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SPECIFICATION





                                STOPCD

                     LIST OF MONITOR ERROR STOPS










                    Date:     July, 1975
                    File:     STOPCD.RNO
                    Edition:  3










This document reflects the 6.02 release of the monitor.

The information in this document is subject to change  without  notice
and  should  not  be  construed  as  a commitment by Digital Equipment
Corporation.  Digital Equipment Corporation assumes no  responsibility
for any errors that may appear in this manual.

The software described in this document is furnished to the  purchaser
under  a license for use on a single computer system and can be copied
(with inclusion of DIGITAL's copyright notice) only for  use  in  such
system, except as may otherwise be provided in writing by DIGITAL.

Digital Equipment Corporation assumes no responsibility for the use or
reliability  of  its  software  on  equipment  that is not supplied by
DIGITAL.



Copyright  C  1971, 1972,  1973,  1974,  1975,  by  Digital  Equipment
Corporation, Maynard, Massachusetts
                                                                Page 2


1.0  INTRODUCTION

This document describes the different types  of  error  stops  in  the
monitor  and  then lists all the error stops that can occur.  When the
monitor detects an internal error it executes the STOPCD  macro  which
produces a message of the form:

          ?CPUn MONITOR ERROR.  STOPCODE NAME xxx

where n is the number of the CPU that executed the  STOPCD  macro  and
xxx  is a mnemonic in the STOPCD macro.  These mnemonics are listed in
Section 2.0 of this document.  Also listed are the name of the monitor
module  containing  the  STOPCD,  the  type  of  STOPCD,  and  a brief
explanation.

There are four types of STOPCD's:

     1.  DEBUG -   If  a  priority  interrupt  is  in  progress,   the
         condition  is  not  immediately  harmful to any job or to the
         system.  The monitor transmits the following message  to  the
         CTY:

              ?CPUn MONITOR ERROR.  STOPCODE NAME xxx
              CONTINUING SYSTEM

         and continues.  No immediate operator action is required.

         If no priority interrupt is in progress, a DEBUG STOPCD  acts
         and counts as a JOB STOPCD.

     2.  JOB -  If no priority interrupt is in progress, the condition
         jeopardizes  the  integrity  of the current job.  The monitor
         transmits the following message to the CTY:

              ?CPUn MONITOR ERROR.  STOPCODE NAME xxx
              ?ABORTING JOB

         and another message to the user's terminal:

              ?MONITOR ERROR;  UUO AT xxxxxxxx

         where xxxxxxxx is one of the following:

              USER LOC n
              EXEC LOC n;  EXEC CALLED FROM EXEC LOC m
              EXEC LOC n;  EXEC CALLED FROM USER LOC m

         The monitor then aborts the current job  and  continues.   No
         immediate operator action is required.

         If a priority interrupt is in progress,  a  JOB  STOPCD  acts
         like a STOP STOPCD.

     3.  STOP - The condition jeopardizes the integrity of the  system
         as  a  whole.  The monitor transmits the following message to
         the CTY:

              ?CPUn MONITOR ERROR.  STOPCODE NAME xxx
              RELOAD MONITOR

         All jobs are aborted and the system  initiates  an  automatic
                                                                Page 3


         reload of the monitor.

     4.  HALT - The condition is so serious that the entire system  is
         affected  and  the  monitor cannot be reloaded automatically.
         The system halts requiring that the operator manually perform
         the  entire  CRASH  procedure  as  described  in the Software
         Notebooks in the Operator's Procedure entitled CRASH,  Saving
         a  Crashed  Monitor  and  Restarting,  or in Chapter 5 of the
         Operator's Guide.



     In addition, if the monitor  can  determine  the  information,  a
     supplementary message:

         JOB n ON TTYxxx RUNNING xxxxxx
         UUO IS xxxxxxxxxxxx AT USER PC xxxxxx
         FILE dev:file.ext[n,m]

     is transmitted to the CTY after ?CPUn MONITOR ERROR in  order  to
     help the operator find the user causing the problem.



1.1  FINDING THE STOPCD'S IN THE CODE

Sometimes STOPCD's come up which are not documented.  This may be  the
result  of  patches  specific to an installation or patches made after
the release of the monitor.

If a STOPCD message comes up which can not be found  in  this  manual,
the  following  procedure  may  be  used to find the place in the code
where the STOPCD occurred.

First, consult the listing of the  monitor's  global  symbols  (GLOB).
The STOPCD's are listed as:

S..XXX     MODNAM   where XXX is  the  mnemonic  for  the  STOPCD  and
                    MODNAM  is the name of the module where the STOPCD
                    is coded.

By checking the CREF listing for the given module, the programmer  can
determine  the  line  number  where  the  STOPCD  can  be  found.  The
commentary that can be found in the code is sometimes  sufficient  for
determining how an error occurred.



1.2  HOW TO SET THE MONITOR TO RELOAD ON DEBUG AND JOB STOPCD'S.

As an added aid to debugging it is possible to cause a reload  on  all
STOPCD's.

There are two ways in which the system programmer can set the  monitor
to  reload  on  either the DEBUG or the JOB STOPCD's.  Both techniques
involve the setting of bits for the symbol DEBUGF or DEFDEB.  This can
be  done  by  changing  the contents of DEBUGF with FILDDT or EDDT, or
defining DEFDEB with MONGEN.  The bit values are:

          bit 0 = 1  This allows system debugging if EDDT is available
                     on the system.  If bit 0 = 0, a reload will occur
                                                                Page 4


                     on all STOP STOPCD's, if the system has  been  up
                     at least 5 minutes.

          bit 1 = 1  This causes a reload on all DEBUG STOPCD's.

          bit 2 = 1  This causes a reload on all JOB STOPCD's.

          bit 3 = 1  This disables auto reload.

          bit 4 = 1  This stops the system if CPU1 halts.


The following command sequence should be used to set the bits  through
FILDDT:

     .R FILDDT

     FILE:  SYSTEM/S                ; this loads the symbol table

     FILE:  /M/P                    ; enables the user to poke 
                                    ; locations
                                    ; in the running monitor.

     DEBUGF/300000,,0               ; this turns on both bits 1 and 2
                                    ; so there will be a reload on all
                                    ; STOPCD's
     ^Z                             ; EXIT

The same thing may be accomplished at MONGEN time.  When the  hardware
configuration dialogue asks for:

          OCTAL "SYMBOL, VALUE"

the programmer should enter:  DEFDEB,  300000000000.

If FILDDT was used to effect this change on the running  monitor,  any
crashes  wipe out the change.  However, if MONGEN was used, the change
is still in effect when the monitor is reloaded.  It is also  possible
to  patch a copy of the monitor on disk with DDT or FILDDT to make the
change effective after reloads.
                                                                Page 5


2.0  STOPCODES

NAME    ROUTINE    TYPE                     DESCRIPTION


28B     XTCSER     DEBUG      The  DA28  command  register   contained
                              erroneous  status  bits  during  an  I/O
                              operation.

