MON 60B (octal) - N500M (ND-500 Monitor Function)¶

The primary gateway by which an ND-100 program controls the ND-500 coprocessor. One MON 60B call selects one of ~67 subfunctions - register and memory access, process control, control-store (microcode) operations, memory configuration, histogram/logging and domain management. On entry A points to a parameter list whose first word is the subfunction code.

Status: dispatch + worker byte-verified; ALL 47 subfunction folders carved (COMPLETE 2026-07-15). The worker N500M = 030416B runs in the 5PIT (PIT 5) context, segment 050-S3I5PIT, confirmed by three independent sources (bytes + the L release-doc PIT layout + coherent code). Every distinct 5IFUNC handler body is carved from the authoritative worker source 5P-P2-MON60.NPL into its own 60B-NNB-NAME/ folder (README + .pseudo.c + verbatim .npl), plus the 5NOPAR common path and the error handlers. See CARVE-PROGRESS.md for the full list, and 60B-CROSS-ANALYSIS-caller-vs-worker.md for the reconciliation with the nd-500-mon:prog caller carve (both sides agree on 5IFUNC).

Server side (the 5NOPAR hand-off target) is now carved too: the ND-500 system monitor (FPT2ENTRY -> 5FP2E, segment 030-S3SM5) with its FUNCS dispatch table, 3022 IOX driver, control-store gate, 5MPM message + activation, level-12 return path, and ALL ~60 FUNCS operation bodies lives in ../../ND500-SYSTEM-MONITOR/. The full MON 60B path is now mapped end to end with named routines at every hop. Remaining: per-handler .ASM (needs the bank-2 5IFUNC address).

Disassembly: 60B-N500M.ASM - the N500M dispatcher (050-S3I5PIT).
Canonical bytes: ../../../segments/044-S3IDPIT.bin (MCTAB), ../../../segments/050-S3I5PIT.bin (worker).

Dispatch path¶

flowchart LR
    A["ND-100 program<br/>A -> params; MON 60B<br/>params[0] = subfunction code"] --> B["ENT14 level-14 entry<br/>026-S3IMPIT :072167B"]
    B --> C["GOTAB[60B] = MFELL<br/>:071313B = 072114B"]
    C --> D["MFELL level switch<br/>026-S3IMPIT :072114B"]
    D --> E["CALLP monitor level<br/>:032201B"]
    E --> F["MCTAB[60B] = N500M<br/>MCTAB=005620B :005700B = 030416B"]
    F --> G["N500M worker (5PIT context)<br/>050-S3I5PIT :030416B"]
    G --> H["subfunction dispatch on params[0]<br/>range-check 177B, MPY/ADD jump table"]
    class A blue
    class B,C,D,E,F teal
    class G,H 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

Why the 5PIT overlay is correct (this was the hard part - see Overlay resolution): the L release doc's Page-Index-Table layout maps MON 60 into PIT 5 (5PIT) at page 13 = virtual 26000B, spanning to 40000B. N500M=030416B is in that MON-60 region, and 050-S3I5PIT ("Image of 5PIT segment") loads at 26000B. So the monitor runs MON 60 with the 5PIT mapped, and 030416B in that context is real N500M code.

Code location (dispatch path)¶

Role	Segment	Addr (octal)	Byte offset	Symbol	Verdict
level-14 monitor entry	026-S3IMPIT (base 32000B)	`072167B`	33006	`ENT14`	VERIFIED
GOTAB[60B] slot	026-S3IMPIT	`071313B` = `072114B`	32548	-> `MFELL`	VERIFIED
MFELL level switch	026-S3IMPIT	`072114B`	32920	`MFELL`	VERIFIED
CALLP	026-S3IMPIT	`032201B`	-	`CALLP`	VERIFIED (entry)
MCTAB[60B] slot	044-S3IDPIT (base 4000B)	`005700B` = `030416B`	1920	-> `N500M`	VERIFIED
N500M worker entry (5PIT)	050-S3I5PIT (base 026000B)	`030416B`	2588	`N500M`	VERIFIED (bytes + release-doc PIT map)

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

dd if=044-S3IDPIT.bin bs=1 skip=1920 count=2 | od -An -tx1   ->  31 0e   (= 030416B = N500M)
dd if=050-S3I5PIT.bin  bs=1 skip=2588 count=2 | od -An -tx1   ->  5a 5f   (= 135137B, N500M first word JPL I 137)
dd if=026-S3IMPIT.bin  bs=1 skip=32548 count=2 | od -An -tx1  ->  74 4c   (= 072114B = MFELL)

Instruction walkthrough¶

Full listing: 60B-N500M.ASM.

Entry (030416B). JPL I 137 calls a common prologue; LDX ,B 20 loads the caller's parameter pointer from the frame; LDA I ,X 132 fetches params[0] (the subfunction code) through the alternate page mapping (BSET ZRO/ONE SSPTM). SAT 177 ; SKP IF DT MGRE SX range-checks the code to 177B and branches to the error path if out of range.

