page@ulowell.UUCP (Bob Page) (03/20/86)
(I picked this up off of Quantum Link, aka the Amiga Information Network.)
(I cannot vouch for its accuracy, but thought you might be interested. )
"You Too Can Be An Amiga Guru!"
by Dave Boulton
('New & Improved' version as of 11 Feb 86)
Arrrrrrgh!, you snarl as the dreaded System Request box pops on to
the Workbench screen:
Software error - task held
Finish ALL disk activity
Select CANCEL to reset/debug
You stare at the computerese for a moment, and then hit the CANCEL
button. The current screen is pushed down and you find yourself
staring at the orange and black finality of:
Software Failure. Press left mouse button to continue.
Guru Meditation #02010009.00009310
Many have wondered what the cryptic digits of the Guru Meditation
Number were all about. Perhaps the flashing orange box has some
strange mystical hypnotic powers. On the other hand, perhaps the
number is some sort of digitized mantra which allows the Yogis of
Los Gatos to attain perfect enlightenment. Whatever the
interpretation was, it was beyond the reach of the average user.
The most that the user is ever told is 'Not enough memory' or
maybe 'Software Failure'.
In fact, the Guru Meditation Number (or simply 'alert number')
distills a lot of information about exactly what mishap has
befallen your Amiga. To those able to decipher it, the alert
number tells a great deal about who did what to whom as the
machine crashed. Not that there is much that can be done about the
situation after the fact; the information is mainly useful to help
the Software Gurus in debugging their programs or in diagnosing
what caused the fatal situation. It is a kind of post-mortem
report, explaining why the patient died.
But there are times when it would be valuable to the user to know
precisely what happened to cause a crash. Other times, you may
just be curious as to what was going on. All of the Alerts (the
correct name for a Guru Meditation box) are defined in the header
file called "exec/alerts" provided to software developers. What
follows is an attempt at translating that information into a first
order approximation of English.
Many of the error conditions that the Amiga OS detects are deeply
intertwined with the various internal data structures and
operating system calls. There isn't any way that I can define all
of the terms used without reprinting most of the ROM Kernel Manual
here in the newsletter. However, if you are familiar with the
basics of how the system software works, then you can figure out a
great deal about why a particular program has crashed.
Specific error code -----+ +--- Task Address
| |
02 01 0009 . 00009310
| |
Subsystem number -+ +--- General error code
An alert number is divided into several parts. The section to the
right of the decimal point is simply the address in RAM of the
task that was running when the error occurred. This helps tell
someone who is debugging a program which of the many different
programs running in the Amiga caused the problem. In the example
given above, the running task was at 9310 hex. In this case that
happens to mean that the error occurred in CLI process number 1.
If I had been debugging a complex program which uses several
tasks, this information would be useful. As it happens, all it
tells me here is that the problem was in my software, not in any
of the system tasks.
The left hand portion of the alert number is an encoded error
number. There are several fields with different meanings:
The first two digits tell which module of the operating system
reported the error (this is technically known as the 'alert
object' or a Subsystem ID). In the example above the alert object
is 02, which tells me that the error was reported by the Graphics
library.
The first digit can be encoded in a funny way. The 'most
significant bit' of this digit says whether or not this alert is a
'dead-end'; that is, does the system have a chance of recovering
from the error or not. If the alert object had been given as 82
instead of 02, then the alert would be a 'dead-end'.
In practice, this is a pretty narrow distinction. By the time you
have gotten to the Alert Box the system is in such dire straits
that the only choices left are to reboot, or to enter the system
debugger. The 'dead-end' bit could possibly cause some confusion
if you aren't used to dealing in hexadecimal. If the first digit
of the alert object is ever greater than 7 (hexadecimal) then
subtract 8 from it. Thus if the first two digits were B1, then the
alert is a dead-end error reported by the Workbench (Subsystem ID
code 31). (B minus 8 equals 3, for those of you without the
required 16 fingers!)
The Subsystem ID codes are as follows:
Exec Library 01 Console Device 11
Graphics Library 02 GamePort Device 12
Layers Library 03 Keyboard Device 13
Intuition Library 04 TrackDisk Device 14
Math Library 05 Timer Device 15
CList Library 06 CIA Resource 20
DOS Library 07 Disk Resource 21
RAM Library 08 Misc Resource 22
Icon Library 09 BootStrap 30
Audio Device 10 Workbench 31
The next two digits specify the general type of error which has
occurred. For many specialized types of errors this field is 00,
instead of one of the general error codes below. This field is
often very useful, since the user can easily tell such things as
out-of-memory conditions, and missing libraries or device drivers
(if you have deleted files from the LIBS or DEVS directories of
your boot disk). In the example given above the general error code
is 01, which means the the Graphics Library was not able to find
enough free memory to allocate for some reason.
