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MON 503B (octal) - InputString (NINST / XNINS)

Reads a line of input into the calling ND-500 process and returns the number of bytes actually read - the input-only counterpart of the fused terminal output+input call 511B-DVIO (whose input phase, XNINSTR, is this call's body). NPL name DVINST; ND-500 System-Monitor GOSW handler name NINSTR. All addresses/values are octal.

Status: handler identity byte-proven (real SINTRAN L bytes at NINST=141272B, extended worker XNINS=141277B; every indirect worker pointer resolves to a named resident). The MON 503B -> NINSTR dispatch crosses an uncarved level-12 GOSW table, so that one link stays UNVERIFIED (see Honest caveats).

Dispatch path

MON 503B is an ND-500 level-12 monitor call. It is not dispatched through the ND-100 monitor GOTAB - a GOTAB[503] probe is meaningless (prove-mon.py 503 reports "500-523B -> level-12 5CMNO GOSW; GOTAB[503] is meaningless"). It arrives at the handler via the resident level-12 GOSW, slot 3 (NINSTR).

flowchart TD
    A["ND-500 process<br/>MON 503B"] --> B["stop MOCALL, level-12"]
    B --> C["MCHANDEL reads<br/>MCNO = 503B"]
    C -.uncarved level-12 GOSW.-> E["5CMNO / L12MIN GOSW<br/>slot 3 = NINSTR"]
    E --> F["NINST/XNINS handler body<br/>026-S3IMPIT :141272B"]
    F --> G["exit: EMONICO / XACTRDY<br/>or NXTMSG (135067B)"]
    class A blue
    class B,C,E teal
    class F,G 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

The dashed hop (C -> E) is the resident level-12 GOSW (5CMNO-L12MIN, slot 3) - it is not present in any carved segment, so it is the one link that cannot be followed statically. The GOSW-slot-3 -> NINSTR mapping is VERIFIED from NPL (MP-P2-N500.NPL lines 1385-1389: STAPROC, NSTOPROC, SWITPROC, NINSTR, ...); the runtime dispatch remains UNVERIFIED because the GOSW overlay is uncarved.

Code location (dispatch path)

Every row is a real region you can open. Byte offset = (addr - loadbase) in octal words x 2 (decimal). Handler load base = 32000B.

Role Segment (full disasm) Addr range (octal) Byte offset Symbol Verdict
GOTAB[503] probe — (ND-500 call, not GOTAB-dispatched) — — (none) MISATTRIBUTED - prove-mon.py 503 reports GOTAB[503] meaningless
Level-12 GOSW dispatch — (uncarved resident level-12) MCHANDEL reads MCNO=503B; 5CMNO-L12MIN slot 3 — 5CMNO / L12MIN -> NINSTR UNVERIFIED - dispatch mechanism, not carved
Level-12 restart tag 026-S3IMPIT.asm · .hex 141266B (1 word) 73068 MO503=141266B VERIFIED (byte; restart tag just before NINST)
Input-string entry 026-S3IMPIT.asm · .hex 141272B 73076 NINST=141272B VERIFIED
Extended worker entry 026-S3IMPIT.asm · .hex 141277B 73086 XNINS=141277B VERIFIED
Part-2 continuation (MO600 tag) 026-S3IMPIT.asm · .hex 141565B–141612B 73450 MO600 / PT2OK / PT2AO / ERRFP / PT2YE / PT2ER VERIFIED (byte; internal restart tags, reached by the body's own direct jumps)
Handler body (closure) 026-S3IMPIT.asm · .hex 141272B–141623B (218 words) 73076 NINST .. pool end VERIFIED (self-contained control flow)

Verify by hand: grep '^141272 ' ../../segments-ref/026-S3IMPIT/026-S3IMPIT.hex -> byte offset 73076; then dd if=../../../segments/026-S3IMPIT.bin bs=1 skip=73076 count=8 | od -An -tx1 -> 52 56 5a 56 f7 42 c6 c2 (= octal 051126 055126 173502 143302, the NINST entry LDT I 126 / LDX I 126 / AAX 102 / LDDTX).

