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MON 3B (octal) - ECHOM

Short name ECHOM. The old folder glossed MON 3B as "SetEcho"; the carved worker is a page-table-crossing block-copy routine, so the exact function is left inferred (see caveats).

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

OVERLAY RESOLVED 2026-07-13. An intermediate pass could not read a coherent body: at 044540B the 003-S3CP overlay holds ASCII command-name text, not code. Wrong overlay. The real ECHOM worker is in the monitor-PIT overlay 026-S3IMPIT (identical in 017-S3SMPIT), confirmed by its MOVEW block copies bracketed by BSET ONE/ZRO SSPTM (the cross-page-table switch) - monitor-level machinery that belongs in the monitor-PIT view. 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 3B"] --> B["ENT14 level-14<br/>026-S3IMPIT :072167B"]
    B --> C["GOTAB[3B] = MFELL<br/>:071236B"]
    C --> D["MFELL level switch<br/>:072114B -> CALLP 032201B"]
    D --> E["MCTAB[3B] = ECHOM<br/>044-S3IDPIT :005623B = 044540B"]
    E --> F["ECHOM worker<br/>026-S3IMPIT :044540B"]
    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[3B] slot 044-S3IDPIT.asm 005623B = 044540B 1830 -> ECHOM VERIFIED
ECHOM worker body 026-S3IMPIT.asm 044540B-044610B 10944 ECHOM VERIFIED (code); overlay inferred

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

dd if=044-S3IDPIT.bin bs=1 skip=1830  count=2 | od -An -tx1   ->  49 60   (= 044540B = ECHOM)
dd if=026-S3IMPIT.bin bs=1 skip=10944 count=2 | od -An -tx1   ->  59 2a   (= 054452B, ECHOM entry LDX ,B 52)

Instruction walkthrough

Full listing: 3B-SetEcho.ASM.

The worker performs three MOVEW block moves (044545B, 044561B, 044576B) between frame-relative descriptors, computing source/size operands from frame slots 52/53/62/64 and calling helpers via JPL I 30 / JPL I 11. The second helper call is bracketed by BSET ONE SSPTM ... BSET ZRO SSPTM (044602B / 044605B) - it accesses memory through the alternate page table, i.e. it copies across PIT boundaries. It returns via JMP I -117 (044610B).

What the three blocks are and the exact effect are not decoded here (see caveats).

Parameter / register contract

Reg / field Dir Meaning Verdict
,B 52 in source descriptor for the block moves VERIFIED (bytes)
,B 53 / ,B 62 / ,B 64 in size / helper operands VERIFIED (bytes); meaning inferred
MOVEW x3 internal three block copies, one across the alternate page table (SSPTM) VERIFIED (bytes)
return out via JMP I -117 (-> 044471B) VERIFIED (bytes)
function - manual gloss "SetEcho"; carved code is block-copy, not an echo-mode flag INFERRED / unresolved

Pseudo-code (for an emulator)

See 3B-SetEcho.pseudo.c - the block-move control flow and the page-table switch are byte-verified; the semantic purpose is inferred.

Honest caveats

What is byte-proven: MCTAB[3B] = 044540B = ECHOM; the worker at 044540B in 026-S3IMPIT is a coherent routine doing three MOVEW block copies, one across the alternate page table, then returning.

What is NOT proven: (1) that 026-S3IMPIT vs its byte-identical swap twin 017-S3SMPIT is the exact mapped overlay - indistinguishable by bytes; the choice rests on coherent code + monitor-PIT architecture, not a followed pointer. (2) That this routine is "SetEcho" - the carved body is a block-copy, which does not match a terminal-echo-flag primitive; the name-to-function mapping is unresolved and may need the manual entry for MON 3B or a live trace. The 003-S3CP reading (ASCII text) is definitively the WRONG overlay and is retired.

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