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MON 311B (octal) - WriteDirEntry (WDIEN)

Changes the information about a directory - the complete contents of a 48-byte directory entry are written. The caller passes the directory index and the directory-entry buffer. The directory must be entered and reserved, and only user SYSTEM may issue the call. ND-100 call.

Status: byte-verified (dispatch + worker body). The worker is real carved code in 006-S3FS. All addresses/values are octal.

CORRECTED 2026-07-13. The previous version of this folder said the call was misattributed (stub-routed), claiming GOTAB[311B] = 112030B routed to a DIA2 level-14 stub in 025-S3IRPIT. That was an artefact of the wrong dispatch model. MON calls take their worker from MCTAB @ 005620B (segment 044-S3IDPIT), not from that GOTAB (which is MFELL for 224 of 256 calls). MCTAB[311B] = 107106B = WDIEN (byte-proven), carved in 006-S3FS - a mode-selecting entry (SSM=1) that joins a body shared with GDIEN and GNAEN. See ../317B-ExecuteCommand/README.md and SINTRAN/CARVING-HANDOFF.md section 3a.

Dispatch path

flowchart LR
    A["User program<br/>MON 311B"] --> B["ENT14 level-14 entry<br/>026-S3IMPIT :072167B"]
    B --> C["GOTAB[311B] = MFELL<br/>MGOTA=071233B :071544B"]
    C --> D["MFELL level switch<br/>026-S3IMPIT :072114B -> CALLP 032201B"]
    D --> E["MCTAB[311B] = WDIEN<br/>MCTAB=005620B :006131B = 107106B"]
    E --> F["WDIEN worker<br/>006-S3FS :107106B"]
    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

There is no dashed hop. GOTAB[311B] = MFELL (byte-proven, 74 4c); MFELL is a program-level switch, not a subroutine call. The monitor level then indexes MCTAB and reaches WDIEN.

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
GOTAB[311B] slot 026-S3IMPIT.asm 071544B = 072114B 32456 -> MFELL VERIFIED
MCTAB[311B] slot 044-S3IDPIT.asm 006131B = 107106B 2226 -> WDIEN VERIFIED
WDIEN worker body 006-S3FS.asm 107106B-107137B+ 50316 WDIEN VERIFIED

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

dd if=026-S3IMPIT.bin bs=1 skip=32456 count=2 | od -An -tx1   ->  74 4c   (= 072114B = MFELL)
dd if=044-S3IDPIT.bin bs=1 skip=2226  count=2 | od -An -tx1   ->  8e 46   (= 107106B = WDIEN)
dd if=006-S3FS.bin    bs=1 skip=50316 count=2 | od -An -tx1   ->  f8 b8   (= 174270B, WDIEN entry: BSET ONE SSM)

Instruction walkthrough

Full listing: 311B-WriteDirEntry.ASM.

Mode-select entries (107106B-107115B). Three sibling entries set a pair of mode bits then merge at the shared body 107116B: - WDIEN (107106B, MON 311B write): BSET ONE SSM / BSET ZRO SSK (SSM=1, SSK=0) - GDIEN (107111B): BSET ZRO SSK / BSET ZRO SSM (both 0) - GNAEN (107114B): BSET ONE SSK / BSET ZRO SSM (SSK=1, SSM=0)

The SSM/SSK status bits are latched here and later tested (BSKP ONE SSM at 107123B, BSKP ONE SSK at 107131B) to fork read vs write and name-lookup vs index-lookup behaviour.

Shared prologue (107116B-107122B). STD I 112 / RADD CLD SL DA / RADD CLD SB DD / SAB 106 save the caller's registers and build the frame; JPL I 107 (-> 107231B) calls the shared directory helper.

Mode fork (107123B-107137B). BSKP ONE SSM sets a write flag into ,B 104 (107126B STA ,B 104, else STZ ,B 104); BSKP ONE SSK sets a name-lookup flag into ,B 105. Those two flags then steer the shared directory-entry body (which validates the SYSTEM-user and reserved-directory preconditions and, on the write path, copies the 48-byte entry).

The mode-bit latch, the shared prologue and the two flag forks are byte-proven; the details of the directory-entry copy in the shared body are inferred from the WDIEN/GDIEN/GNAEN family and the manual.

Parameter / register contract

Reg / field Dir Meaning Verdict
directory index in selects the directory entry to write VERIFIED (structure); byte layout inferred (manual)
entry buffer in 48-byte directory-entry contents to write inferred (manual)
SSM bit internal set to 1 by WDIEN -> selects the write path VERIFIED (bytes)
SSK bit internal 0 for WDIEN (index lookup, not name lookup) VERIFIED (bytes)
,B 104 frame write flag derived from SSM VERIFIED (bytes)
,B 105 frame name-lookup flag derived from SSK VERIFIED (bytes)
caller class in only user SYSTEM; directory entered + reserved inferred (manual)

Pseudo-code (for an emulator)

See 311B-WriteDirEntry.pseudo.c - the SSM/SSK mode latch, the shared prologue and the two flag forks are byte-verified; the directory-entry copy in the shared body is inferred.

Honest caveats

What is byte-proven: GOTAB[311B] = MFELL; MCTAB[311B] = 107106B = WDIEN; the WDIEN entry bytes at 107106B in 006-S3FS match the disassembly (174270B = BSET ONE SSM); WDIEN / GDIEN / GNAEN share one body distinguished by the SSM/SSK mode bits; WDIEN selects the write path (SSM=1).

What is NOT proven: the exact layout of the 48-byte directory entry and the internals of the shared directory body (reached by JPL I 107 at 107122B, not carved in this folder), and the SYSTEM-user / reserved-directory precondition checks (from the manual).

Correction to earlier work. The old folder read the disproven GOTAB and reported GOTAB[311B] = 112030B -> DIA2 stub. The byte-proven worker is MCTAB[311B] = WDIEN = 107106B. The DIA2 reading was the wrong-overlay error.

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