AnachronautandClaude Opus 5
588e02aff5
The memory map gave CosmOS 0x0000 through 0x1FFF of Program Memory and applications 0x2000 and above. CosmOS is 8141 bytes at the previous commit, which is fifty one bytes short of the line, and the next thing added to it went over. GOING OVER DOES NOT FAIL WHERE IT HAPPENS. Nothing enforces the division: an application says where it goes with #Base and the loader puts it there, so a CosmOS that has grown past 0x1FFF simply has the next program loaded written over the end of it. What breaks is whichever part of the shell that program happened to cover, at whatever later moment somebody uses it. It turned up here as the monitor's assemble command answering "I do not know" to valid instructions, several commands into a session, on a machine that had booted perfectly well. Both halves are doubled: applications now start at 0x4000 in Program Memory and 0x2000 in Data Memory. That is 16K of code and 8K of data for the system, against the 8775 and 2948 it uses today. Both were on the same trajectory, and moving them together means the twenty files that say #Base are edited once rather than twice. The standalone loader's loadable.asm keeps its old base: it belongs to the loader CosmOS grew out of, not to CosmOS, and its addresses answer to a different program. The unbased-segment diagnostic keeps its old base too - it exists to produce an error message that names the address, and the message is what is recorded. Tests/docs.sh now reads the two limits out of the table in the README and measures both segments against them. It reads them rather than being told them because the table is the specification, and this is the second time in this project that the thing nobody checked is the thing that rotted. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
63 lines
1.7 KiB
NASM
63 lines
1.7 KiB
NASM
; Stopping a program to look at it.
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;
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; SWI osBreak shows every register as this program had them, waits for a key, and carries
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; on. It is two bytes and it fires every time it is reached.
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;
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; WHY IT IS AN INSTRUCTION RATHER THAN SOMETHING SET FROM OUTSIDE. A breakpoint that was
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; poked into a running program would have to overwrite an instruction, and then putting that
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; instruction back in order to continue is the same act as disarming the breakpoint. Firing
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; a second time would mean stepping over the restored instruction and putting the breakpoint
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; back behind it, and this machine cannot step one instruction. Nothing is overwritten here,
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; so there is nothing to restore and nothing to re-arm.
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;
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; The price is that it is part of the program. A build with breakpoints in it has different
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; addresses from a build without, which is the same bargain every machine makes that has a
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; break instruction.
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;
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; Correct output is two stops. A and B differ between them, the addresses differ, and the
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; Stack Pointer differs too, because the second one is inside a subroutine and a call has
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; put ten bytes down by then.
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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 Banner
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SWI osPrintString
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INIA 0d17
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INIB 0d34
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SETD.0 Marker
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SWI osBreak
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; The second stop is inside a subroutine, so that the Stack Pointer is visibly not where
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; it was: a call puts ten bytes down before this one gets there.
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CALL deeper
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SETD.0 DoneText
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SWI osPrintString
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SWI osExit
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deeper:
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INIA 0d68
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INIB 0d85
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SETD.0 Banner
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SWI osBreak
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RET
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#Data
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#Base 0x2000
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Banner:
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"two stops, and what the registers were at each
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"
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Marker:
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"marker"
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DoneText:
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"carried on to the end
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"
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