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MON 045B (octal) - DefineBreakpoint (F1631)

CORRECTED 2026-07-15 (byte-verified). The worker + dispatch described below are on the DEBUNKED model and are WRONG. Byte truth from the carved L07 image: MCTAB[45B] = 005665B = BDBRK=002235B, reached by the real dispatch MON 45B -> ENT14(072167B) -> GOTAB[45B]=MFELL(072114B) -> CALLP(032201B) -> MCTAB[45B]=BDBRK. Verified: dd if=044-S3IDPIT.bin bs=1 skip=1898 count=2 -> 04 9d. NOTE: BDBRK=002235B is below the 003-S3CP load base (030000B), so the worker BODY segment is OPEN (not 003-S3CP); only the MCTAB slot is byte-proven here. Cross-ref ../317B-ExecuteCommand/README.md and SINTRAN/CARVING-HANDOFF.md sec 3a.

Defines / re-arms a symbolic-debugger breakpoint. The byte-verified GOTAB[45] target is a 21-word entry stub (F1631 at 121075B) that forks on the caller arg, edits a breakpoint-table slot, and hands off to a message/queue-send worker family.

Status: level-14 dispatch is byte-proven (GOTAB[45] = 121075B = F1631, re-checkable via prove-mon.py 045); the stub body is real SINTRAN L bytes; worker behaviour is UNVERIFIED and the stub -> worker deeper hops cross an uncarved/low-resident boundary (see Honest caveats). All addresses/values are octal.

Dispatch path

flowchart LR
    A["User program<br/>MON 45B"] --> B["ENT14 level-14<br/>T = MON number"]
    B --> C["GOTAB[45B] = 121075B<br/>(byte + prove-mon proven)"]
    C --> D["F1631 entry stub<br/>025-S3IRPIT :121075B"]
    D -.uncarved / low-resident.-> E["worker family<br/>SNDRE 121640B / PUTPO 115720B"]
    E --> F["slot edit + queue send<br/>via JPL I workers"]
    class A blue
    class B,C,D teal
    class E,F green
    classDef blue fill:#E3F2FD,stroke:#0D47A1,color:#0D47A1
    classDef teal fill:#E0F7FA,stroke:#00838F,color:#00838F
    classDef green fill:#E8F5E9,stroke:#2E7D32,color:#2E7D32

Unlike a two-word MFELL fall-through, GOTAB[45] is a direct dispatch word (121075B, not 000000). The dashed hop is the one link that cannot be followed statically: worker 121211B -> 010341B lands in low resident memory below the carved overlay (load 32000B), runtime-populated.

Code location (dispatch path)

Every row is a real region you can open. Byte offset = (addr - loadbase) in octal words x 2 (decimal).

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[45] dispatch word commoncode.asm - .hex 071300B (1 word) 58752 GOTAB+45 = 121075B VERIFIED
F1631 entry stub 025-S3IRPIT.asm - .hex 121075B-121121B (21 words) 56442 F1631 VERIFIED
general-path worker (A!=3, JPL I 65->121206B) 025-S3IRPIT.asm - .hex 115720B-115737B 53152 PUTPO real bytes; behaviour UNVERIFIED
A==3 worker (JPL I 101->121202B) 025-S3IRPIT.asm - .hex 121640B 57152 SNDRE target VERIFIED; behaviour UNVERIFIED
family ptr 121211B -> low resident - (below load 32000B, uncarved) 010341B - (none) UNVERIFIED

Verify by hand: grep '^71300 ' ../../segments-ref/SINTRAN-DATA_commoncode/SINTRAN-DATA_commoncode.hex -> byte offset 58752; then dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=58752 count=2 | od -An -tx1 -> a2 3d (= big-endian 0xa23d = octal 121075 = the F1631 entry). Then the stub body: grep '^121075 ' ../../segments-ref/025-S3IRPIT/025-S3IRPIT.hex -> offset 56442; dd if=../../../segments/025-S3IRPIT.bin bs=1 skip=56442 count=4 | od -An -tx1 -> b1 40 f2 03 (= octal 130500 171003 = JAN 100 / SAT 3).

Instruction walkthrough

Full listing: 045B-DefineBreakpoint.ASM. Region A is the byte-verified GOTAB[45] target (F1631); region B is the general-path worker (PUTPO).

F1631 arg fork (121075-121104). The stub reads the caller arg in A. 121075 JAN 100 takes an alternate exit (-> 121175) when A is negative. 121076 SAT 3 / 121077 SKP IF DA EQL ST compare A to 3: when A == 3 it calls the worker at 121640B (SNDRE) via 121101 JPL I 101 (pointer word @121202 = 121640); otherwise it falls into the general slot path at 121105B.

