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MON 015B (octal) - Undocumented (F1615)

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[15B] = 005635B = SETUP=103417B in segment 006-S3FS, reached by the real dispatch MON 15B -> ENT14(072167B) -> GOTAB[15B]=MFELL(072114B) -> CALLP(032201B) -> MCTAB[15B]=SETUP. Any "GOTAB from commoncode" / "uncarved CALLPROC bridge" / "F16xx stub" / old worker name below is an artefact of the wrong table. Verified: dd if=044-S3IDPIT.bin bs=1 skip=1850 count=2 -> 87 0f. Cross-ref ../317B-ExecuteCommand/README.md and SINTRAN/CARVING-HANDOFF.md sec 3a.

A level-14 monitor call served directly by the Resident PIT (S3RPIT). It is not listed in the SINTRAN III Monitor Calls manual: only the dispatch and the handler entry code are recovered from real SINTRAN L bytes; the high-level purpose is unknown.

Status: dispatch byte-proven (GOTAB[15B] = 120501B, live-matched); the F1615 entry stub and the shared S3RPIT workers it calls are real SINTRAN L bytes in the same segment; the call's meaning and one runtime-populated exit are UNVERIFIED (see Honest caveats). All addresses/values are octal.

Dispatch path

flowchart LR
    A["User program<br/>MON 15B"] --> B["ENT14 level-14<br/>T = MON number"]
    B --> C["GOTAB[15B] = 120501B<br/>(byte + live proven)"]
    C --> D["F1615 entry stub<br/>025-S3IRPIT :120501B"]
    D --> E["shared S3RPIT workers<br/>via JPL I : 116234B / 116665B / 116036B"]
    D -.runtime JMP I -31.-> F["ptr@120461B = 000000B<br/>(runtime-populated; unresolved)"]
    class A blue
    class B,C teal
    class D,E green
    class F blue
    classDef blue fill:#E3F2FD,stroke:#0D47A1,color:#0D47A1
    classDef teal fill:#E0F7FA,stroke:#00838F,color:#00838F
    classDef green fill:#E8F5E9,stroke:#2E7D32,color:#2E7D32

The main dispatch (C -> D -> E) is fully carved and statically followable inside 025-S3IRPIT. The dashed hop (D -> F) is the JMP I -31 skip-path exit: its pointer word @120461B reads 000000B in the static image, so it is runtime-populated and cannot be followed from the bytes alone.

Code location (dispatch path)

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

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[15] dispatch word commoncode.asm · .hex 071250B (1 word) 58704 GOTAB+15 = 120501B VERIFIED
F1615 entry stub 025-S3IRPIT.asm · .hex 120501B-120525B (21 words) 55938 F1615 VERIFIED
worker B (via JPL I 35, ptr@120536=116234B) 025-S3IRPIT.asm · .hex 116234B 53560 S3RPIT worker real bytes; extent UNVERIFIED
worker C (via JPL I 33, ptr@120540=116665B) 025-S3IRPIT.asm · .hex 116665B 54122 S3RPIT worker real bytes; extent UNVERIFIED
worker D (via JPL I 23, ptr@120541=116036B) 025-S3IRPIT.asm · .hex 116036B 53308 S3RPIT worker real bytes; extent UNVERIFIED
data word (via LDX I 34/30, ptr@120537=061157B) 025-S3IRPIT.asm · .hex 061157B 23774 S3RPIT data VERIFIED (pointer read)
JMP I -31 exit (ptr@120461B = 000000B) - (runtime-populated) 120461B -> 000000B 39392 runtime-linked UNVERIFIED

Verify by hand (GOTAB word): grep -E '^71250 ' ../../segments-ref/SINTRAN-DATA_commoncode/SINTRAN-DATA_commoncode.hex -> 71250 120501 241 101 58704; then dd if=../../../resident/SINTRAN-DATA_commoncode.bin bs=1 skip=58704 count=2 | od -An -tx1 -> a1 41 (= octal 120501, the F1615 address).

Verify by hand (F1615 stub): grep -E '^120501 ' ../../segments-ref/025-S3IRPIT/025-S3IRPIT.hex -> byte offset 55938; then dd if=../../../segments/025-S3IRPIT.bin bs=1 skip=55938 count=4 | od -An -tx1 -> ba 1d a8 09 (= octal 135035 124011 = JPL I 35 / JMP 11, the stub head).

Instruction walkthrough

Full listing: 015B-Undocumented.ASM. Region A is the F1615 stub (the per-MON handler); Region B is the first shared worker it calls (116234B).

The F16xx symbols are a regular table of same-size per-MON entry stubs (F1610..F1627 are each exactly 025B words apart), so F1615 @120501B is the level-14 stub for MON 15B, not a coincidence. The stub reads X and A, tests T, calls shared workers, and offers a skip-return to the caller - consistent with a small argument-driven monitor call.