4IF     FSXKON     DEBUG      "RP04 INVALID FUNCTION".  FILIO tried to
                              do an RP04 only function on an RS04 like
                              ECC error recovery or an unload.

5WE     D85INT     DEBUG      "DC75  WRONG  PDP11  CODE".   The  PDP11
                              designated as a DC75 was not running the
                              proper code.

6MS     D76INT     DEBUG      "DC76 MESSAGE IS SHORT".  A portion of a
                              message  was  lost  between the DC76 and
                              the -10.

6PP     D76INT     STOP       "DC76 PUTTER  PROBLEM".   There  was  an
                              interrupt  level  call to putter while a
                              non-interrupt call was in progress.

6QF     D76INT     DEBUG      "DC76  QUEUE  FULL".    The   queue   of
                              messages  to  the  DC76  was  full.  The
                              queue was designed to be big  enough  to
                              hold the worst case messages.

AAD     FILFND     DEBUG      "ACCESS  TABLE  ALREADY  DORMANT".    An
                              attempt  was  made  to  unlink an access
                              table from an NMB ring, but  the  access
                              table was already dormant.

AAO     KISER      JOB        "ACCESS ALLOWED OFF".  When the  monitor
        KLSER                 was remapping IOWD's from  user  virtual
                              addresses  to physical addresses, a page
                              map entry fetched from the  user's  page
                              map  had  the  access  allowed  bit  off
                              (virtual memory monitor only).

AES     FILFND     JOB        "ABNORMAL END OF SEARCH  LIST".   FILFND
                              got  to  the end of the search list when
                              it did not expect to be there.

AHB     FILIO      DEBUG      "ALREADY  HAVE  BUFFER".   The   monitor
                              attempted  to  get a monitor buffer when
                              it already had one.

AHS     ONCMOD     HALT       "ALREADY HAVE  STRUCTURE".   The  tables
                              which  drive  ONCMOD's  'DESTROY' option
                              duplicated a structure name.

AOC     FILFND     DEBUG      "ALREADY OWN CB".  A job wanted  the  CB
                              resource but already had it.

APE     KISER      JOB        "ABSOLUTE  PAGE EXCEEDED".  MAPIO  found
        KLSER                 an  IOWD  which  would  have  caused  an
                              address  check.   All  IOWD's  have been
                              checked prior to calling MAPIO.
                                                                Page 6


APF     VMSER      DEBUG      "ALLOCATED PAGE FREE".  While the  pages
                              allocated   to   a  segment  were  being
                              scanned, a page on the  free  core  list
                              was encountered.

AR1     ONCMOD     DEBUG      "ASKDEC RETURNED CPOPJ1".  ASKDEC gave a
                              skip return when one was not expected.

ARF     KISER      STOP       "ATTEMPT TO RETURN FREE PAGE".   A  page
        KLSER                 that was going to  be  returned  to  the
                              free core list was already free.

BAC     CORE1      JOB        "BIT ALREADY  CLEAR".   An  attempt  was
                              made  to  zero  bits which were not one.
                              This is  the  SETZRS  routine  which  is
                              called from many modules.

BAD     FILFND     JOB        "BLOCK ALREADY DORMANT".  An attempt was
                              made  to  put  an already dormant access
                              table in the free core list.

BAO     FILIO      DEBUG      "BIT ALREADY ONE".  The monitor tried to
                              allocate   a  block  which  was  already
                              allocated.

BAZ     FILIO      DEBUG      "BIT   ALREADY   ZERO".    The   monitor
                              attempted  to  return  blocks which were
                              already  free.   This  happens  when   a
                              damaged file is deleted.

BFO     TAPUUO     DEBUG      "BETTER FIND ONE".  When an attempt  was
                              made  to  generate the transfer list for
                              read backwards, the end of the  original
                              transfer list could not be found.

BFU     NETSER     DEBUG      "BUSY FOULED UP".  More than one  buffer
                              got allocated to the DC75 or DAS85.

BMR     FILUUO     JOB        "BLOCK MISSING FROM RIB".   A  block  in
                              the file was not pointed to by the RIB.

BNF     COMMON     HALT       "BOOTS NOT FOUND".  BOOTS could  not  be
                              found on disk.

BNR     FILUUO     JOB        "BLOCK NOT IN RIB".  A pointer was  lost
                              from the RIB.

BNT     FILFND     DEBUG      "BLOCK NOT THERE".  A core  block  (A.T.
                              or  UFB)  which was known to exist could
                              not be found.

BNZ     CORE1      DEBUG      "BIT  NOT  ZERO".   A  call  to   CSETOS
                              attempted to set a bit which was already
                              one.

BPT     FILFND     JOB        "BAD SEARCH  LIST  POINTER".   A  search
                              list could not be built.

BRC     COMCON     DEBUG      "BAD RETURN FROM CMPBIT".  When the flag
                              bits  for the directory entry were being
                              computed, a nonexistent page was found.
                                                                Page 7


BSN     SEGCON     STOP       "BAD SEGMENT NUMBER".  There was a  high
                              segment number discrepancy.

BSY     XTCSER     DEBUG      The DA28 interrupted with the busy  flag
                              set.

BTL     SCNSER     STOP       "BACKWARD TTY LINK".  The TTY buffer was
                              linked improperly causing the routine to
                              write   over   a   previously   received
                              character.

BWA     FILIO      JOB        "BLOCK WENT AWAY".   A  block  that  was
                              allocated was not there anymore.

C0P     COMMON     DEBUG      "CPU0 PARITY".   On  CPU0  there  was  a
                              parity   error   with  no  parity  error
                              recovery code, an I/O page failure, or a
                              timer time-out.

C1N     CP1SER     DEBUG      "CPU1  NXM".   Nonexistent  memory   was
                              encountered on CPU1.

C1P     COMMON     DEBUG      "CPU1 PARITY".   On  CPU1  there  was  a
                              parity   error   with  no  parity  error
                              recovery code, an I/O page failure, or a
                              timer time-out.

CAO     FILUUO     DEBUG      "CLUSTER  ADDRESS   ODD".    A   cluster
                              address could not be converted to a disk
                              block number.

CAS     REFSTR     HALT       "COULDN'T    ALLOCATE    SPACE".     The
                              refresher filled the disk.

CDD     MSGSER     JOB        "CAN'T DISCONNECT DEVICE".  The  release
                              call   on   MPX  called  disconnect  and
                              disconnect failed with an illegal format
                              or the device not connected.

CFP     CLOCK1     JOB        "CAN'T FIND PDB".  JBTPDB(J)=0 at  SETR2
                              in a monitor which does not swap PDB's.

CGS     ONCMOD     HALT       "CAN NOT GET STR".  The  DESTROY  option
                              could not create a structure data block.

CIF     FHXKON     DEBUG      "RC10 IS NOT FANCY".  An  RP04  function
                              was  attempted  on  an  RC10  controlled
                              device.