The general error codes are:
Insufficient memory 01 OpenDevice error 04
MakeLibrary error 02 OpenResource error 05
OpenLibrary error 03 I/O error 06
The last four digits of the alert number give specific information
about exactly what error has occurred. The interpretation of the
specific error code depends on which subsystem we are talking
about. Each subsystem reuses the same values for the specific
error code with different meanings. In our example the specific
error code is 0009. Since we are talking about an error in the
graphics library, we determine that the error is called
'TextTmpRas' which means that a call to the Text() routine (trying
to draw characters on the screen) ran out of memory when it tried
to allocate memory for a TmpRas (temporary raster work area) data
structure.
If the error had been in a different subsystem (say the Intuition
library) then the same error code of 0009 would have had a
completely different interpretation (for Intuition it would mean
that the Screen Type parameter to an OpenScreen call was not a
valid type).
There is one special case in dealing with Guru Meditation Numbers.
Everything that we have discussed so far has to do with alerts
that are detected and generated by the Amiga ROM Kernel. There is
another case, which is when an alert is caused by a 68000
processor exception (or 'trap'). Whenever a CPU trap occurs (for
instance, an illegal opcode is executed) the Exec will generally
cause an alert. A program can intercept this trap processing, and
insert its own 'trap handler' to perform some other function, but
usually these traps end up causing an alert. When this happens,
the left hand part of the guru number will be a small value. The
subsystem ID and the general error code will both be zero. The
specific error code will be the 'trap number' of the trap that
occurred. The trap numbers are part of the 68000 chip, and are not
assigned by the ROM kernel like other error codes are.
The following is a list of all the possible CPU traps. A few of
these will never show up as an alert because they are always
handled by the ROM Kernel. I list all of them here for
completeness (and just in case I'm wrong, and they ever _do_ show
up).
Bus Error 02 Priviledge Violation 08
Address Error 03 Instruction Trace 09
Illegal Instruction 04 Line A Emulation 0A
Divide by Zero 05 Line F Emulation 0B
CHK instruction 06 TRAP 0 ... 15 20 ... 2F
TRAPV (Overflow) 07
The following is a list of the specific error codes and a short
comment about their meaning. The descriptions are a slightly
edited version of the exec/alerts file, so they are very cryptic.
Exec Library
ExcptVect 81000001 CPU trap vector checksum
BaseChkSum 81000002 ExecBase checksum error
LibChkSum 81000003 library checksum failure
LibMem 81000004 no memory to make library
MemCorrupt 81000005 corrupted free memory list
IntrMem 81000006 no memory for interrupt servers
Graphics Library
CopDisplay 82010001 copper display list, no memory
CopInstr 82010002 copper instruction list, no mem.
CopListOver 82000003 copper list too long
CopIListOver 82000004 copper intermediate list too long
CopListHead 82010005 copper list head, no memory
LongFrame 82010006 long frame, no memory
ShortFrame 82010007 short frame, no memory
FloodFill 82010008 flood fill, no memory
TextTmpRas 02010009 text, no memory for TmpRas
BltBitMap 8201000A BltBitMap, no memory
Intuition Library
GadgetType 84000001 unknown gadet type
CreatePort 84010002 create port, no memory
ItemAlloc 84010003 item plane alloc, no memory
SubAlloc 84010004 sub alloc, no memory
PlaneAlloc 84010005 plane alloc, no memory
ItemBoxTop 84000006 item box top < RelZero
OpenScreen 84010007 open screen, no memory
OpenScrnRast 84010008 OpenScreen's AllocRast, no mem.
SysScrnType 84000009 open sys screen, unknown type
AddSWGadget 8401000A add SW gadgets, no memory
OpenWindow 8401000B open window, no memory
BadState 8400000C Bad State Return entering Int.
BadMessage 8400000D Bad Message received by IDCMP
WeirdEcho 8400000E Weird echo causing problem
NoConsole 8400000F couldn't open the Console Device
DOS Library
StartMem 07010001 no memory at startup
EndTask 07000002 EndTask didn't
QPktFail 07000003 Qpkt failure
AsyncPkt 07000004 Unexpected packet received
FreeVec 07000005 Freevec failed
DiskBlkSeq 07000006 Disk block sequence error
BitMap 07000007 Bitmap corrupt
KeyFree 07000008 Key already free
BadChkSum 07000009 Invalid checksum
DiskError 0700000A Disk Error
KeyRange 0700000B Key out of range
BadOverlay 0700000C Bad overlay
TrackDisk Device
TDCalibSeek 14000001 calibrate: seek error
TDDelay 14000002 delay: error on timer wait
Timer Device
TMBadReq 15000001 bad request
Disk Resource
DRHasDisk 21000001 get unit: already has disk
DRIntNoAct 21000002 interrupt: no active unit
BootStrap
BootError 30000001 boot code returned an error
*** End of File ***