Breakpoints: SWI osBreak, and s refuses a read only bank
A breakpoint that shows every register as the program had them, waits for a key, and carries on. NOTHING IS OVERWRITTEN, and that is the design rather than a shortcut. A breakpoint poked into a running program has to replace an instruction, and putting that instruction back in order to continue is the same act as disarming the breakpoint; firing a second time would mean stepping over the restored instruction and putting the breakpoint back behind it, and this machine cannot step a single instruction. SWI is two bytes, dispatches through a vector, and its frame already holds the address after it, so RETI resumes at the next instruction with nothing to restore and nothing to re-arm. It fires every time it is reached. The price is that a breakpoint is part of the program: a build with them in has different addresses from a build without. That is the bargain every machine with a break instruction makes. Every value shown comes out of the frame rather than the registers, because by the time the handler runs the registers are the handler's. Apps/Break.asm stops twice so that the second stop is checked as well as the first. Also here, found by the test that came with it: the monitor's s wrote into whichever bank was selected, and bank 2 is the controller's own table, published read only. Writing to it was refused, and a refusal nobody catches stops the machine - so selecting the bank table to look at it and then typing s killed the session. bankPresent now keeps the whole flags byte and s declines. The recorded output of cosmosMonitor had contained that crash, having been blessed without being read. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Anachronaut
co-authored by
Claude Opus 5
Claude Opus 5
parent
b36d438132
commit
5fd995aa62
@@ -0,0 +1,16 @@
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CosmOS
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> loaded, starting at 2000
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> two stops, and what the registers were at each
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break at 200E
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A 11 B 22 Q 00 S 00
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DP0 1030 DP1 05CC DP2 039A DP3 2000
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press a key
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break at 2018
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A 44 B 55 Q 00 S 00
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DP0 1000 DP1 05CC DP2 039A DP3 2000
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press a key
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carried on to the end
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finished
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> halted
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Execution halted.
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[exit 0]
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@@ -26,6 +26,35 @@ CosmOS
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0010 03 FF 08 00 00 00 00 00 01 20 01 00 00 00 00 00 ......... ......
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0020 00 FF 00 00 00 00 00 00 00 FF 00 00 00 00 00 00 ................
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0030 00 FF 00 00 00 00 00 00 00 FF 00 00 00 00 00 00 ................
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* Fault: The device on port 233 refused the access at Program Address 0x1359, and nothing is installed to deal with it.
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* that bank will not be written
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* bank 00
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* * 8000 26 48 INIA 48
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8002 D1 00 OUTA 00
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8004 26 0A INIA 0A
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8006 D1 00 OUTA 00
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8008 18 12 SWI 12
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800A 00 ADD
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800B 00 ADD
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800C 00 ADD
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* H
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finished
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* 8000 26 48 INIA 48
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8002 D1 00 OUTA 00
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8004 26 0A INIA 0A
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8006 D1 00 OUTA 00
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8008 18 12 SWI 12
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800A 00 ADD
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800B 00 ADD
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800C 00 ADD
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* > greet.sbx 210
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hello.sbx 52
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Life.sbx 1411
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Snake.sbx 2175
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Keys.sbx 663
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Say.sbx 155
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Break.sbx 128
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notes.txt 21
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8 files
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> halted
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Execution halted.
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[exit 1]
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[exit 0]
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@@ -6,8 +6,9 @@ Life.sbx 1411
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Snake.sbx 2175
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Keys.sbx 663
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Say.sbx 155
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Break.sbx 128
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notes.txt 21
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7 files
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8 files
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> load what?
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> no such file
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> not a program
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@@ -0,0 +1,5 @@
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load Break.sbx
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run
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exit
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@@ -9,6 +9,8 @@ b data
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x 1000
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b 2
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x 0
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s 0 FF
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b program
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s 8000 26 48 D1 00 26 0A D1 00 18 12
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d 8000
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g 8000
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@@ -91,6 +91,11 @@ for i in 1 2 3 4 5 6 7 8; do "$TOOL" put "$DISKS/sbfs.img" "filler$i.txt" >/dev/
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"$ROOT/Assembler" -I "$ROOT/Programs/CosmOS/Source" \
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"$ROOT/Programs/CosmOS/Apps/Say.asm" -o "$WORK/Say.sbx" >/dev/null
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"$TOOL" put "$DISKS/cosmos.img" "$WORK/Say.sbx" >/dev/null
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# Break.sbx stops itself twice and shows what the registers were each time. It needs no disk
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# of its own: it only prints.
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"$ROOT/Assembler" -I "$ROOT/Programs/CosmOS/Source" \
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"$ROOT/Programs/CosmOS/Apps/Break.asm" -o "$WORK/Break.sbx" >/dev/null
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"$TOOL" put "$DISKS/cosmos.img" "$WORK/Break.sbx" >/dev/null
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printf 'this is not a program' > notes.txt
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"$TOOL" put "$DISKS/cosmos.img" notes.txt >/dev/null
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@@ -221,6 +221,10 @@ cosmosRun | CosmOS/Source/cosmos.asm | run | cosmosRun
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# The last part is what the mode is FOR: a program typed in as bytes, run with g, and the
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# prompt that comes back is the monitor's own. A program giving the machine back lands where
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# it was started from, so looking at something and running it do not interrupt each other.
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#
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# It also asks to write into bank 2, the controller's own table, which is published read
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# only. That used to stop the machine, and the recorded output of this test contained the
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# crash without anybody noticing, which is what blessing a result without reading it buys.
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cosmosMonitor | CosmOS/Source/cosmos.asm | run | cosmosMonitor.in | - | disks/cosmos.img
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# The original hello.asm, brought over as an application. It is not much of a program,
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# but it is the one that talks to the hardware directly: it writes to port 0x00 instead
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@@ -270,6 +274,13 @@ cosmosFiles | CosmOS/Source/cosmos.asm | run | cosmosFil
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# name, and with several words, since what arrives is the rest of the line rather than a
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# list and it is the program's business what to make of it.
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cosmosSay | CosmOS/Source/cosmos.asm | run | cosmosSay.in | - | disks/cosmos.img
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# A program stopping itself to be looked at. Two breakpoints, so what is checked is not only
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# that one fires but that the SECOND one does - which is the whole difference between this
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# design and one that overwrites an instruction, since an overwritten instruction has to be
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# put back to continue and putting it back is the same act as disarming the breakpoint.
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# Every value shown comes out of the interrupt frame rather than the registers, because by
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# the time the handler runs the registers are the handler's.
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cosmosBreak | CosmOS/Source/cosmos.asm | run | cosmosBreak.in | - | disks/cosmos.img
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# The editor, which is the first program on this machine that makes a file a person typed:
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# every byte on every other image here was put there by the host tool. It is run twice in
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# one session, and that is the test rather than a flourish - the second run reads back what
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@@ -291,6 +302,7 @@ app-Life | CosmOS/Apps/Life.asm | assemble | -
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app-Snake | CosmOS/Apps/Snake.asm | assemble | - | -
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app-Keys | CosmOS/Apps/Keys.asm | assemble | - | -
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app-Say | CosmOS/Apps/Say.asm | assemble | - | -
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app-Break | CosmOS/Apps/Break.asm | assemble | - | -
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app-Edit | CosmOS/Apps/Edit.asm | assemble | - | -
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app-Files | CosmOS/Apps/Files.asm | assemble | - | -
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