CIO     REFSTR     DEBUG      "CFP IS ODD".  The refresher noticed the
                              number  of  blocks  per  cluster did not
                              divide into the  number  of  blocks  per
                              supercluster.

CL0     SCNSER     STOP       "CHUNK LINK TO 0".  The TTY chunks  were
                              messed up.

CME     FILFND     DEBUG      "CFP MODULO ERROR".  CFP did  not  start
                              at an even supercluster boundary.
                                                                Page 8


CMS     VMSER      DEBUG      "CORE1 MUST SKIP".  CORE1 gave a nonskip
                              return when asked for core in use.

CMU     SEGCON     STOP       "CORE MESSED UP".  CHKTAL found that the
                              monitor's  core  usage  tables  did  not
                              check with each other.

CNA     SCHED1     STOP       "CORE   NOT   AVAILABLE".    The    core
                              allocation  routine gave an error return
                              while attempting to allocate core for  a
                              swap-in, after it had been verified that
                              enough core was available.

CNE     FILUUO     DEBUG      "CLUSTER NOT EVEN".  When an attempt was
                              made  to  allocate  initial blocks for a
                              file, the block which  was  computed  as
                              the  start  of  a  supercluster  did not
                              start at an even supercluster address.

CRE     TAPSER     DEBUG      "CANNOT  RECOVER  ERROR".    The   error
                              recovery  procedure  was  called with an
                              I/O   request   block   already   marked
                              nonrecoverable.

CRP     CORE1      JOB        "CANNOT RETURN PUSH DOWN LIST".   GIVEPL
                              was  called and the push down list would
                              not fit back into the job data area.

CRW     KILOCK     STOP       "CA RESOURCE WRONG".  The CA request was
                              not negative.  The interlock on the LOCK
                              call was not available, but no  one  was
                              doing a LOCK call.

CSA     COMCON     DEBUG      "CANNOT SET ACCESS ALLOWED".  During the
                              save  of an EXE file a page was paged in
                              but had its access allowed bit off.   An
                              attempt  to  turn  that  bit  on  failed
                              (virtual memory monitor only).

CSE     FILIO      STOP       "CHECKSUM ERROR".  The word  pointed  to
                              for  checksumming  was not in the user's
                              address space.

CWN     NETSER     DEBUG      "CORE ALLOCATION WENT NEGATIVE".  NETSER
                              attempted  to  give  back more free core
                              than it had.

DBZ     FILIO      DEBUG      "DEPLPC BIT ZERO".  The  last  group  of
                              pointers  for  a  file  was not the last
                              group in the RIB.

DCR     FILUUO     DEBUG      "DELRIB CPOPJ  RETURN".   DELRIB,  which
                              should  always  give  a skip return, did
                              not skip.

DDS     FILUUO     DEBUG      "DELRIB  DIDN'T  SKIP".   DELRIB,  which
                              should  always  give  a skip return, did
                              not skip.
                                                                Page 9


DER     FILUUO     DEBUG      "DELRIB RETURN  ERROR".   DELRIB,  which
                              should  always  give  a skip return, did
                              not skip.

DFU     NETSER     DEBUG      "DEVICE  UNRECOGNIZED".   UUOCON  called
                              the   network  service  routine  with  a
                              device not on the network.

DHA     FILIO      DEBUG      "DON'T HAVE AU".  The monitor  attempted
                              to  give  up the AU resource when it did
                              not have it.

DHB     FILIO      DEBUG      "DON'T HAVE BUFFER".  The buffer  return
                              routine had no buffer to return.

DHD     FILIO      DEBUG      "DON'T HAVE DA".  The monitor  attempted
                              to  give  up the DA resource when it did
                              not have it.

DNF     FILUUO     DEBUG      "DDB NOT FOUND".   No  predecessor  disk
                              device  data  block  was  found  when an
                              attempt was made to return a DDB.

DNR     FILUUO     DEBUG      "DELRIB NONSKIP RETURN".  DELRIB,  which
                              should  always  give  a skip return, did
                              not skip.

DNS     FILUUO     DEBUG      "DELRIB NONSKIP RETURN".  DELRIB,  which
                              should  always  give  a skip return, did
                              not skip.

DPL     COMCON     DEBUG      "DIRECTORY PAGE LOST".   The  page  that
                              had to be written out (not paged out) to
                              make room to create the  directory  page
                              could  not  be  brought back in (virtual
                              memory monitor only).

DPN     COMCON     DEBUG      "DIRECTORY   PAGE   NONEXISTENT".    The
                              directory  page  for  an  EXE  file  was
                              supposed to be destroyed, but  it  could
                              not be (virtual memory monitor only).

DPO     SEGCON     DEBUG      "DIRECTORY   PAGE   OVERLAP".    On    a
                              nonvirtual  memory  system another entry
                              was being fetched from the directory and
                              the   end   of  the  page  was  reached.
                              However, there is a limit of one page on
                              a nonvirtual memory system.

EPO     ERRCON     DEBUG      "EXEC  PDL  OVERFLOW".   The   monitor's
                              extended pushdown list overflowed.

ERB     REFSTR     DEBUG      "ERROR   READING   BAT   BLOCK".     The
                              refresher could not read the BAT block.

ERD     ONCMOD     DEBUG      "ERROR REFRESHING DISK".  REFSTR had  an
                              error refreshing a specific structure.

ERF     TAPSER     STOP       "ERROR RECOVERY FAILURE".  During  error
                              recovery  an  IORB  (I/O  request block)
                              other  than  this   controller's   error
                                                               Page 10


                              recovery IORB was posted complete to the
                              error recovery procedure.

ERH     REFSTR     DEBUG      "ERROR READING HOME.SYS".  The refresher
                              could not read HOME.SYS.

ERM     ONCMOD     DEBUG      "ERROR READING MFD".  An error  occurred
                              in   trying   to  read  the  MFD  during
                              ONCE-only.

ERP     REFSTR     HALT       "EXTRA RETRIEVAL POINTER".  The HOME.SYS
                              RIB  filled  up while the disk was being
                              refreshed.

ERS     ONCMOD     DEBUG      "ERROR READING SAT".  An error  occurred
                              while   reading  the  SAT  table  during
                              ONCE-only.

ESS     FILFND     JOB        "EMPTY SYSTEM SEARCH LIST".

EUE     ERRCON     DEBUG      "EXEC UUO ERROR".  The monitor  executed
                              an illegal UUO (call).

EWB     REFSTR     DEBUG      "ERROR WRITING  BLOCK".   The  refresher
                              had an error writing a block.

EWH     REFSTR     DEBUG      "ERROR  WRITING   HOME   BLOCKS".    The
                              refresher could not write home blocks.

EWR     ONCMOD     DEBUG      "ERROR WHILE REFRESHING".  The refresher
                              had  an  error  while refreshing all the
                              disks in the system.

FAD     FILUUO     DEBUG      "FILE ALREADY DORMANT".  An access table
                              was  found  to be dormant during a CLOSE
                              call.