Dispatch. The routine classifies the code through SAT <code> ; SKP IF DA/DX UEQ ST compares (byte-visible: 40B, 15B, 61B, 145B, 16B, ...) and at 030544B computes a jump-table index (LDA I 33 ; MPY 33 ; ADD 33 ; RADD CLD SA DX ; LDA ,X 1). Per-subfunction handlers are being mapped (see below).

Subfunction dispatch - byte analysis¶

RESOLVED: the jump table is 5IFUNC. Full authoritative map (128 entries, code -> handler, cross-verified 3 ways): 60B-5IFUNC-dispatch-table.md. Source: SINTRAN/NPL-SOURCE/NPL/5P-P2-MON60.NPL (the MON 60 worker's own NPL). The NPL dispatch A := 5IFUNC(X) ; A =: P matches the L07 bytes at 030416B, and the L07 SAT 145B boundary compare matches 5IFUNC's valid/ILLFUNC transition at 145B->146B. The caller-side byte-proven codes (37B ICSLOAD, 103B IRSYSP, 133B ILI5EXQ, ...) also match.

Documented user-facing names (7 categories, 0B-142B): 60B-SUBFUNCTIONS-documented.md (from manual ND-60.136.04A).

VERIFIED from the dispatcher bytes: - Range check accepts params[0] up to 177B (SAT 177 ; SKP IF DT MGRE SX at 030421B-030422B); out-of-range -> error path. - The dispatcher's category-boundary compares match the documented category starts: SAT 15B = Category 2 (Process Mgmt) start; SAT 40B = Category 3 (Memory Mgmt) start; SAT 61B = Category 3 end (61B RESER). This alignment is byte-verified and is strong independent evidence the worker really is N500M and the documented 7-category structure is real. - The jump-table index is entry = MEM[X+1] where X = MEM[<ptr>]*MEM[<n>] + MEM[<base>] (LDA I 33 ; MPY 33 ; ADD 33 at 030544B-030546B).

Open (not yet byte-proven), honest: - The jump-table base/stride operands resolve to words the dispatcher reads at low addresses (~005115B, and a base ~115542B) that live in the common-code overlay mapped in the 5PIT context, NOT inside 050-S3I5PIT (which starts at 26000B). Following the table to each handler therefore needs the common-code overlay under the 5PIT PIT - next step. Do NOT guess the entries. - SAT 145B appears in the dispatcher but 145B is beyond the documented max (142B). Could be an internal limit, an undocumented code, or a B01-vs-L07 version difference - unresolved, flagged.

Per-subfunction folder convention¶

Each carved subfunction lives in 60B-NNB-NAME/ and contains four files: - README.md - dispatch, contract, byte status, emulator relevance. - 60B-NNB-NAME.pseudo.c - emulator model. - 60B-NNB-NAME.npl - verbatim copy of the mapping NPL source from 5P-P2-MON60.NPL (the dispatch context + the 5IFUNC slot + the handler body), as reference. Actual code, no line numbers. - 60B-NNB-NAME.ASM - the L07 disassembly of the handler body, ONCE its bank-2 5IFUNC address is located (pending; see 60B-5IFUNC-dispatch-table.md). Until then the folder is README+pseudo.c+npl.

Exemplar: 60B-037B-ICSLOAD/.

Overlay resolution¶

030416B decodes as three different things depending on the mapped PIT context: an ND-500 disk/paging data block in the commoncode/normal overlay (SYMBOL-2-LIST field names N500M, CMD, NSECT, DSKAD, MPAGS, PGCOP, PAGTA, SECTA); ASCII in 003-S3CP; and code in 050-S3I5PIT/046-S3S5PIT. Static symbol matching alone is ambiguous (and 050's carver-assigned N500-SYMBOLS has no N500M - that assignment is "medium confidence" and wrong). The tie-breaker is the L release-doc PIT layout (ND-860230-6-EN ... L-Version.md section 8.2): PIT 5 (5PIT) maps MON 60 at pages 13-17 = 26000B-37777B, which contains 030416B. That is authoritative for which overlay executes.

Honest caveats¶

Byte-verified: the dispatch chain and the worker location/entry (backed by the release-doc PIT map). Not yet proven: the mapping from each subfunction code to its handler, and the names in the documented ~67-function table (Developer/MON/calls/60B_N500M.yaml, 60B_N500M_Functions.md - treat as documented until matched to the byte-verified compare constants). The behavioural contract (error codes, privilege, 5MPM/driver interaction) is from the manual, not these bytes. Per-subfunction folders (60B-NN-Name/) will be added as handlers are traced.

Method: ../../../../../EXTRACTING-RESIDENT-CODE.md · master map: ../../MON-CALL-INDEX.md · ND-500 status: ../../../../../../SINTRAN/ND500/ND500-STATUS-AND-INDEX.md.