AnachronautandClaude Opus 5
000a6d39cb
Dispatching through a vector with nothing in it was the one fault this machine could not hand over, because the thing that would hand it over is the thing that has just found nothing to hand it to. It stopped the machine and no program could do anything about it - so calling a service the system does not implement was fatal, and that is an ordinary mistake to make. Two new fault vectors: 5 when a software vector was empty, 6 when a device interrupted and its hardware entry was. Separate, because they are separate mistakes with separate fixes - one is a program calling something that is not there, the other a program that asked to be interrupted and forgot the handler. WHICH ENTRY WAS EMPTY ARRIVES IN Q, and it is the only thing on this machine a handler is given in a register. Not a fault cause register by another route: the vector still says what happened and Q says which of the 256 entries it happened about, which is a parameter and not a cause. It costs no new state at all, because the frame already saved the Q the interrupted program had and RETI puts it back. The escalation happens once. If vector 5 or 6 is itself empty the machine stops the way it always did, having genuinely run out of places to go. swiFaultTest is what guards that, and it was written long before any of this: it installs nothing, so it must still get the old halt. Breaking the escalation fails the two new tests and not that one; making the escalation unbounded fails that one and not the two new ones. Each break fails exactly the half it belongs to. noDeviceTest is fed no input on purpose. The console raises its line once when input ENDS as well as when a byte arrives - which exists so a program driven by interrupts is told when nothing more is coming - so with no input at all, that end is what turns up. Groundwork for CosmOS's fault screen, which wanted to catch these two and could not. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
57 lines
1.6 KiB
NASM
57 lines
1.6 KiB
NASM
; A software interrupt that names a vector with nothing in it, CAUGHT.
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;
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; That fault used to be the one the machine had no way of handing over, because the thing
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; that would hand it over is the thing that has just found nothing to hand it to. It stopped
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; the machine, and no program could do anything about it - which made calling a service the
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; system does not implement fatal, and that is an ordinary mistake to make.
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;
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; It goes to a vector of its own now, with the number of the empty entry in Q. This catches
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; it, says which one it was, steps over the SWI and its operand, and carries on - so the
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; output says both that the fault arrived and that a program can survive it.
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;
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; Correct output is:
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; empty vector 28
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; carried on
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; and a clean halt.
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#Include console.asm
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#Program
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start:
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SWI 0d40 ; Forty is 0x28, and nothing is installed there.
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SETD.0 Carried
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CALL printString
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CALL newLine
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HALT
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; Entered because there was nowhere to go. Q holds which entry was empty, and it is the only
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; thing on this machine a handler is handed in a register.
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missing:
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SETD.0 EmptyText
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CALL printString
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MVQA
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CALL printByteHex
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CALL newLine
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; ---- Carrying on past it ----
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;
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; The frame holds the address after the SWI and the byte naming its vector, so a bare RETI
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; already lands past the instruction that faulted. That is not true of every fault here -
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; a refused port or a byte that does not decode both resume ON the thing that failed - so
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; it is worth saying out loud which kind this one is.
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RETI
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#Data
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EmptyText:
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"empty vector "
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Carried:
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"carried on"
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#Vectors
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Boot start
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NoHandler missing
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