FDP     FILIO      DEBUG      "FIXED-HEAD   DEVICE   POSITIONED".    A
                              position  done  interrupt  was  received
                              from a  fixed  head  device.   This  may
                              indicate a hardware problem.

FFU     NETSER     STOP       "F FOULED UP".  An attempt was  made  to
                              put  a job to sleep, but the job did not
                              exist.

FIP     VMSER      DEBUG      "FREE PAGE IN USE".  When the free  core
                              list was being scanned, a page allocated
                              to a segment was encountered.

FLE     SCNSER     STOP       "FREE LIST EMPTY".  The number  of  free
                              TTY  chunks did not agree with the count
                              of the number of free TTY chunks.

FPF     KILOCK     STOP       "PAGE ON FREE LIST IS NOT FREE".  A page
                              on  the  free  core list was linked to a
                              page which was  not  on  the  free  core
                              list.

FPI     KISER      STOP       "FREE  PAGE  IN USE".  A page taken from
        KLSER                 the free list was not free.
                                                               Page 11


FPN     KILOCK     STOP       "FREE PAGE NOT FOUND".  When a page  was
                              being  moved,  a free page in PAGTAB was
                              not on the free core list.

FPZ     SCNSER     STOP       "FREE POINTER  ZERO".   An  attempt  was
                              made  to  place  a  character in the TTY
                              buffer when the count of the  number  of
                              free  chunks  was positive, but the free
                              list was empty.

HBE     REFSTR     DEBUG      "HOME BLOCK ERROR".  An  error  occurred
                              during  an  attempt  to  read  the  home
                              blocks   while   refreshing    a    file
                              structure.

HDS     XTCSER     STOP       "HIBER DID NOT SKIP".   A  call  to  the
                              HIBER subroutine did not skip.

HIF     FILIO      DEBUG      "HOLE IN FILE".  Although the last block
                              in the file existed, some block prior to
                              the last was missing.

HWU     FILIO      JOB        "HARD WRONG UNIT".  The wrong unit on  a
                              disk  controller interrupted.  This is a
                              hardware problem.

IBI     CLOCK1     JOB        "INTERRUPT BLOCK ILLEGAL".  An interrupt
                              block  was  out of bounds in preparation
                              for an interrupt to a job.

IBZ     FILIO      JOB        "I/O TO BLOCK  ZERO".   An  attempt  was
                              made  to  read or write block zero.  The
                              only way block  0  can  be  read  is  by
                              reading   HOME.SYS[1,4]   or  using  the
                              SUSET.   call.   If  neither   condition
                              holds, there is a monitor error.

ICC     PSISER     HALT       "INVALID CONDITION CODE".  The condition
                              which  caused  this  interrupt  did  not
                              exist.

ICN     SEGCON     DEBUG      "INCORE COUNT NEGATIVE".  When the count
                              of the number of jobs in core which were
                              sharing a high segment was  decremented,
                              the count became negative.

ICW     KALOCK     DEBUG      "IN  CORE  COUNT  IS  WRONG".   A   high
                              segment  was  in  the way of a job to be
                              locked, and the low segments  associated
                              with  the  high  segment  could  not  be
                              found.

IDC     ONCMOD     HALT       "IMPOSSIBLE   DRUM   CONDITION".     The
                              nonexistent   "write   header   lockout"
                              switch for the RD10 was set.

IFI     TAPSER     STOP       "ILLEGAL FUNCTION AT  INTERRUPT  LEVEL".
                              An illegal function was found in an IORB
                              (I/O request block) while  at  interrupt
                              level.
                                                               Page 12


IFU     NETSER     DEBUG      "INTERRUPT FLAG  UNRECOGNIZED".   D85INT
                              called NETSER with an invalid interrupt.

IIP     FILIO      DEBUG      "IO IN PROGRESS".  An attempt  was  made
                              to  start  a  monitor read or write on a
                              DDB which was IO active.

IME     KISER      DEBUG      "ILL.  MEM-REF FROM EXEC".  An EXEC mode
        KLSER                 page fault took place.

INU     TAPSER     STOP       "INTERRUPT ON NONEXISTENT UNIT".  TAPSER
                              received   an  interrupt  to  service  a
                              nonexistent unit.

IPF     VMSER      DEBUG      "IN USE  PAGE  FREE".   When  the  pages
                              which  were  allocated to a segment were
                              being scanned, a page on the  free  core
                              list was encountered.

IPM     VMSER      DEBUG      "ILLEGAL   POINTER   IN   MEMTAB".    An
                              inconsistency   was   detected   in  the
                              swapping data base.

IPN     VMSER      DEBUG      "IPCF  PAGE  NONEXISTENT".   After  IPCF
                              pages  were  swapped  out, they were not
                              found in the swap list.

IRE     KISER      JOB        "IOWD  RELOCATION  ERROR".  Following  a
        KLSER                 job's  paging,  an  error  occurred   in
                              changing the IOWD to an absolute IOWD.

ISS     TX1KON     DEBUG      "IMPOSSIBLE STORED  STATUS".   The  TX01
                              generated  CU  status without device end
                              for a  unit  believed  to  be  off-line.
                              This should never happen.

IUN     FILUUO     DEBUG      "INVALID UNIT NUMBER".  MFD  RIB  for  a
                              file structure was on an invalid unit.

JAC     UUOCON     DEBUG      "JOB DATA AREA CLOBBERED".   JOBHCU  was
                              greater than 17.

JDJ     ONCMOD     DEBUG      "JFFO DIDN'T JUMP".  Logical unit number
                              could not be determined.

JIT     SYSINI     HALT       "JOB  IN  TRANSIT".   Lock was non-zero.

JNC     FILIO      DEBUG      "JOB NOT IN  CORE".   A  job  which  had
                              active  disk  I/O was not in core.  This
                              was detected  when  the  interrupt  took
                              place.

KAS     TAPSER     STOP       "KONTROLLER   ALREADY   STARTED".    The
                              controller  was  busy  when  TAPSER  was
                              ready to start I/O.

KDS     DPXKON     DEBUG      "KONEC2 DIDN'T  SKIP".   The  subroutine
                              KONEC2 should always give a skip return.

KID     SYSINI     HALT       "KONTROLLER IS DOWN".  A controller went
                              down during disk initialization.
                                                               Page 13


KN1     CP1SER     HALT       "KT10A NOT ON CPU1".  CPU1 does not have
                              dual     protection    and    relocation
                              registers.

KNF     XTCSER     STOP       "KONTROLLER NOT FREE".  A request by  an
                              external    processor   was   made   and
                              recognized by the DA28C  but  conflicted
                              with the current use of the controller.

KNS     TAPSER     STOP       "KONTROLLER NOT SELECTED".   An  attempt
                              was  made  to  start I/O on a controller
                              that was not selected.

KOL     TAPSER     STOP       "KONTROLLER OFF-LINE".   Start  I/O  was
                              called   on   a   controller   that  was
                              off-line.

