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MON 260B (octal) - USCNT (UserControl)

Set user control of a device (manual short name USCNT). The manual lists this call name-only, so the full parameter/return contract is inferred; the carved worker itself is byte-verified.

Status: byte-verified (dispatch + worker body). The worker is real carved code in 003-S3CP, heading a user/system-accounting family USCNT / SYCNT / NRETM / NCHBU. All addresses/values are octal.

CORRECTED 2026-07-13. The previous version of this folder called this call misattributed with a GOTAB "fall-through" and no analysable body. That was an artefact of the wrong dispatch model. MON calls are not dispatched through the level-14 GOTAB (it is MFELL for 224 of 256 calls); they go through MCTAB @ 005620B (segment 044-S3IDPIT). MCTAB[260B] = 047120B = USCNT, and that worker IS carved - in 003-S3CP. See ../317B-ExecuteCommand/README.md and SINTRAN/CARVING-HANDOFF.md section 3a.

Dispatch path

flowchart LR
    A["User program<br/>MON 260B"] --> B["ENT14 level-14<br/>026-S3IMPIT :072167B"]
    B --> C["GOTAB[260B] = MFELL<br/>:071513B"]
    C --> D["MFELL level switch<br/>:072114B -> CALLP 032201B"]
    D --> E["MCTAB[260B] = USCNT<br/>044-S3IDPIT :006100B = 047120B"]
    E --> F["USCNT worker<br/>003-S3CP :047120B"]
    class A blue
    class B,C,D,E teal
    class 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

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[260B] slot 044-S3IDPIT.asm 006100B = 047120B 2176 -> USCNT VERIFIED
USCNT worker body 003-S3CP.asm 047120B-047166B 15520 USCNT VERIFIED

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

dd if=044-S3IDPIT.bin bs=1 skip=2176  count=2 | od -An -tx1   ->  4e 50   (= 047120B = USCNT)
dd if=003-S3CP.bin    bs=1 skip=15520 count=2 | od -An -tx1   ->  45 4d   (= 042515B, USCNT entry)

Instruction walkthrough

Full listing: 260B-UserControl.ASM.

USCNT opens by incrementing a per-user counter (MIN ,X ,B 115) and copying a paired accounting word. The SYCNT/NRETM block (047125B-047146B) updates the matching system-side counters and re-stages several accounting words; one branch reaches MON 0 (ExitFromProgram) at 047147B. The NCHBU tail (047156B-047166B) updates the remaining counters and stores the results. The counter-update structure and the MON 0 branch are byte-proven; which counter corresponds to which resource is inferred.

Parameter / register contract

Reg / field Dir Meaning Verdict
X in base of the per-user accounting block being updated VERIFIED (bytes: MIN ,X ...)
per-user counter ,X 115 etc. in/out incremented / reconciled accounting counters VERIFIED (bytes); semantics inferred
MON 0 branch out one path terminates the program (ExitFromProgram) VERIFIED (bytes)
device / control parameters in manual "set user control of a device" inferred (manual, name-only)

Pseudo-code (for an emulator)

See 260B-UserControl.pseudo.c - the counter-increment structure and the MON 0 branch are byte-verified; the resource/parameter meaning is inferred (the manual documents this call name-only).

Honest caveats

What is byte-proven: MCTAB[260B] = 047120B = USCNT; the USCNT entry bytes at 047120B in 003-S3CP match the disassembly; the routine heads a coherent user/system-accounting family (USCNT/SYCNT/NRETM/NCHBU) that updates per-user and per-system counters and can terminate the program via MON 0 on one branch.

What is NOT proven: the manual documents UserControl name-only, so the exact parameters and which counter maps to which device/resource are inferred. The old misattributed/fall-through verdict was the wrong dispatch model and is withdrawn.

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md · master map: ../../MON-CALL-INDEX.md.