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! d i g i t a l !   I N T E R O F F I C E  M E M O R A N D U M
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				       Date: 19-February-82
				       From: TSG/NCSS
				       Loc:  MR1-2/H22
				       Ext:  HOTLINE  5911
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Subj:	Debugging Hints for RSX20F
.subtitle Subj:	Debugging Hints for RSX20F
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The following is a general guide to debugging RSX20F problems. It is
not meant to provide a sure-fire way to analyze and correct all RSX20F
problems. Instead it is more of a directory of resources and information
gathering proceedures.
.hl 1 Attacking the Problem
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When you encounter a RSX20F problem:
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.le;Read the "RSX20F System Reference Manual" in the notebook set
particularly Chapters 9 and 10.  Appendix A contains a list of
RSX20F stop codes and their meaning.
.le;Write down exactly what seemed to be
happening on the system, what signals told you a problem existed,
and what attempts you made to recover from the problem.  This will
often help clarify your thinking and will provide the hotline with
necessary background information.  Also find out when the problem
was first noticed and if there is any way to reproduce the problem.
.le;Find out exactly what devices are involved,
in particular, what the hardware interface is and what it is connected
to.  Also check for any nonstandard device that has been hooked to
RSX20F, since these are often the cause of unusual problems.
.le;Get a copy of the console typeout at the time of the
crash along with any recent odd occurrences, and the CHK11 typeout
described in this SWSKIT.
.le;Use SYSERR (or SPEAR) to check for any entries generated by the problem or
that were generated around the time the problem occured.
.le;Use DDT11 to look at the running RSX20F.  DDT11.MEM in the
SWSKIT describes the /FESYMB switch to load the symbols to make
a front end specific DDT11 and the /FE:n to examine it.
.le;Use DDT11 and the command files provided to examine any
dumps that have been taken of the Console Front End.  Chapter 10
in the RSX20F System Reference manual is devoted to error debugging
and has a sample dump analysis and the data structures.  See page
10-41 for how to access device registers in the I/O page.
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.hl 1 Automatic Reloading
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There are two circumstances under which TOPS10 or TOPS20 will cause
a dump of RSX20F to be taken. The first is when TOPS10 or TOPS20 detects
that RSX20F is not incrementing the KEEP-ALIVE COUNTER. This can happen
when RSX20F loops or when RSX20F halts (either by executing the HALT
instruction or by depressing the HALT SWITCH on the front panel). A
dump taken under this condition will be missing a good deal of information
since the RSX20F crash routines were not executed. The second case is
when RSX20F detects an internal error and crashes. The last thing the
crash code does is to ring the KL's DOORBELL and request a reload. In
this case the state of RSX20F has been saved by the crash code and may
be extracted from the dump by using DDT11.
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Please note that when RSX20F crashes TOPS20 will always try to
dump and reload it. TOPS10, however, requires that a program called
DTELDR be running with the /DUMP and /AUTO switches in order to effect
an automatic reload.
.hl 1 Taking a Dump
The best dump is one produced when the PDP-11 detects an error and crashes.
However, RSX20F does not always cooperate and crash when you want it to.
Sometimes you must induce a reload so you can look at RSX20F's databases.
Producing a dump manually can be done in a number of ways:
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.le;By depressing and raising the halt switch.
.le;Use DNLOAD under TOPS20 or DTELDR under TOPS10. (Refer to the
appropriate documentation in the software notebooks.
.le;Use DDT11 to poke an illegal instruction into the running front
end's memory in a place you feel reasonably sure it will get executed
(i.e. in the DH11 interrupt routines...).  This will cause a stopcode
giving you the maximum amount of information and can be used to narrow
down a problem until you get a dump with useful information.
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.hl 1 The HOTLINE
Finally, when in doubt, CALL THE HOTLINE. We will be quite happy to
assist you.