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MON 500B (octal) — StartProcess (STAPROC)

Starts an ND-500 process identified by a process number plus a magic/reservation word. It shares one code body with SwitchProcess (SWITP) — both enter the same word 140356B — and with the stop/next-process branch (NSTOP at 140511B); the body validates the process number, compares the stored magic word, then dispatches resident ND-500 level-12 scheduler workers.

Status: handler body is real SINTRAN L bytes, symbol-pinned (STAPR=SWITP=140356B); the MON 500B → handler dispatch is an ND-500 level-12 GOSW that no tool here byte-proves, and GOTAB[500] is an unrelated ND-100 slot (see Honest caveats). All addresses/values are octal.

Dispatch path

flowchart TD
    A["ND-500 program<br/>MON 500B"] --> B["stop MOCALL, level-12<br/>MCHANDEL reads MCNO=500B"]
    B -.uncarved GOSW.-> C["5CMNO / L12MIN<br/>GOSW index 0"]
    C --> D["STAPROC / SWITPROC body<br/>026-S3IMPIT :140356B"]
    D --> E["scheduler workers<br/>via JPL I 131/120/110/...<br/>(14054xB, uncarved)"]
    G["GOTAB[500] = 057366B (T102W)<br/>unrelated ND-100 slot"] -. not this call .-> A
    class A blue
    class B,C teal
    class D,E green
    class G 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 dashed hop (B ⇢ C) is the ND-500 level-12 GOSW branch — not byte-proven by any tool here. GOTAB[500] is shown only to say plainly that it is not the StartProcess handler.

Code location (dispatch path)

Every row that is carved is a real region you can open. Byte offset = (addr − loadbase) in octal words × 2.

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[500] slot (NOT this call) commoncode.asm · .hex 071733B (1 word) 59318 GOTAB+500 = 057366B (T102W) MISATTRIBUTED — unrelated ND-100 handler; ND-500 calls are not GOTAB-dispatched
Level-12 GOSW dispatch — (uncarved) — — 5CMNO / L12MIN GOSW idx 0 UNVERIFIED — no tool byte-proves the GOSW word
STAPROC / SWITPROC body 026-S3IMPIT.asm · .hex 140356B–140515B (96w) 72156 STAPR=SWITP=140356B; NSTOP=140511B VERIFIED — symbol-pinned; bytes match canonical
Shared scheduler / return workers 026-S3IMPIT.asm (targets past body) ~140543B–140560B not carved JPL I 131/120/110/107/106/101/102/66/76/62/44/35 UNVERIFIED — worker bodies not carved

Verify by hand: grep '^140356 ' ../../segments-ref/026-S3IMPIT/026-S3IMPIT.hex → byte offset 72156; then dd if=../../../segments/026-S3IMPIT.bin bs=1 skip=72156 count=8 | od -An -tx1 → 52 6e f7 40 c6 c2 52 6c (= octal 051156 173500 143302 051154 …, the STAPR entry). Symbols: grep -iE 'STAPR|SWITP|NSTOP' ../../segments-ref/026-S3IMPIT/026-S3IMPIT.symbols.txt.

Instruction walkthrough

Full listing: 500B-StartProcess.ASM. I nn = indirect through the pointer word at frame offset nn; those pointer words live just past the code (targets like 140543B) and are the shared-worker entry addresses.

Entry prologue + bounds check (140356–140366) — LDT I 156 / AAX 100 / LDDTX fetch the descriptor-table limit pair; SKP IF DT LST SA and SKP IF DT MGRE SA are a two-sided range test on the caller's process number. Failing either side does JMP 17 → 140405 (return/error block).

Index + magic compare (140367–140404) — SUB I 146 normalises the number, MPY 147 / ADD 147 scale it by descriptor size; the code follows into the descriptor, loads the stored magic/reservation word, and SKP IF DA EQL SD compares it. A mismatch (JMP 3 → 140405) is the classic "illegal process" rejection (EILPROC-style). LDA ,X 1 then loads the state field; JAF 6 → 140412 takes the active-process path if it is non-zero.

Return / error block (140405–140411) — three consecutive indirect entries through pointer 134 (JPL I 134 → 140543/140544, JMP I 134 → 140545) implement the multi-way (normal / skip / error) return convention: the pointed worker sets status and performs the MON skip-return.

