SYSTEM SUPPORT MODULES The system support modules provide CP with several co.mon functions for
data conversion and control block scanning and verification. ftost of
the routines are linked to via the BALR option of the CALL .aero, and
aake use use of the BALRSAVE and TEMPSAVE workareas in DftKPSA. Two exceptions are the virtual and real I/O control block scan routines DMKSCNVU and DMKSCNRU. These routines do not alter the contents of the BALRSAVE area, and hence may be called by another low-level BALR
routine. CONTROL REGISTER USAGE Every IBM System/370 processor provides the program with 16 logical
control registers (logical registers since the number that are active
depends on the features installed in the machine at anyone tiae) that
are addressable for loading and storing from basic control (BC) aode. VM/370 provides only a single control register, control register zero,
for normal virtual machines, and for processing systems that do not
require the full set of registers (for exaaple, CMS, DOS, or other
operating systems for System/360). Any user whose virtual machine operating system requires the use of
control registers other than control register zero, can request the full
set of 16 registers by specifying the ECBODE option in the Vft/37 0 directory entry for his virtual aachine. A virtual machine, which utilizes any Systea/370 features that use
the control registers, requires the ECftODE option. Soae of these
features are expanded timer support of the Systea/370 CPU tiaer, clock
comparator, etc., the virtual relocate mode and its instructions, RRB,
LRA, PTLB, virtual monitor calls, virtual Program Event Recording (PER), etc. RESTRICTIONS IND CONVENTIONS FOR PAGEABLE CP nODULES Pageable CP modules must observe the following restrictions and
conventions when they are designed and coded: • The module must be entered by the standard SVC Bodules entered by BALR or GOTO cannot be pageable.
return to its caller by SVC also.
8 CALL linkage. The module aust • The module cannot contain any A- or V-type address constants that
point to locations within itself or within other pageable modules, and it cannot contain any CCWs that contain data addresses within
themselves. The only exceptions are address constant literals
generated as the result of calls to other modules (because these
addresses are dynaaically relocated at execution time, they aust be
resolved by the loader to the loaded address of the called aodule)
and a pageable module that locks itself into storage. In practice,
this restriction means that data or instructions within the page able
routine must be referenced via base/displacement addressing, and the
address in register 15 for a CALL may not be generated by a LOAD ADDRESS instruction. • The pageable aodule aust be no more than 4096 bytes in length. CP Introduction 1-79

If the three above design and coding restrictions are adhered to, the CP module can be added to the existing pageable nucleus modules by
utilizing the service routine, V!FLOAD, which is described in "V!/370 Maintenance Procedures" of the !!l37Q Loqi£. Additional information can be found in the V!LJ1Q !ag !!§ig!nt !1ggul!§ DMKBSC DMKGRF DMKPRG DMKSSS DMKCCH DMKGRT D!KPRV D!KSTK DMKCCW DMKHVC DMKPSA DMKSVC DMKCFI1 DMKIOE DMKPTR D!KT!R DMKCNS DMKIOS DMKQCN D!KTRK DMKCVT DMKLOC D!KRGA D!KUNT D!KDAS D!KLOK DMKRGB D!KVAT DMKDGD D!KMCH DMKRNH DMKVCN DMKDMP D!KMCT DMKRPA DMKVIO DMKDSB DMKllSW DMKRS:P DiiKV5A DMKDSP DMKOPR D!KSCH D8KVSI DMKEXT DMKPAG DMKSCN D!KVSP D!KFRE D!KPGT 1!n£g!§ble f§.9!able !1 odul!!! DMKACO DMKCPB DMKDIB DMKNE! D8KTRC DMKALG DMKCPI D!KDRD D!KNES D!KTRD DMKAPI D!KCPS DMKEIG D!KHET D!KTR! DMKATS D!KCPU DMKER! D!KHLD DMKUDR D!KBLD D!KCPV D!KGIO D!KRLE D8KUDU D!KCDB D!KCQG D!KHVD D!KPGS D!KUSO D!KCDI1 DMKCQH D!KIOC D!KRSE D!KVCA D!KCDS D!KCQP D!KIOF D!KSAV D!KVCH D8KCFC DMKCQR D8KIOG D!KSEP D!KVDA D!KCFD D!KCQY D8KIS! D!KSEV D!KVDC D!KCFG D8KCSB D!KJRL D!KSIX D!KVDD D!KCFH D!KCSO DMKLHK D!KSHC D!KVDE D!KCFO D!KCSP DMKLOG D!KSPL D8KVDR D!KCFP DMKCSQ DMKLOH D!KTAP D!KVDS D!KCFS DMKCST DMK!CC D!KTCS D!KVER D!KCFT DMKCSU D!K!ID D!KTDK D!KV!C D!KCKP DMKCSV DMKMHI D!KTHI D!KVMI D!KCKS DMKDEF DMKMOH D!KTRA D!KWR! D!KCLK D!KDIA DMK!SG Figure 16. Executable Modules DATA AREA MODULES In addition to the executable resident and pageable modules (see Figure
16), there are certain modules that only contain data areas and do not
contain executable code. These modules are:
Resident
Module iiiCPE DMKGRW D!KBIO DMKSYS DMKTBL Contents Defines-the end of the CP nucleus
CCW's and data for 3218 model 2A I/O device blocks System constants Terminal translate table 1-80 IBM VM/370 System Logic and Problem Deteraination--Volume 1