Breakpoint-slot handling (121105-121120). 121107 LDX I 76 loads a table base (pointer word @121205 = 061157); 121110 LDA ,X 14 reads slot field 14. 121111 JAZ skips to the next stub (F1632 = 121122B) when the slot is empty. Otherwise 121112-121115 clear four slot fields (STZ ,X 14/46/4/2) - consistent with releasing / re-arming a breakpoint record before it is (re)written - and 121117 LDD ,X 15 loads the slot descriptor.

Worker hand-off (121121). 121121 JPL I 65 calls the general-path worker at 115720B (PUTPO, pointer word @121206 = 115720).

Worker body PUTPO (115720-115737). 115720 IOF opens an I/O-off critical section; 115721 JXZ skips the edit when X == 0; 115726 STDTX / 115731 STATX store a double and a single word into an X-indexed table; 115736 ION / 115737 EXIT close the section. Structurally a queue/table update - the exact DefineBreakpoint meaning of each field is UNVERIFIED.

Parameter / register contract

Reg / field Dir Meaning Verdict
A (ZAREG) in selector: <0 -> alt exit; ==3 -> SNDRE worker; else slot path VERIFIED (branch structure)
X base in breakpoint-table base (from ptr @121205 = 061157) VERIFIED (bytes); encoding inferred
slot fields 2,4,14,46 out cleared (STZ ,X) during slot handling VERIFIED (from code)
slot field 15 (double) in slot descriptor loaded (LDD ,X 15) before worker call VERIFIED (from code)
workers 121640B/115720B - shared subroutines invoked via JPL I VERIFIED targets; behaviour UNVERIFIED
010341B (via 121211B) - low-resident, runtime-populated hop UNVERIFIED
skip / error return out not resolvable from the 21-word stub alone UNVERIFIED

The user-visible register convention lives in the caller-side MON 45 wrapper and the deeper (uncarved / low-resident) worker frames, so the precise A/X/T meaning is inferred, not byte-proven here. Error codes cited by earlier drafts (174/274/371/372/400) are NOT derivable from these bytes -> UNVERIFIED.

Pseudo-code (for an emulator)

See 045B-DefineBreakpoint.pseudo.c - a pseudo-C model of the handler for emulator authors. The F1631 stub control flow (the A==3 fork, the four-field slot clear, the two JPL I worker hand-offs) is byte-verified; the worker semantics (breakpoint slot vs queue send) are inferred from the call structure.

Every instruction in the .pseudo.c is translated against the canonical ND100-INSTRUCTION-SEMANTICS.md (bare LDx/LDT/AND disp = P-relative mem[P+disp], not literals; SKP/BSKP skip polarity; RADD CLD SD DA = A = D; T/X transfers = physical EL).

Honest caveats

What is byte-proven: GOTAB[45] = 121075B = F1631 (level-14 direct dispatch, matches a re-runnable prove-mon.py 045); the F1631 stub at 121075B is real, non-zero code (130500 171003 140065 ...); its worker pointer words (@121202 = 121640, @121206 = 115720) are real bytes and land inside the carved 025-S3IRPIT overlay.

What is NOT proven: the behaviour of MON 45 end to end. The F1631 workers resolve to a message/queue-send family (SNDRE / PUTPO / SNDWT / SNDBU / CREME / REDOM per SYMBOL-2-LIST) whose exact role in DefineBreakpoint is not derivable from these bytes; and 121211B -> 010341B leaves the carved image entirely into low resident memory (below load 32000B), runtime-populated. Symbol NAMES come from SYMBOL-2-LIST (SYMBOL-1-LIST, which meta names for segment 025, has NO entry for these addresses - a revision mismatch), so treat octal addresses as truth and names as hints.

Reconciling the old carve (one clear story): earlier drafts of this folder carved the 16-way symbolic-DEBUGGER dispatcher (105075B) and the BRPNT breakpoint-trap head (104554B). Those are genuine SINTRAN L bytes but are MISATTRIBUTED to MON 45: a full scan of GOTAB[0..377] finds NO entry equal to 105075B or 104554B, the value 105075/104554 appears zero times as a pointer word anywhere in 025-S3IRPIT, and the F16xx stub family (~121xxx) is ~14000 words away - far outside the 8-bit P-relative reach of any stub. BRPNT is entered by a breakpoint trap (a planted breakpoint firing), and DEBUGGER by a resident second-level / CALLPROC dispatch not visible in GOTAB - not by MON 45. The byte-truth handler for MON 45 is F1631, carved here. Confirming the full path needs a live trace (break at 121075B on a real MON 45, single-step through the worker and capture the runtime 010341B dereference).

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md - dispatch reality: ../../TASK-05-mismatches.md - master map: ../../MON-CALL-INDEX.md.