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MON 104B (octal) - HOLD (SuspendProgram)

Suspend the calling program / yield the CPU at a chosen priority. Short name HOLD.

Status: byte-verified dispatch + worker body. Worker is coherent code in 026-S3IMPIT (the monitor-PIT overlay). All addresses/values octal.

OVERLAY RESOLVED 2026-07-13. An intermediate pass flagged this worker as "a data table, not code". That was an overlay error: at 040645B the 003-S3CP overlay holds a powers-of-ten CONSTANT table (100000000, 10^7 .. 10^0), used by the neighbouring clock/decimal code. The real HOLD worker is in the monitor-PIT overlay 026-S3IMPIT (identical in 017-S3SMPIT) - the view the monitor level actually runs in, since CALLP dispatches there. See SINTRAN/CARVING-HANDOFF.md section 3a and the overlay trap in the sintran-carving skill.

Dispatch path

flowchart LR
    A["User program<br/>MON 104B"] --> B["ENT14 level-14<br/>026-S3IMPIT :072167B"]
    B --> C["GOTAB[104B] = MFELL<br/>:071543B"]
    C --> D["MFELL level switch<br/>:072114B -> CALLP 032201B"]
    D --> E["MCTAB[104B] = HOLD<br/>044-S3IDPIT :005724B = 040645B"]
    E --> F["HOLD worker<br/>026-S3IMPIT :040645B"]
    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); reproduced with dd.

Role Segment Addr (octal) Byte offset Symbol Verdict
MCTAB[104B] slot 044-S3IDPIT.asm 005724B = 040645B 1960 -> HOLD VERIFIED
HOLD worker body 026-S3IMPIT.asm 040645B-040663B 6986 HOLD VERIFIED (code); overlay inferred

Verify by hand (from ...\versions\L-VSX-500\segments\): 

dd if=044-S3IDPIT.bin bs=1 skip=1960 count=2 | od -An -tx1   ->  41 a5   (= 040645B = HOLD)
dd if=026-S3IMPIT.bin bs=1 skip=6986 count=2 | od -An -tx1   ->  48 11   (= 044021B, HOLD entry LDA 21)

Instruction walkthrough

Full listing: 104B-SuspendProgram.ASM.

The worker is a 5-way priority-ladder (040645B-040655B): five entry points, each loading a different priority level into A (21B / 20B / 17B / 16B / 15B), all jumping to a common tail at 040656B. The tail (040656B-040663B) sets B and L from a saved value (LDT -115 / RADD CLD ST DB / RADD CLD ST DL), enables interrupts (ION), and EXITs - i.e. it returns control to the scheduler at the chosen priority. This is the classic shape of a suspend/yield primitive.

Parameter / register contract

Reg / field Dir Meaning Verdict
entry point in selects the priority level (21B..15B) at which to suspend VERIFIED (bytes)
A internal holds the selected priority, staged for the tail VERIFIED (bytes)
T (,B -115) internal saved base/link value restored into B and L VERIFIED (bytes)
return out via ION + EXIT (to the scheduler) VERIFIED (bytes)

The mapping from the caller's MON-104B arguments to the specific priority entry point is inferred (it is set by the level switch / caller wrapper, not visible in this body).

Pseudo-code (for an emulator)

See 104B-SuspendProgram.pseudo.c - the priority-ladder and the ION/EXIT tail are byte-verified; the argument-to-priority mapping is inferred.

Honest caveats

What is byte-proven: MCTAB[104B] = 040645B = HOLD; the worker at 040645B in 026-S3IMPIT is a coherent 5-entry priority ladder ending in ION/EXIT.

What is NOT proven: that 026-S3IMPIT (as opposed to 017-S3SMPIT, its byte-identical swap twin) is the exact overlay the monitor maps for this call - the two are indistinguishable by bytes. The overlay choice rests on "coherent code + the monitor-PIT architecture (CALLP dispatches on this level)", not a followed pointer. The 003-S3CP reading (a powers-of-ten table) is definitively the WRONG overlay and is retired.

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