AnachronautandClaude Opus 5
3449405b18
CosmOS had 1,161 bytes of Program Memory left before the address applications load at, and Tab completion is not going to fit in that with anything to spare. So the wall moves up one page: the system keeps below 0x4FFF and 0x2FFF, and an application is based at 0x5000 and 0x3000. A PAGE IS A CHEAP THING TO GIVE IT AND AN EXPENSIVE THING TO RUN OUT OF. An application still has 44K of Program Memory before the vector table and the largest one here uses 7.5K, so what was taken from applications is space nothing has ever asked for - while what the system gained is the difference between building the next thing and counting bytes while building it. Not doubling, which was the version that would have cost application space worth minding. One page, and the same again when it is needed. Nothing in the machine knows where the wall is, so this is 34 #Base lines, one threshold in the fault handler, and the table in the CosmOS README that Tests/docs.sh reads its limits out of. The native assembler's scratch map had to move with it, and docs.sh said so before anything ran: its data reached 0x40D6 and its buffers began at 0x4000, so they were sitting on its variables. That file already carries a paragraph about the floor coming up and the map staying where it was. It has happened twice now, and been caught by a check the first time wrote. Twenty three recordings are the same runs a page higher. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW
85 lines
2.7 KiB
NASM
85 lines
2.7 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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;
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; EVERY POINTER IS SET BEFORE EACH STOP, and the three this program owns are rotated
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; between the two so that all of them visibly change.
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;
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; This program used to leave DP1 and DP2 alone, and what a stop then showed for them was
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; whatever the shell happened to have left there. That is a real thing about the machine -
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; a program is handed the pointers as it finds them - but it is not this program's to
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; demonstrate, and it made what this program prints depend on where CosmOS's code happens
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; to sit. The recorded output had to be taken again four times in one day's work, every
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; time for a value nothing should ever depend on.
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;
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; A demonstration of what the registers were should show registers somebody chose. Then
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; every line of it is being asserted rather than merely observed.
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;
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; DP3 is deliberately still the system's. It is where the program was entered, which is the
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; one thing here worth seeing that this program did not choose, and it is steady because it
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; is this program's own base.
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#Include services.asm
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#Program
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#Base 0x5000
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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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SETD.1 Banner
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SETD.2 DoneText
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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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RSTA
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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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SETD.1 DoneText
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SETD.2 Marker
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SWI osBreak
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RET
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#Data
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#Base 0x3000
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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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