Instruction walkthrough

Full listing: 503B-InputString.ASM. The 218-word window is one self-contained routine (control-flow closure confirmed) with two embedded pointer/parameter pools the disassembler mis-renders as instructions: 141420B..141447B and 141613B..141623B are data (indirect-jump targets + parameter words), not executable code.

Indirect worker pointers, resolved against L07 symbols - the identity proof. Each pointer word resolves one-to-one to this call's worker set (the same family as DVIO), confirming the body:

Ptr word Value Symbol (L07, 5-char) Worker
141423 / 141620 023021 EMONI EMONICO - restart ND-500 proc with error
141424 / 141621 145466 XACTR XACTRDY - reactivate ND-500 executor queue
141425 / 141623 135067 NXTMS NXTMSG - handle next ND-500 message (exit)
141426 147440 5GTDF 5GTDF - get terminal datafield
141427 137167 NORMM NORMMC - non-terminal MON fallback
141430 027212 SET12 SET12 - level-12 setup helper (role inferred)
141431 023624 GCPUD GCPUDF - get ND-500 CPU datafield
141613 023670 WN5ST WN5STATUS - write ND-500 process status

Entry / terminal check (141272..141313) - 141272 LDT I 126 / 141273 LDX I 126 load the message-field base/index (indirect through 141420=004654, 141421=011260); 141274..141276 index and fetch a control word. 141277 JAF 4 (this is the XNINS entry) branches on that field. The error branch 141303..141307 loads SAA 174 (error 174) then leaves via EMONICO/XACTRDY/NXTMSG. 141310..141313 store to msg field 136B, then 141312 JPL I -> 5GTDF (get terminal datafield) with 141313 JMP I -> NORMMC as the not-a-terminal skip-return.

Line-status check + setup (141314..141417) - 141314..141317 test a datafield status bit (LDA,X 3 / BSKP ONE); 141320..141321 JMP I -> NORMMC on the not-a-terminal case. 141322..141325 JPL I -> SET12 prepares the level-12 transfer. 141326..141341 range/status-check the request; the error branch builds a code and exits via EMONICO/XACTRDY. 141342..141417 scale field indices and build the input-transfer descriptor (max-bytes and destination-array fields read from the message buffer - layout inferred); the block ends 141417 JMP 31 -> 141450, jumping over the pool at 141420..141447.

Transfer processing part 2a (141450..141564) - a SAT-driven decision ladder (SAT -1 / SAT 11 / SAT 7 / SAT 10, each with SKP IF DA EQL/MLST ST) classifies the current character/state and accumulates the running result in msg field -11B (STA,B -11). 141514 SAA 14 marks the process, JPL I -> WN5STATUS.

Part 2 continuation (141565..141612, MO600 tag) - the finish/echo/error tags PT2OK=141567, PT2AO=141570, ERRFP=141574, PT2YE=141576, PT2ER=141600 finalise the returned byte count (STD into a msg field), and select the exit (JPL I -> EMONICO/XACTRDY on error tags, else JMP I -> NXTMSG via pool word 141623=135067). This block is reached by the body's own direct jumps 141544 -> 141605 and 141562 -> 141571, which is why the closed region extends to 141623 (see caveats).

Parameter / register contract

ND-500 monitor calls pass parameters in the ND-500 message buffer (indexed by 5MBBANK + field displacement), not in ND-100 A/T/X user registers. The register use below is level-12 driver-internal.

Item Dir Meaning Verdict
X / T (entry) in ND-500 message base + field index VERIFIED (bytes: LDT I 126 / LDX I 126 msg indexing)
open / LDN file number (msg) in source file/terminal to read from inferred (reference manual; NPL DVINST - not isolatable in these bytes)
max bytes to read (msg) in destination buffer size / max input length inferred (read in the 141342..141417 setup; exact field UNVERIFIED)
destination array (msg) in where the input line is written inferred (message-buffer layout, not byte-isolated)
returned byte count (msg) out number of bytes actually read inferred (finalised in the part-2 block, written to a msg field)
terminal datafield in fetched via 5GTDF; NORMMC skip if not a terminal VERIFIED (indirect ptr resolves to 5GTDF/NORMMC)
Error 174 (EC174) out illegal parameter -> EMONICO VERIFIED (SAA 174 byte)
Error 316 out terminal line not connected inferred (NPL only; not byte-isolated here)
Error 3 out end-of-file on nowait input inferred (NPL/reference manual only)
Exit out EMONICO/XACTRDY (error restart) or NXTMSG (done) VERIFIED (indirect ptrs resolve)
Skip-return — none in the ND-100 sense; control leaves via the workers above VERIFIED (none in-window)