  1. Entry / worker call (120501-120502). 120501 JPL I 35 calls shared worker B at 116234B (pointer word @120536). The worker uses a skip / no-skip convention: 120502 JMP 11 -> 120513 is the normal (no-skip) return; straight-line code at 120503 is the skip return.
  2. Skip path (120503-120512). Loads X from data word 061157B (LDX I 34) and A from mem[X-17], calls a second worker C at 116665B (120505 JPL I 33), reloads X (LDX I 30), loads A from 120457B (which reads 000000B), copies A->B (RADD CLD SA DB) and exits via 120512 JMP I -31 through pointer word @120461B - which reads 000000B (see caveats).
  3. Normal path (120513-120525). Subfunction-style dispatch: sets T (SAT 2, then SAT 1), compares the double accumulator against S:T (SKP IF DA EQL ST), and branches - calling a third worker D at 116036B (120516 JPL I 23) on one selector, and bit-testing (120524 BSKP ONE SSK) on another, converging on shared tails at 120534B / 120477B.

Pointer / data words the stub dereferences (data, rendered by nd100-dis as FDV/ADD/STZ; the raw octal is the target): @120536=116234 @120537=061157 @120540=116665 @120541=116036 @120461=000000 @120457=000000.

Parameter / register contract

Reg / field Dir Meaning Verdict
X (ZXREG) in Stub loads/uses X (LDX I 34, LDX I 30, LDA ,X -17) as a pointer/index into a table or descriptor. VERIFIED (bytes)
A (ZAREG) in Stub loads A and compares it (SKP IF DA EQL ST) - an argument/selector value. VERIFIED (bytes)
T (ZTREG) in Selector set/tested (SAT 1, SAT 2, ... EQL ST) - subfunction number. VERIFIED (bytes)
skip return out Worker 116234B returns skip/no-skip; the stub has both paths (JMP 11 vs fall-through). VERIFIED (bytes)
error codes out No explicit error-code load is identifiable in the stub; any status is produced inside the uncarved workers. UNVERIFIED
purpose - The manual does not list MON 15B; the functional meaning of the inputs/outputs is unknown. UNVERIFIED

The exact caller-visible contract is undocumented. What the code proves is only the register usage pattern above.

Pseudo-code (for an emulator)

See 015B-Undocumented.pseudo.c - a pseudo-C model of the F1615 handler for emulator authors. The control flow and the skip / no-skip fork are byte-verified; the semantics of the three shared workers and the runtime JMP I -31 exit are inferred / unresolved, not byte-proven.

Every instruction in the .pseudo.c is translated against the canonical ND100-INSTRUCTION-SEMANTICS.md (SKP IF DA EQL ST compares the single registers A and T - "DA"/"ST" are dst-A/src-T, not a D:A/S:T pair; skip-on-condition skips the next word, do not invert; RADD CLD SA DB = B = A).

Honest caveats

What is byte-proven: GOTAB[15B] = 120501B (raw bytes a1 41 at file offset 0xe550 of SINTRAN-DATA_commoncode.bin, i.e. word 071233B + 015), matching a live-DAP read of the running L system - this is a DIRECT dispatch, not MFELL/000000/fall-through. The earlier NPL-based "GOTAB[15B]=MFELL, handler NOT LOCATED" conclusion is corrected. The F1615 stub at 120501B is coherent real code (not zeros/data), and the three shared workers it reaches (116234B, 116665B, 116036B) plus the data word (061157B) are non-zero, statically followable, coherent S3RPIT code in the same 025-S3IRPIT overlay.

What is NOT proven: 1. Purpose. MON 15B is undocumented. Whether it is a live call or a dormant TSS carryover cannot be decided from the bytes. 2. The JMP I -31 skip-path exit. Pointer word @120461B reads 000000B in the static image - a literal indirect jump to address 0 is nonsensical, so this word is almost certainly patched at runtime (self-modified S3RPIT dispatch). It cannot be resolved from the static image; a live trace is required. 3. Worker extents. 116234B / 116665B / 116036B are shared workers entered by many stubs; they have no bounding symbol and multiple return paths, so their full extent is UNVERIFIED. The .ASM lists worker B (116234B) from entry through its first two return sites for orientation only.

An earlier draft (DISPATCH.md) tabulated 120502 JMP 11 -> 120514B and a few other targets that disagreed with the disassembler; the byte-honest nd100-dis output (used here and in the .ASM) gives JMP 11 -> 120513B. The listing in this folder is the reconciled, byte-true one.

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md §7.6/7.7/8 · dispatch reality: ../../TASK-05-mismatches.md · master map: ../../MON-CALL-INDEX.md.