Tell the person where it hurts
A fault stopped the machine and printed a line to standard error. On a terminal that is a diagnosis. Behind a window it is a frozen picture and no reason at all, because the message went somewhere nobody was looking - the machine looked hung and was not. It had stopped, and said so invisibly. CosmOS catches all five faults now and says what happened on the screen, with the address, in red. A FAULT ENDS THE PROGRAM, NOT THE MACHINE. That is the answer to "carry on or start again", and it is not a compromise: a bare RETI from most of these meets the instruction that failed and fails again, so carrying on was never on offer. But the machine is almost never what is broken. Everything the shell puts back when a program exits - the Stack, its vectors, the drive, the working directory, the console, the screen - is exactly what wants putting back after one dies, so the handler sets a status and joins handleExit. You are back at the prompt, and the program is recorded as having STOPPED rather than finished, because saying "finished" under a red fault message would be the shell contradicting itself. A fault below where programs load is the system's own, and there is nothing to go back to. That one says so and stops. THE SCREEN GOES BACK TO A MODE TEXT CAN BE SEEN IN, and that is the part that matters rather than the part that is prettiest. A program that faulted in bitmap mode left the console with no text rows, so it draws nothing at all: the message would be perfectly correct and completely invisible, which is the one thing it must never be. Two palette entries go back for the same reason, since a program that wrote its own colours can leave every ink the same as every paper. Only the two the message needs, so the rest of what the program chose is left alone. Both halves are checked by looking at the PICTURE, because the serial line was never where the problem was. Crash blind ruins the palette and drops into bitmap mode before it faults; without the mode the screen comes back 320 by 200 with nothing on it, and without the palette it is the right size with the message present and unreadable. Each break loses the red on its own. Crash is also a program worth having: it breaks in whichever of the five ways you name, so a fault screen can be looked at without having written a bug first. Two things found on the way: The native assembler keeps its OWN copy of the reserved vector names, so it did not know NoHandler or NoDevice and built a cosmos.bin that differed from the host assembler's. Caught by native.sh, which is exactly the drift that test exists for. And cosmosMonitor had dead input. It assembles code into 0x8000 and runs it, and that code faults - which used to kill the machine, so everything after it in the file had never run. It runs now, and the recording grew by sixty lines of monitor session that had been unreachable since the day the fault was put there. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
This commit is contained in:
Anachronaut
co-authored by
Claude Opus 5
Claude Opus 5
parent
000a6d39cb
commit
fd9c4c75f8
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; Breaks on purpose, in whichever of the four ways it is asked for.
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;
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; Every one of these used to stop the machine and print a line to a standard error that
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; nobody behind a window is looking at, so the machine appeared to hang. The system catches
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; all of them now and says what happened and where, and this is what says so - and what a
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; person can run when they want to see the fault screen without having written a bug first.
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;
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; Crash opcode a byte in the middle of the code that does not decode
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; Crash service a SWI naming a service the system does not implement
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; Crash bank a transfer out of a bank that has nothing registered in it
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; Crash device asking the console to interrupt, with no handler installed
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; Crash blind the same bad byte, but from a screen with nowhere to print at all
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;
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; The last one is the odd one: it is not something this program does wrong, it is something
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; it fails to have done. The interrupt arrives from outside once the console has anything to
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; say, and with no input it is the END of input that arrives.
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;
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; Written by Anachronaut
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#Include services.asm
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#Program
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#Base 0x4000
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start:
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SETD.0 Argument
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INIB 0d15
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SWI osArgument
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SETD.0 Argument
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SETD.1 WordOpcode
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CALL textSame
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BRQ crashOpcode
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SETD.0 Argument
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SETD.1 WordService
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CALL textSame
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BRQ crashService
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SETD.0 Argument
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SETD.1 WordBank
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CALL textSame
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BRQ crashBank
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SETD.0 Argument
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SETD.1 WordDevice
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CALL textSame
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BRQ crashDevice
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SETD.0 Argument
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SETD.1 WordBlind
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CALL textSame
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BRQ crashBlind
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SETD.0 Usage
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SWI osPrintString
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INIA 0x0A
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OUTA 0x00
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INIA 0x01
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SWI osExit
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; ---- The case the fault screen exists for ----
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;
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; Bitmap mode has no text rows, so the console draws NOTHING there: a program that faults
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; here leaves the system with a message to print and nowhere to print it. Putting the screen
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; back into a mode that has characters in it is the difference between a diagnosis and a
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; machine that appears to have hung.
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crashBlind:
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; ---- And with the colours ruined as well ----
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;
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; A known mode is only half a known screen. This makes the ink of attribute one the same as
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; its paper, which is what a program that wrote its own palette can easily leave behind -
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; and a message printed into that is perfectly present and completely invisible.
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INIA 0d4
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OUTA 0xE3
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INIA 0x30
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OUTA 0xE2
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INIA 0x03
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OUTA 0xE8 ; Video memory as bank four.
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INIA 0d4
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OUTA 0xE3
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INIA 0xFC
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OUTA 0xE4
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INIA 0x40
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OUTA 0xE5 ; 0xFC40, the two entries attribute one draws from.
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RSTA
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INIB 0d8
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crashBlindWipe:
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OUTA 0xE9
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DECB
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BNB crashBlindWipe ; Both of them black, ink and paper alike.
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INIA 0x02
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OUTA 0x31
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crashOpcode:
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0x00 ; Not an instruction, and never will be.
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crashService:
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SWI 0d40 ; Forty is nobody's.
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crashBank:
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INIA 0d9 ; Nothing is registered there.
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OUTA 0xE0
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RSTA
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OUTA 0xE1
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OUTA 0xE2
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INIA 0d1
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OUTA 0xE3 ; Into Data Memory.
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RSTA
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OUTA 0xE4
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OUTA 0xE5
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OUTA 0xE6
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INIA 0d16
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OUTA 0xE7
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INIA 0x01
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OUTA 0xE8 ; Blit, from a bank that is not there.
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crashDevice:
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INIA 0x02 ; Interrupt me when the console has something to say.
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OUTA 0x02
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SIF
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crashWait:
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; Never touches the console, so whatever happens next came from outside.
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BRI crashWait
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#Data
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#Base 0x2000
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WordOpcode:
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"opcode"
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WordService:
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"service"
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WordBank:
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"bank"
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WordDevice:
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"device"
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WordBlind:
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"blind"
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Usage:
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"Crash opcode | service | bank | device | blind"
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Argument:
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#Reserve 0d16
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#Include text.asm
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