LN1     ERRCON     STOP       "NO TTY LINE".  The controlling teletype
                              could not be found.

LNP     FILIO      DEBUG      "LAST  POINTER  NOT  A   POINTER".    An
                              allocation  was  done  and  a  RIB error
                              occurred.  When an attempt was  made  to
                              deallocate  the  space,  the RIB pointer
                              was not valid.

LNS     SCNSER     STOP       "LINE NOT SETUP".  RH(U)=0 on  the  call
                              to TSETBI.

LNT     ERRCON     STOP       "LDB (LINE) NOT THERE".  The controlling
                              teletype could not be found.

LPU     FILUUO     JOB        "LAST  POINTER  UNIT-CHANGE".   A   unit
                              change pointer was the last pointer in a
                              RIB, when a unit change  pointer  should
                              always be followed by a data pointer.

LTS     NETSER     DEBUG      "LINK  TO  SELF".   Buffers  pointed  to
                              themselves in a linked list.

MAU     CP1SER     DEBUG      "MASTER   ALREADY    UNLOCKED".     CPU0
                              attempted  to  give  up (unlock) the CPU
                              interlock, but it did not own  it  (have
                              it locked).

MCM     METCON     DEBUG      "MCDB MISSING".  After the metering of a
                              monitor data point, an attempt to remove
                              a Meter Channel Data Block failed.

MCN     FILFND     DEBUG      "MOUNT COUNT NEGATIVE".  The mount count
                              on a structure went negative.

MHB     FILIO      DEBUG      "MUST HAVE BUFFER".  An attempt was made
                              to read a RIB into a monitor buffer when
                              there was no monitor buffer for the job.

MIW     ONCE       STOP       "MEMORY INTERLEAVING WRONG".  There  was
                              a   memory   interleaving   error.   The
                              operator must correct the problem.
                                                               Page 14


MIZ     VMSER      DEBUG      "MEMTAB IS ZERO".  An inconsistency  was
                              detected in the swapping data base.

MMN     ERRCON     HALT       "MONITOR MEMORY NONEXISTENT".  A  memory
                              dropped  off-line, and one or more pages
                              of  the  monitor  were  in   nonexistent
                              memory.

MMP     ERRCON     HALT       "MONITOR MEMORY  PARITY".   The  monitor
                              referenced  an  instruction or important
                              data with bad parity.

MMR     KILOCK     STOP       "MOVING MONITOR PAGE NOT REQUIRED".  The
                              expected  number  of monitor pages to be
                              moved could not be moved, because  there
                              were no free pages to move them to.

MNM     SYSINI     STOP       "MONITOR IN  NONEXISTENT  MEMORY".   The
                              monitor  overlapped  a page of core that
                              was   previously   determined   to    be
                              nonexistent.

MPN     KILOCK     STOP       "MONITOR PAGE NOT FOUND".  A page of the
                              monitor to be moved was not found in the
                              exec.  page map.

MXM     MSGSER     JOB        "MPX: DDB MISSING".  The DDB  chain  got
                              messed up;  the pointer to an MPX DDB on
                              the DDB chain was not right.

NAP     FILUUO     JOB        "NOT  ADDRESS  POINTER".   A   retrieval
                              pointer  did  not  point to a valid disk
                              address.

NCA     CLOCK1     STOP       "NO CORE ASSIGNED".  An attempt was made
                              to  start  a  job  with  no  core memory
                              assigned.

NDA     FILFND     JOB        "NO DUMMY ACCESS TABLE".  The routine to
                              remove the dummy A.T.  (TAKOU) could not
                              find the block to delete.

NDC     ONCMOD     STOP       "NO  DF10C  CODE".   Monitor   was   not
                              assembled  for  DF10C  in  KI mode.  Set
                              switch inside cabinet door to KA mode.

NDJ     SCNSER     DEBUG      "NO DDB FOR JOB".  A job's TTY  DDB  did
                              not  exist.   All  jobs  (even  detached
                              jobs) must have a DDB.

NDP     CLOCK1     DEBUG      "NOT DDB  POINTER".   WSYNC  was  called
                              with a strange address in F.

NDS     CLOCK1     STOP       "NULL  JOB  DID  SAVGET".   The   MONSTR
                              routine  was  called  while the null job
                              was running.

NED     ONCE       HALT       "NO EXEC  DDT".   ONCE  determined  that
                              there were breakpoints set, but EDDT was
                              not loaded with this monitor.
                                                               Page 15


NER     FILUUO     DEBUG      "NO EXTENDED RIB".  The pointer  to  the
                              last  block  of  the file was not in the
                              RIB and there was no extended RIB.  This
                              happens  when  a  pointer  gets lost for
                              some reason.

NEV     UUOCON     STOP       "NO EVM".  The DDB did  not  have  exec.
                              virtual memory.

NFC     SCNSER     STOP       "NO FREE CORE".  All the TTY chunks were
                              used up.  This condition was checked for
                              earlier and space was available.

NFS     VMSER      DEBUG      "NO FIRST SLOT".   At  the  start  of  a
                              fragment, the first physical page of the
                              fragment could not be found in the  page
                              map.

NFU     SYSINI     DEBUG      "NO FIRST UNIT".  There was not a  first
                              unit in the system search list.

NHF     KALOCK     STOP       "NO HOLE FIT".  HOLSRT could not find  a
                              hole  for  this  job  even though KALOCK
                              just created one.

NIV     TAPUUO     STOP       "NULL INTERRUPT VECTOR ADDRESS".  An I/O
                              request  block was executed and returned
                              to TAPUUO with a zero interrupt vector.

NMB     FILIO      DEBUG      "NEED MONITOR BUFFER".  An  attempt  was
                              made  to  write  a RIB without a monitor
                              buffer to write it from.

NMC     ONCMOD     HALT       "NO MORE  CORE".   ONCE-only  filled  up
                              core.

NMU     REFSTR     DEBUG      "NO MORE UNITS".  The refresher wrote  a
                              wrong RIB.

NNF     FILUUO     DEBUG      "NMB NOT FOUND".  GETNMB could not  find
                              a  name  block.  Either DEVACC or ACCNMB
                              was wrong.

NNR     FILUUO     JOB        "NO NEXT RIB".  During a  CLOSE  monitor
                              call  the  last  block of the file could
                              not be found.   This  indicates  that  a
                              data pointer was lost.

NNU     ONCMOD     DEBUG      "NOT NEW UNIT".  The monitor expected to
                              find  a  new  unit pointer while reading
                              SAT.SYS.

NOT     SCNSER     DEBUG      "NO OPR TTY".  DEVOPR=0.

NPC     SCHED1     STOP       "NO PDB IN CORE".  When an  attempt  was
                              made  to  requeue  a  job  and reset its
                              quantum run time, no process data  block
                              was found for that job.

NPD     FILIO      DEBUG      "NO POINTERS IN DDB".  An  extended  RIB
                              was  needed  because the pointers in the
                                                               Page 16


                              DDB were exhausted, but  there  were  no
                              pointers in the DDB.