Active-process main path (140412–140455) — inspects a descriptor bit (BSKP ONE 60 DD), dispatches on a mode selector (SAT 13 vs SAT 16 — meaning inferred), and calls a chain of resident scheduler workers via pointer words 131/120/110/107/106/101/102. SAA 1 before the 102 calls looks like a "start" flag. RAND 0 0 words are alignment/no-op fill between call clusters.

Alternate / NSTOP tail path (140456–140515) — BSET ONE 170 DA sets a status bit; NSTOP (140511B) is the stop / next-process branch that shares this body. The carve deliberately extends through it so every direct branch resolves inside the file; the window ends at 140515B, one word before the next named symbol SBTPH=140515B.

Parameter / register contract

Reg / field Dir Meaning Verdict
ND-500 process number in caller's process id in A; range-checked at 140356–140366 VERIFIED (bounds test in bytes)
Magic / reservation word in compared with stored descriptor word at 140400–140402 VERIFIED (compare + reject branch)
A (entry) in carries the process number into the bounds/index math (LDDTX/SUB/MPY) VERIFIED (bytes)
Mode selector (13 / 16) internal selects start vs switch behaviour at 140420–140425 inferred (numeric constants; meaning not proven)
Status / result out set by the shared return workers via pointer 134 / 35 worker call VERIFIED; exact code inferred (bodies uncarved)
Skip return out multi-way return through pointer-134/pointer-35 workers VERIFIED (JPL I / JMP I return funnel)
Error (illegal process) out magic-mismatch / out-of-range → return block 140405B path VERIFIED; exact error code (EILPROC?) set in an uncarved worker — inferred

The ND-500 message-buffer field names (NPROC, Status, EILPROC, OKMONICO) are behaviour hints from the NPL source revision, not proven from these L bytes. The bytes prove the shape (bounds check, magic compare, worker dispatch, skip-return); the field offsets and error-code constants live in workers this file does not contain.

Pseudo-code (for an emulator)

See 500B-StartProcess.pseudo.c — a pseudo-C model of the handler for emulator authors. Control flow (bounds check → index → magic compare → state fork → worker dispatch → skip-return) is byte-verified; the shared-worker semantics and the meaning of mode selectors 13/16 are inferred from the call structure.

Every instruction is modelled against the canonical ../../instruction-semantics/ND100-INSTRUCTION-SEMANTICS.md. The LDDTX/LDATX/LDXTX/STATX operations are T/X physical (bank) transfers: they read and write the ND-500 message buffer at a 24-bit PHYSICAL address EL = ((T & 0377) << 16) | (X & 0177777) that BYPASSES the MMU (section 5). T holds the message-buffer bank, so the process number and its descriptor words are read FROM the message buffer via phys[ELADDR(T,X)], not from ND-100 registers.

Honest caveats

What is byte-proven: the 96 carved words are real SINTRAN L bytes; the local .bin and .ASM agree word-for-word and match the canonical 026-S3IMPIT.bin at byte offset 72156 (first word 051156B). The L07 symbol table pins STAPR=140356B, SWITP=140356B, NSTOP=140511B to this exact window, so the handler identity is symbol-verified, and every direct branch resolves inside 140356B–140515B (control-flow complete).

What is NOT proven — the dispatch bridge. prove-mon.py 500 reads GOTAB (the ordinary ND-100 MON dispatch table) and reports GOTAB[500] = 057366B → T102W. That is a different, unrelated ND-100 handler that merely occupies slot 500; MON 500B is an ND-500 level-12 GOSW call (5CMNO/L12MIN, GOSW index 0) and is not dispatched through GOTAB. No tool here byte-proves the GOSW dispatch word, so the MON 500B → STAPROC link rests on the L07 symbol table + the carved bytes, not a followed pointer. Confirming it needs a live trace (break on the level-12 ND-500 command handler for MCNO=500B, single-step the GOSW, confirm P lands on STAPR=140356B).

Worker bodies are outside this file. All the deeper semantics — start vs switch vs stop, exact status/error codes, the meaning of mode selectors 13/16 — live in the shared workers reached by JPL I 131/120/110/107/106/101/102/66/76/62/44/35 (pointer targets 14054xB–14056xB), which are not in this carve. This reconciles the two prior notes into one story: the body is proven, the entry into it and its called workers are not.

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