ND-500 Swapper (5SWAP) - Deep Analysis¶

Corrected 2026-07-08. Earlier versions said the swapper "runs on the ND-500"; that was wrong. 5SWAP is an ND-100 RT-program (5SWRT, RP-P2-N500.NPL:16-58, using 2BANK and MON 131/ABSLI - both ND-100 constructs). What lives on the ND-500 side is process #0* (S500S/5SWPROC), whose message buffer SWMSG carries the swap requests; the ND-100 program serves that process. See ND500-SWAPPER-LOADING-MECHANISM.md and ND500-BUS-INTERFACE-REFERENCE.md section 12.

Purpose¶

Complete analysis of the SINTRAN III swapper subsystem for ND-500. The swapper is an event-driven segment loading and page swapping service - NOT a passive polling mechanism.

Source: MP-P2-N500.NPL (lines 1031-1188, 2851-2908, 2970-3040)

1. What the Swapper Does¶

The swapper subsystem (ND-100 RT-program 5SWAP/5SWRT serving ND-500 **process

0**) handles:¶

Function	Description
Segment allocation	Allocating disk pages for new memory segments
Page swapping	Reading/writing memory pages to/from disk
Disk I/O coordination	Managing disk transfers via queue pool elements (on the ND-100)
ND-500 memory service	Serving page faults and segment loads FOR the ND-500 processes

2. Swapper State Machine¶

2.1 Process States (from perspective of processes using the swapper)¶

Symbol	Value (Oct)	Value (Dec)	Meaning
LSWPWAIT	4	4	Process waiting for swapper (blocked in queue)
LSWPPING	6	6	Process using swapper (request being processed)
LACTIVE	12	10	Process active (has swapper result)

2.2 Swapper Internal States¶

Symbol	Meaning
PSWWAIT	Swapper is idle, waiting for work
SWPPING	Swapper is actively processing a request
PSW1WAIT	Swapper waiting for disk I/O completion

2.3 State Transition Diagram¶

stateDiagram-v2
    [*] --> LACTIVE: Process running
    LACTIVE --> LSWPWAIT: Needs swapper service
    LSWPWAIT --> LSWPPING: Swapper accepts request
    LSWPPING --> LACTIVE: Swapper completes
    LSWPWAIT --> LSWPWAIT: Swapper busy (queued in FIFO)

    note right of LSWPWAIT
        Process blocked
        Inserted in Swap-wait-FIFO
        if swapper busy
    end note

    note right of LSWPPING
        Swapper processing request
        Disk I/O in progress
    end note

3. Complete Request Flow¶

3.1 High-Level Flow¶

flowchart TD
    A[Process needs swapper] --> B[Call 5ACTSWAPPER]
    B --> C{Swapper free?<br/>PSWWAIT}
    C -->|Yes| D[Set LSWPPING state]
    C -->|No| E[Insert in Swap-wait-FIFO]
    D --> F[XACTRDY: Select work]
    F --> G[LOWACT500: Activate ND-500]
    G --> H[ND-500 processes request]
    H --> I{Disk I/O needed?}
    I -->|Yes| J[M5TRANS: Disk transfer]
    I -->|No| K[Direct memory operation]
    J --> L[Wait for disk completion]
    L --> M[SWPD4: Swapper idle]
    K --> M
    M --> N{FIFO has waiting?}
    N -->|Yes| O[Dequeue next request]
    N -->|No| P[Stay idle PSWWAIT]
    O --> D
    E --> Q[Wait in queue]
    Q --> O

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    style G fill:#E91E63,stroke:#C2185B,stroke-width:2px,color:#fff
    style H fill:#9C27B0,stroke:#7B1FA2,stroke-width:2px,color:#fff
    style J fill:#4CAF50,stroke:#388E3C,stroke-width:2px,color:#fff
    style M fill:#009688,stroke:#00796B,stroke-width:2px,color:#fff

3.2 5ACTSWAPPER Subroutine (Lines 2851-2908)¶

This is the key entry point for requesting swapper service.

flowchart TD
    A[5ACTSWAPPER Entry] --> B[Set process to SWPWAIT state]
    B --> C[Read swapper status from SWMSG]
    C --> D{Swapper status = PSWWAIT?}
    D -->|Yes - Swapper free| E[Set swapper to SWPPING]
    D -->|No - Swapper busy| F[Get FIFO pointers from N500DF]
    E --> G[Call XACTRDY]
    G --> H[Call LOWACT500]
    H --> I[Return - request activated]
    F --> J[Calculate FIFO insert position]
    J --> K[Insert message in Swap-wait-FIFO]
    K --> L[Return - request queued]

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    style E fill:#4CAF50,stroke:#388E3C,stroke-width:2px,color:#fff
    style H fill:#E91E63,stroke:#C2185B,stroke-width:2px,color:#fff
    style K fill:#FFA726,stroke:#F57C00,stroke-width:2px,color:#fff