NPF     KILOCK     STOP       "NEXT   PAGE   FREE".     The    monitor
                              encountered  a free page while searching
                              a segment's pages for the target page.

NPJ     DATMAN     DEBUG      "NO PDB FOR JOB".  A call to FNPDBS  did
                              not find a PDB.

NPN     KASER      STOP       "NONEXISTENT  K/PAGE  NOT FREE".  A K or
        KISER                 page of  nonexistent  memory belonged to
        KLSER                 either the monitor or  some  job.   This
                              should   only  happen  if  the  operator
                              continues after a NXM halt.

NPP     KISER      STOP       "NO PI IN PROGRESS".  Channel 7 code was
        KLSER                 called from UUO level.  The  page  table
                              could be messed up if this were allowed.

NPU     ERRCON     STOP       "NULL PUSH-DOWN UNDERFLOW".  There  were
                              more  POP's  on  the  null pushdown list
                              than matching PUSH's.

NRB     TAPSER     STOP       "NO REQUEST BLOCK".   A  done  interrupt
                              occurred on a controller or unit, and no
                              request block was found corresponding to
                              the interrupt.

NRF     VMSER      DEBUG      "SWPLST NOT REALLY  FRAGMENTED".   There
                              was  a  pointer  to  a fragmented SWPLST
                              entry, but  the  entry  was  not  really
                              fragmented.

NRM     FILUUO     JOB        "NEXT  RIB  MISSING".   There  were  not
                              enough  pointers  in  the RIB to account
                              for the number of  blocks  written,  and
                              there were no more RIB's.

NRS     ONCMOD     DEBUG      "NO RIB IN  SAT".   SAT.SYS  had  a  RIB
                              error.

NSE     VMSER      DEBUG      "NO SWPLST ENTRY".  When an attempt  was
                              made  to  compute  the  unit  and  block
                              number represented by  a  SWPLST  entry,
                              the pointer to SWPLST pointed to a zero.

NSL     FILFND     JOB        "NO SUCH SEARCH LIST".  When an  attempt
                              was made to find the search list pointer
                              for the  current  job,  either  the  job
                              number  was  0, there was no PDB, or the
                              search list was null.

NSR     REFSTR     HALT       "NO SECOND RIB".  The refresher tried to
                              create a file with only one RIB.

NSS     REFSTR     DEBUG      "NO  SPACE  FOR  SAT".   The   refresher
                              filled up the disk.

NSU     FILIO      DEBUG      "NO SUCH  UNIT".   The  RIB  of  a  file
                              indicated a nonexistent unit.
                                                               Page 17


NUB     FILFND     JOB        "NO UFD BLOCK".  There was no UFD for  a
                              file even though the file existed.

NUE     FILUUO     JOB        "NO UFD ERROR".  There was no UFD for  a
                              file being written.

NUI     XTCSER     DEBUG      "NONEXISTENT  UNIT  INTERRUPT."  A  unit
                              which  was  not known interrupted.  This
                              occurs when the content of  the  feature
                              register is wrong during system loading.

NUP     FILUUO     DEBUG      "NO UNIT CHANGE POINTER".  The  RIB  did
                              not start with a unit change pointer.

NUS     VMSER      DEBUG      "NO UNIT FOR SWAPPING".   There  was  no
                              unit   in   the   active  swapping  list
                              corresponding to the unit  indicated  by
                              an entry in SWPLST.

NWD     FILIO      DEBUG      "NO WRITING DDB".  FILIO  thought  there
                              were  multiple writers and had to update
                              the DDB's, but  no  writing  DDB's  were
                              found.

NXU     FILIO      DEBUG      "NONEXISTENT  UNIT".   A   unit   change
                              pointer pointed to a unit which does not
                              exist in this structure.

O1F     VMSER      DEBUG      "ONLY ONE (1) FRAGMENT".  Swapping space
                              was  fragmented,  but there was only one
                              entry in the fragment table.

ONC     FILUUO     DEBUG      "ODD NUMBERED CLUSTER".  The  number  of
                              blocks  allocated  to  a file was not an
                              even multiple of the number of  clusters
                              allocated.

P2L     VMSER      STOP       "PAGE  TOO  LOW".   An  address  in  the
                              user's  page  map  was too low, i.e., in
                              the monitor.

PAO     COMCON     STOP       "PAGE ALREADY OUT".  After  a  page  was
                              paged  out  to create a directory for an
                              EXE file, the directory still could  not
                              be created.

PCN     IPCSER     DEBUG      "PACKET COUNT NEGATIVE".  The count  for
                              the   system's   unreceived  sends  went
                              negative.

PDA     FILIO      DEBUG      "POINTERS WITH DIFFERENT ADDRESSES".   A
                              pointer   within  the  RIB  and  monitor
                              buffer differed.

PEW     VMSER      DEBUG      "PAGTAB ENTRY WRONG".   When  the  pages
                              allocated   to   a  segment  were  being
                              scanned, a page on the  free  core  list
                              was encountered.

PEZ     KISER      STOP       "PAGPTR EQUALS ZERO".   The  pointer  to
        KLSER                 the free core list was found to be  zero
                                                               Page 18


                              when  an attempt was made to find a free
                              page.

PFA     KILOCK     STOP       "PAGE  FREE   ALREADY".    The   monitor
                              encountered  a free page while searching
                              a segment's pages for the target page.

PFC     VMSER      STOP       "PAGE ON  FREE  CORE  LIST".   When  the
                              pages  allocated to a segment were being
                              scanned, a page on the  free  core  list
                              was encountered.

PGL     COMCON     STOP       "PAGES GOT LOST".  No pages  were  found
                              that could be paged out to make room for
                              the directory of an  EXE  file  (virtual
                              memory monitor only).

PIE     ERRCON     STOP       "PRIORITY  INTERRUPT  ERROR".   A   jump
                              occurred  to  40  + 2n +..., n=1,2,...7.
                              This is caused by a device  interrupting
                              to the wrong location.

PIF     VMSER      DEBUG      "PAGE  IS   FREE".    When   the   pages
                              allocated   to   a  segment  were  being
                              scanned, a page on the  free  core  list
                              was encountered.

PIN     VMSER      DEBUG      "PAGE IN WORKING SET".  A page which was
                              verified  to  not  be in the working set
                              was in it.

PIP     KISER      DEBUG      "PI IN PROGRESS".  A trap took  place at
        KLSER                 PI-level,    usually    pushdown    list
                              overflow.

PIW     VMSER      DEBUG      "PAGE IS NOT IN WORKING  SET".   A  page
                              which  had  to be in the working set was
                              not.

PJ0     CLOCK1     DEBUG      "REQUEUE JOB 0".  An attempt was made to
                              requeue job 0 (the null job).

PLP     FILIO      DEBUG      "PAST LAST POINTER".  SCNPTR  could  not
                              find  a  block which should have been in
                              the file.

