MON 312B (octal) - MOINF (CheckMonCall)¶

Checks whether a given monitor call exists in this particular SINTRAN III system. Optional monitor calls are included or left out when SINTRAN is generated; MOINF lets a program probe for one. The caller passes a monitor-call number in A; the normal return means "not implemented" (A = 0), and the skip return delivers the call's entry address in A. ND-100 monitor call.

Status: byte-verified (dispatch + worker body), and the worker's core claim - that it reads MCTAB and returns MCTAB[N] - is now proven from bytes, not merely inferred. All addresses/values are octal.

CORRECTED 2026-07-13, and SPECIAL. MON calls are dispatched through MCTAB @ 005620B (segment 044-S3IDPIT), not the level-14 GOTAB (which is MFELL for 224 of 256 calls). MCTAB[312B] = 032600B = MOINF. Unlike the ordinary MON workers (which live in 003-S3CP), MOINF is part of the monitor-dispatch machinery and lives with the dispatcher in 026-S3IMPIT / 017-S3SMPIT (load 32000B, identical bytes), immediately after CALLP=032201B. In the 003-S3CP overlay the same virtual address 032600B decodes as an unrelated data record table (X103T..X107E), so MOINF must NOT be read there. See ../317B-ExecuteCommand/README.md and SINTRAN/CARVING-HANDOFF.md section 3a.

Full disassembly: 312B-CheckMonCall.ASM.
Emulator model: 312B-CheckMonCall.pseudo.c.

Dispatch path¶

flowchart LR
    A["User program<br/>MON 312B (A = MON#)"] --> B["ENT14 level-14<br/>026-S3IMPIT :072167B"]
    B --> C["GOTAB[312B] = MFELL<br/>:071545B"]
    C --> D["MFELL level switch<br/>:072114B -> CALLP 032201B"]
    D --> E["MCTAB[312B] = MOINF<br/>044-S3IDPIT :006132B = 032600B"]
    E --> F["MOINF worker<br/>026-S3IMPIT :032600B"]
    F --> G["reads MCTAB[MON#]<br/>044-S3IDPIT :005620B + MON#"]
    class A blue
    class B,C,D,E teal
    class F green
    class G teal
    classDef blue fill:#E3F2FD,stroke:#0D47A1,color:#0D47A1
    classDef teal fill:#E0F7FA,stroke:#00838F,color:#00838F
    classDef green fill:#E8F5E9,stroke:#2E7D32,color:#2E7D32

MOINF is both a normal MCTAB-dispatched worker AND itself an MCTAB reader: it returns MCTAB[MON#] for the number the caller asks about.

Code location (dispatch path)¶

Byte offset = (addr - loadbase) in octal words x 2 (decimal). Offsets reproduced with dd.

Role	Segment	Addr (octal)	Byte offset	Symbol	Verdict
MCTAB[312B] slot	044-S3IDPIT.asm	`006132B` = `032600B`	2228	-> `MOINF`	VERIFIED
MOINF worker body	026-S3IMPIT.asm	`032600B-032615B`	768	`MOINF`	VERIFIED
MOINF `MON_COUNT` const	026-S3IMPIT.asm	`032636B` = `000400B`	828	(P+35 datum)	VERIFIED
MOINF `MCTAB` base const	026-S3IMPIT.asm	`032637B` = `005620B`	830	(P+32 datum)	VERIFIED

Verify by hand (from tools/sintran-segment-carver/versions/L-VSX-500/segments/):

dd if=044-S3IDPIT.bin bs=1 skip=2228 count=2 | od -An -tx1   ->  35 80   (= 032600B = MOINF)
dd if=026-S3IMPIT.bin bs=1 skip=768  count=2 | od -An -tx1   ->  d7 8d   (= 153615B, MOINF entry)
dd if=026-S3IMPIT.bin bs=1 skip=828  count=2 | od -An -tx1   ->  01 00   (= 000400B = 256, the bound)
dd if=026-S3IMPIT.bin bs=1 skip=830  count=2 | od -An -tx1   ->  0b 90   (= 005620B = MCTAB base)

(017-S3SMPIT.bin holds identical bytes at the same offsets.)

Instruction walkthrough¶

Full listing: 312B-CheckMonCall.ASM.

032600B IRR 10 DA - read the caller's A register (the MON# argument) across program levels.
032601B LDT 35 - load the bound from the P-relative datum at P+35 = 032636B = 000400B (256) = the number of MON-call slots.
032602B-032603B SKP IF DA MLST ST - continue (in range) only if MON# < 256; else go to the out-of-range path.
032604B-032605B RADD CLD SA DX / LDA I ,X 32 - X := MON#, then load A := mem[ mem[P+32] + X ]. The pointer word at P+32 = 032637B = 005620B = MCTAB base, so this is exactly A := MCTAB[MON#].
032607B RADD CLD 0 DA - out-of-range path sets A := 0 (not implemented).
032610B IRW 10 DA - write the result (MCTAB[MON#] or 0) back to the caller's A.
032611B JAZ - if the result is 0, take the normal return (not implemented).
032612B-032614B IRR 10 DP / AAA 1 / IRW 10 DP - otherwise bump the caller's P by 1: the ND-100 skip return signalling "call implemented".
032615B JMP I 6 - return.

Every one of these steps is byte-proven, including the two constants (256 bound and 005620B MCTAB base) read from the routine's own P-relative data words.

Parameter / register contract¶

Reg / field	Dir	Meaning	Verdict
`A` (caller)	in	monitor-call number to test	VERIFIED (bytes: `IRR 10 DA`)
`A` (caller)	out	`MCTAB[MON#]` = entry address, or `0` if not implemented	VERIFIED (bytes: `IRW 10 DA`)
skip return	out	taken iff entry != 0 (call implemented)	VERIFIED (bytes: `AAA 1` on caller `P`)
MCTAB base `005620B`	const	table base read via P-relative datum at `P+32`	VERIFIED (bytes)
bound `256`	const	range limit read via P-relative datum at `P+35`	VERIFIED (bytes)

Pseudo-code (for an emulator)¶

See 312B-CheckMonCall.pseudo.c - the whole routine is byte-verified, including the MCTAB index and the skip/normal return.

Honest caveats¶

What is byte-proven: essentially the entire call. MCTAB[312B] = 032600B = MOINF; MOINF lives in 026-S3IMPIT (identical in 017-S3SMPIT), reads the caller's MON# via IRR, range-checks it against a 256 bound held at 032636B, indexes MCTAB whose base 005620B is held at 032637B, and returns MCTAB[MON#] (or 0) with the ND-100 skip/normal return convention. This upgrades the NC oracle's claim (that MOINF returns MCTAB[N]) from INFERRED to VERIFIED.

What is NOT proven / noteworthy: nothing material is left unproven for the mechanism. The only subtlety is the overlay trap: reading 032600B in the wrong segment (003-S3CP) yields an unrelated data table, which is what would mislead an analyst - hence the explicit segment note above.

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md · master map: ../../MON-CALL-INDEX.md · NC oracle: SINTRAN/ND500/mon-oracle-for-NC/312B-MOINF_317B-UECOM.md.