CP Program Organization
Use of the Annotated Flow Diagram
The following text sections, which describe each major CP function, are
annotated flow diagraBs. These diagrams, consisting of logic labels and commentary, describe the general flow and use of CP logic modules and
their relationship to other modules while performing a specific function
or task. The annotated flow diagrams do not contain references to error messages, abnormal termination conditions, or most control block field
labels. This avoids complexity and makes the general logic of CP and
its related tasks more understandable to the user. With "understandability" as the key, obtuse and complex logic that is used
for obscure and seldom used functions is not described. Also the flow
diagram does not indicate nor describe every entry point encountered in
a function. Nor do the diagrams illustrate the innumerable times that
commonly used modules are utilized. DftKFRE and DftKCVT, the obtaining
and returning of free storage and the number base conversion modules are
such examples. Annotated flow diagrams are arranged by function and
subfunction. Titles for these functions and subfunctions also precede
annotated flow text and labels. The text in the charts is prefixed by
underscored and capitalized entry points and labels. Entry points are
indicated by seven or eight characters; the first three characters are
DMK. Labels are indicated by prefixing with a comma and the
six-character module identification.
The annotated flow diagrams in this section do not reflect V!/370 use
of the MSS. If there is an MSS attached to the VM/370 system, consult
Appendix B in this volume for flow diagrams of those functions that
utilize the MSS (such as logging on a virtual machine that has a mimidisk defined on an MSS 3330V voluae}0
Note: Annotated flow diagrams are not to be construed as trace material. The dynamics of CP operations preclude the use of the annotated flow
diagrams, as they are shown in this manual, as traces of CP functions. VM/370 CP Interruption Processing SVC INTERRUPTIONS - PROBLEM STATE DMKSVCIN --Entry for SVC problem mode
replaced. DMKCFMBK interruptions from problem or supervisor states. For
and ADSTOP (SVC X 'B3'), the overlaid instruction is ---console function mode is entered. DMKSVCIN state SVC 76 (X'4C') check for valid parameter passing. Determine the operating SCP used in the virtual machine by examining passed parameters in RO and R1. For invalid parameter passing, error recording is not performed. DMKIOEVR is reflected to the user. CP Method of operation and Program Organization 1-183
DMKIOFVR -- parameter reflection, record the error. DMKSVC, REFSVCB ---aEFSVCB--Is-ca11ed if TRACE SVC was in effect or if the virtual
machine's page zero is not in real storage. Obtains the system lock
before continuing. If the system lock is not immediately available, REFSVCB defers the interrupt and exits to DMKDSPRU. DMKTRCSV module is called if TRACE SVC was invoked. DMKPRGRF is not active, flag user as being in instruction wait
state and reflect the SVC back to the user. DMKSVC ---rf-the virtual machine's page zero is in real storage. generate and
store an old SVC PSi. Fetch the new SVC PSi. If there is no PSi state
change, store user's new PSi in RUNPSi, restore registers and
dispatch via LPSi. DMKSVC, REFSVCA there-Is a PSi state change, obtain the system lock before
continuing. If the system lock is not immediately available, defer
the interrupt and exit to DMKDSPRU. DMKDSPB ---Check the altered PSi. SVC INTERRUPTIONS - SUPERVISOR STATE Entry is for a system failure and is a SVC 0 or SVC 4 abend
condition. DMKDMPDK ---perform partial or full real storage dump. DMKCKPT ---Checkpoint the system. DMKCPINT ---perform an automatic IPL if indicated. DMKSVC, SVCLINK 8 provides linkage to a called routine in R15. DMKPTRUL routine is not resident, page it in and return control to
the caller by loading the SAVERTN into the old PSi and then load the
old PSi. The caller's addressabi1ity, SAVEAREA address and return
address are maintained in a new SAVEAREA. QMKSVC, Entry via SVC 12 return control from the called routine to the
calling routine and restores addressabi1ity via R12 and R13. DMKPTRUL module, unlock page to return it to DISD. Entry via SVC 16 to release the current SAVEAREA used by SVC 8 and Return to caller. DMKSVC, SVCGET via-SVC 20 to obtain a new SAVEAREA. Return to caller. Entry via SVC 24 to switch control to the main processor. EXTERNAL AND CLOCK INTERRUPTION REFLECTION DMKPSAEX via the interruption key on system console, adjust accounting
to charge for supervisor overhead. If problem Bode, attention
interruption, update the virtual machine PSi from the external old PSi. 1-184 IBM VM/370 System Logic and Problem Deteraination--Voluae 1
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