Pseudo-code (for an emulator)

The pseudo-C is grounded in the ND-100 instruction-semantics reference ../../instruction-semantics/ND100-INSTRUCTION-SEMANTICS.md: the T/X transfers are 24-bit physical accesses EL = ((T & 0377) << 16) | ((X + disp3) & 0177777) (T = the message-buffer bank, MMU-bypassed), and RADD CLD Sx Dy = y = x.

See 503B-InputString.pseudo.c - a pseudo-C model of the input-string worker for emulator authors. Control flow, the eight indirect worker pointers (EMONICO, XACTRDY, NXTMSG, 5GTDF, NORMMC, SET12, GCPUDF, WN5STATUS), and the SAA 174 error path are byte-verified; the byte-count / buffer-copy arithmetic and the message-field layout are inferred from the code structure and the reference manual (a different revision than L). ND-500 parameters are passed in the ND-500 message buffer, not in A/T/X.

Honest caveats

What is byte-proven: the handler at NINST=141272B (with extended entry XNINS=141277B) is real SINTRAN L code carved from 026-S3IMPIT (load 32000B). Two independent anchors agree: (1) NINST=141272 / XNINS=141277 in the L07 symbol table, and (2) every indirect worker pointer resolves to exactly this call's worker set (EMONICO, XACTRDY, NXTMSG, 5GTDF, NORMMC, SET12, GCPUDF, WN5STATUS). The illegal-parameter error path (SAA 174 -> EMONICO) is byte-verified. The carved slice is byte-identical to the canonical segment (dd above reproduces the entry words).

Closure note (why the window is 141272..141623, past MO600=141565). The body's own direct jumps 141544 -> 141605 and 141562 -> 141571 land in the part-2 block that begins at the MO600=141565 tag. MO600 is an internal level-12 restart/continuation tag (analogous to MO503=141266 which sits just before NINST), not a separate handler - the PT2OK/PT2AO/PT2YE/PT2ER/ERRFP symbols are this routine's own finish/error labels. The genuinely next handler, MOVTA/GERRC=141624B (MON 505 GetTrapReason), is excluded. So closing the control flow to 141623 includes this routine's part-2 code plus its trailing pointer pool (141613..141623) without swallowing a foreign routine. validate-mon-carves.py confirms SIZE/CONTIG/CLOSURE with zero direct escapes.

What is NOT proven: - The dispatch. MON 503 is an ND-500 level-12 call; it is not in GOTAB (prove-mon.py 503 reports GOTAB[503] meaningless). The real path is the resident level-12 GOSW (MCHANDEL reads MCNO, 5CMNO-L12MIN slot 3 = NINSTR), which is in an uncarved overlay and cannot be followed statically. The GOSW-slot-3 -> NINSTR mapping is VERIFIED from NPL; the runtime arrival is UNVERIFIED. - The exact parameter fields. The open/file number, max-byte-count and destination-array message fields, and the returned byte-count write-back, are read from the ND-500 message buffer whose exact displacements are not byte-isolated in this window - marked inferred. - The NPL-only errors. 316 (line not connected) and 3 (end-of-file on nowait input) come from the reference manual / NPL DVINST; only the 174 error is byte-proven here. - NPL is a different revision than L. NPL names the routine DVINST/NINSTR; the L bytes place NINST=141272 / XNINS=141277. Only the behaviour and worker names carry over - the worker names were re-verified against the L07 pointer words above.

Confirming the full chain needs a live trace (break at the level-12 GOSW on a real ND-500 MON 503, single-step, confirm P lands on NINST=141272).

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md §7.6/7.7 · dispatch reality: ../../TASK-05-mismatches.md · master map: ../../MON-CALL-INDEX.md.