PMU     KISER      STOP       "PAGTAB MESSED UP".  The table used  for
        KLSER                 core allocation was not correct.

PNE     FILIO      DEBUG      "POINTERS   NOT   EQUAL".    After   the
                              pointers  in  the  RIB were updated from
                              the DDB, a discrepancy was found in  the
                              cluster number.

PNM     FILFND     DEBUG      "PHYSICAL   NAME    MISMATCH".     After
                              determining  that  a  name referred to a
                              disk unit, the physical name was lost.

PNP     KILOCK     STOP       "PAGE  NOT  PRESENT".   The  destination
                              could not be found in the free core list
                              or in the present segment.
                                                               Page 19


POP     CLOCK1     DEBUG      "PI ON PROGRESS".  An APR error happened
                              while  at  PI  level.  This was either a
                              NXM (any processor) or  a  PDL OV  (KA10
                              only).   The KI10 or KL10 will stop with
                              IME or PIP, as well as with this STOPCD.

POR     SEGCON     STOP       "PROCESS OUT OF RANGE".  An attempt  was
                              made  to  add  a  high  segment  to  the
                              address space of a nonexistent job.

PQE     FILIO      DEBUG      "POSITION QUEUE EMPTY".  A disk unit was
                              in  position  wait state, but there were
                              no files in its queue to be positioned.

PSF     KISER      STOP       "PAGE IN SEGMENT FREE".  When space  was
        KLSER                 being allocated for this job, a page  on
                              the  free core list was found within the
                              job.

PTH     KLSER      HALT       "PARITY TRAP HALT".  There  was  a  hard
                              exec.   mode  page fail trap as a result
                              of AR or ARX parity.

PTP     KLSER      HALT       "PAGE TABLE PARITY".  There was  a  hard
                              page  fail  trap  as  a result of a page
                              table parity error.

PTT     CORE1      JOB        "PAST TOP OF TABLE".  A call  to  SETZRS
                              attempted   to   zero   more  bits  than
                              existed.

RBQ     SCHED1     STOP       "REQUEUING TO BEGINNING OF  QUEUE".   An
                              attempt  was  made  to  requeue  to  the
                              beginning of a  queue  which  is  always
                              illegal in the 602 scheduler.

RCC     SCNSER     STOP       "RANGE CHECKED CHUNK".  A call to TTPUTC
                              or  TTGETC specified a character address
                              (in T2) which was not in the TTY  buffer
                              pool.    This  is  sometimes  caused  by
                              attempting TTY output without setting up
                              U to point to an LDB.

RDP     FSXKON     DEBUG      "RS04 DOES NOT POSITION".   FILIO  tried
                              to do positioning on an RS04.

RDS     SEGCON     STOP       "REMAP DID NOT SKIP".  Monitor was doing
                              a remap and an error occurred.

REH     ERRCON     HALT       "RECURSION IN ERROR HANDLER".  A  STOPCD
                              was  executed  while STOPCD recovery was
                              in progress.

RFU     TAPSER     STOP       "RECOVERY  FOULED  UP".   During   error
                              recovery   the   ERP   (error   recovery
                              procedure) state  word  had  an  invalid
                              state  number  at  the  completion of an
                              operation.

RIE     XTCSER     DEBUG      "REMOTE  INTERRUPT  ERROR".   An   error
                              occurred  during  an  interrupt  from  a
                                                               Page 20


                              remote processor.

RIF     DPXKON     DEBUG      "RP10 IS NOT FANCY".  An  RP04  function
                              was  attempted  on  an  RP10  controlled
                              device.

RJZ     SCHED1     STOP       "REQUEUE  JOB  ZERO".   A  job  with  an
                              invalid job number was being requeued.

RNA     TAPSER     STOP       "REQUEST NOT ACTIVE".  There was a  done
                              interrupt,   and   the   request   block
                              corresponding to it was not active.

ROS     SEGCON     JOB        "RAN OUT OF  SEGMENTS".   There  was  no
                              high  segment  number available to add a
                              high segment to a job's  address  space.
                              This  should  not  happen, because there
                              are always at least as many high segment
                              numbers   available  as  there  are  job
                              numbers available.

ROU     ONCMOD     HALT       "RAN OUT OF UNITS".  When an attempt was
                              made to get the address of the next data
                              block  in  the  structure,  the  pointer
                              indicated the end of the list.

RPM     ONCMOD     DEBUG      "RETRIEVAL POINTER MISMATCH".  The  unit
                              change  pointer  in file SAT.SYS did not
                              point to  the  next  unit  in  the  file
                              structure.

S2L     SWPSER     STOP       "SWAP  TOO  LOW".   A  swapping  request
                              would have clobbered part of the monitor
                              (nonvirtual memory monitor only).

SAC     ERRCON     DEBUG      "STRANGE  APR   CONDITION".    The   low
                              priority  APR  service routine could not
                              find  any  errors,   though   the   high
                              priority  APR  service  routine  said an
                              error took place.

SAU     CP1SER     DEBUG      "SLAVE ALREADY  UNLOCKED".   UNLOKS  was
                              called but the interlock was not set.

SBT     FILUUO     DEBUG      "SHOULD NOT BE TRUNCATING".  The highest
                              block number in the file was too small.

SBW     VMSER      DEBUG      "SWPLST BITS WRONG".  An entry in SWPLST
                              said  that  both I/O was in progress and
                              I/O was done.

SCB     XTCSER     DEBUG      "SPURIOUS CONI BITS".  A DA28C interrupt
                              occurred for no valid reason.

SCO     CP1SER     HALT       "SPLIT CYCLE ON".  CPU1 had:

                              1.  Address stop switch set, or

                              2.  Fast AC's turned off.
                                                               Page 21


SER     FILUUO     JOB        "SETDDO ERROR  RETURN".   There  was  no
                              room  to  build a DDB even though GET4WD
                              had just found room.

SFI     FILUUO     JOB        "STR  FREE-COUNT   INCONSISTENT".    The
                              structure  had  free  space but no units
                              within the  structure  had  free  space.
                              The sum of the parts exceeded the whole.

SFU     FILIO      DEBUG      "SWAPPER FOULED UP".  The swapper  tried
                              to do I/O with a nonswapping DDB.

SIN     VMSER      DEBUG      "SWPCNT IS NEGATIVE".  The count of  the
                              number  of outstanding swapping requests
                              went negative when an entry from  SWPLST
                              was being deleted.

SLF     VMSER      DEBUG      "SWPLST FULL".  An entry  could  not  be
                              made  in  the  list  because  the SWPLST
                              table was full.

SLM     FILUUO     DEBUG      "SEARCH LIST MISSING".  SETSRC could not
                              set  up  the  search list even though it
                              could when the monitor call started.

SLZ     VMSER      DEBUG      "SLECNT IS  ZERO".   The  subroutine  to
                              find  an entry in SWPLST was called when
                              there were no entries in SWPLST.

SMU     SCHED1     DEBUG      "SWPCNT MESSED UP".  The  count  of  the
                              number  of completed swapping operations
                              was positive, but no completed  swapping
                              request  could  be found (virtual memory
                              monitor only).

