ihen CMS can no longer continue, it abnormally terminates. To debug CMS, first determine the condition that caused the abend and then find
why the condition occurred. In order to find the cause of aCeS problem, you must be familiar with the structure and functions of CMS. Refer to "Part 3: Conversational Monitor System (CMS)" for functional
information. The following discussion on reading CMS dumps refers to
several eMS control blocks and fields in the centrol blocks. Refer to
the VML11Q gDQ 1Qgi£ for details on CMS control
blocks. Figure 12 shows the CMS control block relationships. You will
also need a current CMS nucleus load map in order to analyze the dump. REASON FOR THE ABEND
Determine the immediate reason for the abend and identify the failing module. The abend message DMSABN148T contains an abend code and failing
address. The VML11Q manual lists all the CMS abend
codes, identifies the module that caused the module to abend, and
describes the action that should be taken whenever eMS abnormally
terminates. You may have to examine several fields in the nucleus constant area (NUCON) of low storage. 1. Examine the program old PSi (PGMOPSW) at location Using the PSi and current CMS load map# determine the failing address.
2. Examine the SVC old PSi (SVCOPSi) at location X'20'. 3. Examine the external old PSi (EXTOPSi) at location X'18'. If the
virtual machine operator terminated CMS, this PSi points to the
instruction executing when the termination request was recognized.
4. For a machine check, examine the machine check old PSi (MCKOPSW) at
location X'30'. Refer to Figure 47 in "Appendix A: System/370 Information" for a description of the PSi. Part 1. Debugging with VM/370 69

DMSNUC USERSECT SUBSECT OPSECT DMSABW DMSFRT DMSERT DBGSECT (Debug work areal CVTSECT(Some fields are filled in
at IPl.) FVS DIOSECT SVCSECT PGMSECT IOSECT EXTSECT AFTSECT (Create when the file is
opened. There is room for 5 AFTs in DMSNUC, others are in free storage. ADTSECT (Space is allocated when DMSNUC is assembled, fields are filled in when ACCESS command is
issued. There is one ADT entry for
each of the 10 possible disks.)
DEVTAB
Terminal Buffers and Saveareas NUCON Figure 12. CMS Control Blocks COLLECT INFORMATION CMSCB DCB DECB I eM'AVE I B Examine several other fields in NUCON to analyze the status of the CftS system. As you proceed with the dump, you may return to NUCON to pick up
pointers to specific areas (such as pointers to file tables) or to
examine other status fields. The complete contents of NUCON and the
other CMS control blocks are described in the The following areas of NUCON may contain useful
debugging information.