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MON 305B (octal) — GetSIBASMessage (MSIBB)

Retrieves a message from the SIBAS database system — the server-side of the SIBAS inter-process communication over RT-common. It is the receive/get counterpart of MON 304B SendSIBASMessage; the two share one SIBAS handler body (MAPSI = send, MSIBB = get, TISIB = timer). Internal-use call (manual ND-860228.2 EN, section 2.14, name-only).

Status: the GOTAB dispatch word is byte-proven, but it does not point at the SIBAS handler. GOTAB[305] = 111752B (byte-proven) lands on DIA0, the head of the DIA device/DIA-block body — the same body the MON 304B DSI0 stub jumps into. The semantic MSIBB SIBAS worker is real SINTRAN L bytes but is unreachable from GOTAB[305] and from every GOTAB slot 0..377 — it is reached only across the uncarved resident CALLPROC bridge (see Honest caveats). All addresses/values are octal.

Dispatch path

flowchart LR
    A["User / system program<br/>MON 305B"] --> B["ENT14 level-14<br/>T = MON number"]
    B --> C["GOTAB[305B] = 111752B<br/>(byte-proven)"]
    C --> D["DIA0 device/DIA-block body<br/>025-S3IRPIT :111752B<br/>MISATTRIBUTED (not SIBAS)"]
    C -.uncarved CALLPROC.-> E["MSIBB SIBAS-get worker<br/>025-S3IRPIT :104221B<br/>real SINTRAN L bytes"]
    class A blue
    class B,C teal
    class D orange
    class E 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
    classDef orange fill:#FFF3E0,stroke:#E65100,color:#E65100

The solid edge (C → D) is byte-proven: GOTAB[305] = 111752B = DIA0. The dashed hop (C ⇢ E) is the resident CALLPROC/second-level dispatch to the semantic MSIBB SIBAS handler — it is not present in any carved segment, so it is the one link that cannot be followed statically. This mirrors MON 304B exactly: 304B's GOTAB points at DSI0 (which jumps into DIA0), 305B's GOTAB points at DIA0 directly.

Code location (dispatch path)

Ground truth: python3 scripts/prove-mon.py 305 → GOTAB[305] = 111752B (the stored word 93 ea). Byte offset of octal address A in a segment with load base L: word = (A − L) in octal, byte = word × 2 (decimal).

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[305] dispatch word commoncode.asm · .hex 071540B (1 word) 59072 GOTAB+305 = 111752B VERIFIED (raw word 93 ea)
DIA0 device/DIA-block body 025-S3IRPIT.asm · .hex 111752B–112113B 49108 DIA0 bytes VERIFIED; MISATTRIBUTED (issues MON 131/64/116/134 — RT-level device code, not SIBAS)
resident CALLPROC bridge — (uncarved) — — CALLPROC UNVERIFIED
MSIBB SIBAS-get worker body 025-S3IRPIT.asm · .hex 104221B–104314B 43298 MSIBB (sibling of MAPSI/TISIB) real bytes; link MISATTRIBUTED (unreachable from GOTAB[305] and every slot 0..377)

Verify by hand: grep '^71540 ' ../../segments-ref/SINTRAN-DATA_commoncode/SINTRAN-DATA_commoncode.hex → 71540 111752 223 352 59072 (word 111752B, byte offset 59072); then dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=59072 count=2 2>/dev/null | od -An -tx1 → 93 ea. For the MSIBB worker head: dd if=../../../segments/025-S3IRPIT.bin bs=1 skip=43298 count=6 2>/dev/null | od -An -tx1 → cc 7b f1 04 d0 87 (= octal 146173 170404 150207 = RADD CLD SX DB / SAA 4 / MCL PIE, the MSIBB entry). For the DIA0 target head: dd if=../../../segments/025-S3IRPIT.bin bs=1 skip=49108 count=6 2>/dev/null | od -An -tx1 → f5 31 09 2a 48 4b (= octal 172461 004452 044113 = AAA 61 / STA ,B 52 / LDA 113).

Instruction walkthrough

Full listing: 305B-GetSIBASMessage.ASM. Two regions.

Region A — the byte-proven GOTAB target (DIA0 body). GOTAB[305] = 111752B = DIA0. This is the DIA device/DIA-block body (111752B–112113B): it reads a status/flags word (111771 LDT ,B 33), branches on its bits, and on the main path does a block transfer (112016 ION / 112021 MON 131 ABSTR/DataTransfer / 112023 IOF). Its error path (112077–112112) issues MON 64 (ERMSG), MON 116 (UNFIX) and MON 134 (RTEXT); the tail (112055–112064) uses IRW 20 DP / MST PID (RT scheduling). ANOMALY: issuing MON and using IRW/MST PID is resident RT-program/driver behaviour, not clean level-14 handler code — hence the DIA0 semantics are UNVERIFIED and the SIBAS-get attribution is MISATTRIBUTED.