SNF     KILOCK     STOP       "SEGMENT NOT FOUND".  A page  which  was
                              not  on  the  free  core  list  was  not
                              contained  in  any   segment's   address
                              space.

SNI     SWPSER     DEBUG      "SWAPPING  NOT  IN  PROGRESS".    SPRCNT
                              (number   of  swaps  in  progress)  went
                              negative (virtual memory monitor only).

SOD     SCHED1     STOP       "SPACE ON DISK".  The call to CORGET  in
                              SWAPI  assigned space on the disk.  That
                              is not allowed on a swap-in.

SOR     ERRCON     STOP       "SEGMENT OUT  OF  RANGE".   The  segment
                              number  in  AC  J  was  larger  than the
                              maximum segment number in the system.

SPM     FILUUO     JOB        "SECOND POINTER MISSING".   The  pointer
                              to  the  second RIB was missing from the
                              first RIB.

SRE     ONCMOD     DEBUG      "SAT  READ  ERROR".   ONCE-only  had  an
                              error reading the SAT table.
                                                               Page 22


SRO     SWPSER     DEBUG      "SPACE RAN OUT".  VIRTAL  was  positive,
                              but no swapping unit had any room on it.

SSD     SWPSER     STOP       "SWAP SPACE DISAPPEARED".  The count  of
                              the  number  of  words of swapping space
                              free showed  more  space  than  the  SAT
                              table for swapping.

SSM     TX1KON     STOP       "STORED STATUS MISSING".  When the  DX10
                              should  have  stored extended status, it
                              did not.

SSO     KILOCK     STOP       "SEGMENT SWAPPED OUT".  A  high  segment
                              which  was  neither dormant nor idle had
                              no low segment in core sharing it.

SWJ     VMSER      DEBUG      "SWAPPED IN WRONG JOB".  The job  number
                              of the job just swapped in did not match
                              the job number in the UPMP.

SWN     SWPSER     DEBUG      "SQREQ WENT NEGATIVE".   SWPSER  got  to
                              SWPINT  when the swapper thought nothing
                              was happening  (virtual  memory  monitor
                              only).

TC0     XTCSER     DEBUG      Work entries which were queued when  the
                              DA28C was busy were not executed.

TC1     XTCSER     STOP       The LIPS protocol status was wrong  when
                              an I/O transfer started.

TC2     XTCSER     DEBUG      A remote  processor  interrupt  occurred
                              when  the control was not idle, i.e., in
                              use by software.

TC3     XTCSER     DEBUG      The accounting for  pseudo-active  tasks
                              in the control data block was wrong.

TC4     XTCSER     DEBUG      The accounting for  pseudo-active  tasks
                              in a unit control block was wrong.

TC5     XTCSER     DEBUG      The accounting for  pseudo-active  tasks
                              in a unit control block was wrong.

TC6     XTCSER     DEBUG      The accounting for  pseudo-active  tasks
                              in the control data block was wrong.

TC7     XTCSER     STOP       A job that was trying to grab the  DA28C
                              control obtained it, but the control was
                              not free according to the  control  data
                              block.

TCI     FILUUO     DEBUG      "TRUNCATION  CHECK   INCONSISTENT".    A
                              rename   which  was  causing  truncation
                              attempted to truncate  too  many  blocks
                              even though that was already checked.

TMP     FILIO      DEBUG      "TOO MANY POINTERS".   There  were  more
                              retrieval  pointers  than would fit in a
                              RIB.  There is  a  counter  (DEVRSU)  to
                              prevent this from happening.
                                                               Page 23


TMR     REFSTR     HALT       "TOO  MANY  RETRIEVAL  POINTERS".    The
                              SAT.SYS RIB filled up during a refresh.

TMU     ONCMOD     HALT       "TOO MANY UNITS".  After the  last  unit
                              was  retrieved,  additional  data blocks
                              were pointed to.

TOW     CP1SER     HALT       "TRAP OFFSET WRONG".  The CPU1 interrupt
                              vector was in the same place as the CPU0
                              interrupt vector.

UAS     TAPSER     STOP       "UNIT ALREADY STARTED".   The  unit  was
                              already  doing I/O when TAPSER was ready
                              to start I/O.

UDE     FILIO      DEBUG      "UNIT DOESN'T  EXIST".   A  unit  change
                              pointer  pointed  off  into  never-never
                              land.

UDM     FILUUO     JOB        "UFD DATA  MISSING".   The  core  tables
                              indicated  that  the UFD was longer than
                              it really was.

UFI     FILUUO     DEBUG      "UNIT FREE-COUNT INCONSISTENT".  No free
                              space  was  found  on a unit even though
                              the free-count was positive.

UIF     ONCMOD     HALT       "UNIT IN FILE  STRUCTURE".   The  tables
                              which drive ONCE-only's 'DESTROY' option
                              duplicated a unit.

UIL     ERRCON     STOP       "UUO AT INTERRUPT LEVEL".  An  interrupt
                              service   routine  executed  an  illegal
                              monitor call.

UIP     XTCSER     DEBUG      "NOT A UNIQUE INTERRUPT".  Two different
                              types  of  usage  were  defined  for the
                              DA28C control.

UNF     FILUUO     DEBUG      "UFB NOT  FOUND".   A  rename  was  done
                              across UFD's and the UFB was not found.

UNJ     COMMON     DEBUG      "UUO  FROM  NULL  JOB".   The  null  job
                              executed  a  monitor call other than the
                              doorbell monitor call.

UNL     VMSER      DEBUG      "UPMP NOT LAST".  The UPMP was  not  the
                              last page swapped out.

UNS     TAPSER     STOP       "UNIT NOT SELECTED".   A  unit  was  not
                              selected  when TAPSER was ready to start
                              I/O.

UPC     FILUUO     JOB        "UNIT CHANGE  POINTER  CLOBBERED".   The
                              pointer  to  a  unit  of  a RIB was lost
                              during RIB definition.

UPI     FILIO      DEBUG      "UNIT POINTER ILLEGAL".  An attempt  was
                              made  to  create  an  extended  RIB on a
                              nonexistent unit.
                                                               Page 24


UWS     VMSER      DEBUG      "UNIT WRONG STATE".  On a hung  swapping
                              device  the  UDB indicated an unexpected
                              state.

WAD     VMSER      DEBUG      "WSBTBL  AND  AABTBL  DISCREPANCY".   An
                              access  page  fault  occurred for a page
                              which should have had the access allowed
                              bit on in the page map.

XTH     SCHED1     DEBUG      "XJOB  TOO  HIGH".   The  count  of  the
                              number of jobs which must be swapped out
                              and back in to satisfy a core  expansion
                              request  was  positive, but no expanding
                              job could be found.

ZBC     REFSTR     DEBUG      "ZERO   BLOCKS   PER   CLUSTER".     The
                              refresher was called with HOMBPC=0.