxiliary storage. The DISD addresses in these tables can either represent the source of a page
of virtual storage (the location to which a page may be moved if
necessary) or a du.my address, indicating that the given page has not
yet been referenced and, thus, has a value of binary zeros.
The swap tables are arranged in a format indexable by virtual storage
address. In addition to containing the address of a page, each entry
contains flags and status bytes that indicate such information as: • The storage protection keys to be assigned to the page when it is made resident. • Whether the page is currently on its way into or out of the system (in transit), etc.
These tables are not referenced directly by the hardware
page and segment tables, but are used by paging manage.ent user pages that are needed to execute a program. as are the
to locate CP Introduction 1-105