Region B — the semantic SIBAS-get handler (MSIBB). MSIBB at 104221B decodes as a clean level-14 SIBAS handler and issues no MON instructions. It copies the index register into B (104221 RADD CLD SX DB = B = X), sets MLEV (104222 SAA 4 / 104223 MCL PIE), masks and tests the SIBAS device word (104224 LDA ,B 11, 104225 SHA ZIN SHR 6, 104231 SKP IF DA UEQ ST), locates the message-buffer head (104250 LDX I ,X 41), walks the buffer chain (104254 LDX ,X 1 … 104257 BSKP ONE 170 DA), stages a reply record and status word, and returns via an indirect link cell (104303 JMP I 10 → 104313). The words 104304B–104314B are the routine's local pointer/constant block (data — nd100-dis renders them as instructions). MAPSI=103675B (send) and TISIB=104315B (timer) are sibling entries in the same body. This matches the NPL SUBR MAPSIB,MSIBB,TISIBB structure — but it is not what GOTAB[305] reaches.

Parameter / register contract

Reg / field Dir Meaning Verdict
entry point (worker) in MSIBB=104221B (SIBAS-get); siblings MAPSI=103675B, TISIB=104315B VERIFIED (bytes)
device word (,B 11) in SIBAS device selector (masked/shifted 104225/104235/104246) VERIFIED masking; slot meaning inferred
HOINT (,B -1) in/out device interrupt word (104233 STA ,B -1) VERIFIED store; meaning inferred
buffer head (X) internal message-buffer chain head (104250 LDX I ,X 41), walked via LDX ,X 1 VERIFIED (bytes)
status/result (,B 12) out caller status word branched on at 104263, staged into the reply VERIFIED store; meaning inferred
GOTAB target dispatch GOTAB[305]=111752B → DIA0, not MSIBB VERIFIED (byte-proven)

The user-visible register convention lives in the caller-side MON 305 wrapper and the uncarved CALLPROC frame, so the precise A/X/T assignment for MSIBB is inferred, not byte-proven. Full YAML contract: Developer/MON/calls/305B_GetSIBASMessage.yaml (names MSIBB as the handler).

Pseudo-code (for an emulator)

See 305B-GetSIBASMessage.pseudo.c — a pseudo-C model with BOTH paths: dispatch_DIA0() (the byte-proven GOTAB target, RT-level semantics UNVERIFIED) and mon_get_sibas_message() (the semantic MSIBB SIBAS-get handler). Control flow and the buffer-chain walk are byte-verified; the register/parameter labels are inferred from the NPL structure.

Every instruction in the .pseudo.c is translated against the canonical ND100-INSTRUCTION-SEMANTICS.md (RADD CLD SX DB = B = X — the COPY idiom, dest cleared then source added; SHA ZIN SHR 6 = logical right shift A by 6 with zero fill; SKP IF DA UEQ ST = skip if A != T unsigned; LDX ,X 1 = X = mem[X + 1] chain follow; BSKP ONE 170 DA tests bit 15 of A, the printed bit number being bn<<3).

Honest caveats

What is byte-proven: GOTAB[305] = 111752B (matches a live read of the running system via prove-mon.py); 111752B is DIA0, the head of the DIA device/DIA-block body (the same body MON 304B's DSI0 stub jumps into); and the MSIBB worker entry bytes at 104221B are real SINTRAN L bytes that decode as a clean SIBAS-get handler.

What is NOT proven — one story: GOTAB[305] points at DIA0, RT-level device code (MON 131/64/116/134, IRW/MST PID), not at the SIBAS handler. Three independent byte checks show MSIBB is unreachable from it: 1. DIA0 (111752) → MSIBB (104221) is ~5500B words apart — far outside any ND-100 relative JMP/JPL displacement, so no direct edge is possible. 2. A full word-scan of 025-S3IRPIT.bin for any word equal to 104221/103675/104315 (an absolute JMP I/JPL I pointer to MSIBB/MAPSI/TISIB) returns zero matches. 3. A full GOTAB[0..377] scan for any value inside the MSIBB window returns none — no MON call 0..377 dispatches to the carved worker.

So MSIBB is real code reached only through the resident CALLPROC second-level dispatch, which lives in an uncarved overlay — hence MISATTRIBUTED in the strict byte sense. Confirming it needs a live level-14 trace: break on a real MON 305B, capture the first PC after the trap, and see whether it lands on 111752B (DIA0), 104221B (MSIBB), or enters CALLPROC then a second-level table.

Address note: the NPL source is a different revision. Match behaviour/structure, not raw bytes. The L07 SYMBOL-2-LIST places MSIBB=104221B, MAPSI=103675B, TISIB=104315B as three sibling entries of one SIBAS body, exactly the NPL SUBR MAPSIB,MSIBB,TISIBB.

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