Source (MP-P2-N500.NPL lines 2862-2906):

Line 2862: SWPWAIT; CALL WN5STATUS                    % Mark process waiting
Line 2864: X:=SWMSG; CALL RN5STATUS
Line 2865: IF A=PSWWAIT THEN                          % Swapper free?
Line 2870:    SWPPING; CALL WN5STATUS                 % Mark swapper in use
Line 2871:    X:=SWMSG; CALL XACTRDY                  % Reactivate ND-500
Line 2872:    CALL LOWACT500
Line 2898: ELSE
Line 2899:    T:=5MBBANK; X:="N500DF".X500DF
Line 2900:    *AAX X5MXF; LDATX                       % Get FIFO pointers
Line 2901:    A=:L; *AAX X5SWF-X5MXF; LDDTX
Line 2902:    IF A=:D+1>=L THEN A:=0 FI               % Wrap FIFO
Line 2903:    D SH 1=:L; *AAX X5SWB-X5SWF; LDDTX      % Compute FIFO address
Line 2904:    X:=D+L; T:=A+C; CMSGTOSW; *STDTX        % Insert message
Line 2906: FI

4. FIFO Queue Processing (SWPD4)¶

When the swapper completes a request, it checks the Swap-wait-FIFO for waiting processes.

4.1 SWPD4 Flow Diagram¶

flowchart TD
    A[SWPD4: Swapper request complete] --> B[Set swapper status to PSWWAIT]
    B --> C[Get FIFO read pointer X5SWF]
    C --> D[Get FIFO write pointer X5SWT]
    D --> E{Read = Write?<br/>FIFO empty?}
    E -->|Yes| F[Return - stay idle]
    E -->|No| G[Read message from FIFO]
    G --> H[Increment read pointer]
    H --> I{Pointer >= max?}
    I -->|Yes| J[Wrap pointer to 0]
    I -->|No| K[Continue]
    J --> K
    K --> L[Get waiting process]
    L --> M{Process still in LSWPWAIT?}
    M -->|No - cancelled| C
    M -->|Yes| N[Call 5ACTSWAPPER]
    N --> O[Process request]

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    style F fill:#FFA726,stroke:#F57C00,stroke-width:2px,color:#fff
    style N fill:#4CAF50,stroke:#388E3C,stroke-width:2px,color:#fff

Source (MP-P2-N500.NPL lines 1031-1066):

Line 1031: SWPD4: PSWWAIT; X:=SWMSG; CALL WN5STATUS   % Swapper now idle
Line 1032:        T:=5MBBANK; X:="N500DF".X500DF
Line 1033:        *AAX X5SWF; LDDTX                   % Get FIFO read pointer
Line 1034:        A=:D; *AAX X5SWT-X5SWF; LDATX       % Get FIFO write pointer
Line 1035:        IF A=D GO SWPD5                     % FIFO empty? Exit
Line 1040:        % Dequeue and process waiting request
Line 1050:        IF process still in LSWPWAIT        % Still waiting?
Line 1052:           CALL 5ACTSWAPPER                 % Yes, activate it

5. Work Triggering Mechanisms¶

5.1 What Triggers Actual Work¶

The swapper is event-driven, not polling-based. Work is triggered by:

flowchart LR
    subgraph "Triggers"
        A[Process calls 5ACTSWAPPER]
        B[Timer expires in 500HIST]
        C[Disk I/O completes]
        D[ND-500 interrupt]
    end

    subgraph "Activation Path"
        E[XACTRDY: Select highest priority]
        F[LOWACT500: Hardware activation]
        G[ND-500 CPU wakes up]
    end

    subgraph "Work Execution"
        H[Process swapper message]
        I[Disk I/O if needed]
        J[Return result via 5MPM]
    end

    A --> E
    B --> E
    C --> E
    D --> E
    E --> F
    F --> G
    G --> H
    H --> I
    I --> J

    style F fill:#E91E63,stroke:#C2185B,stroke-width:2px,color:#fff
    style G fill:#9C27B0,stroke:#7B1FA2,stroke-width:2px,color:#fff

5.2 XACTRDY - Priority-Based Work Selection (Lines 2970-3040)¶

flowchart TD
    A[XACTRDY Entry] --> B[Get current ND-500 CPU status]
    B --> C{Swapper message waiting?<br/>A><MSGN500 AND A><WAITING}
    C -->|No| D[Return - nothing to do]
    C -->|Yes| E[Scan all ND-500 CPUs]
    E --> F{CPU alive and no power fail?}
    F -->|No| G[Next CPU]
    F -->|Yes| H[Get maillink from 5MPM]
    H --> I[Check X5CPU status]
    I --> J{MPACTIVE?}
    J -->|No| G
    J -->|Yes| K[Get current process]
    K --> L[Compare priorities]
    L --> M{Higher priority found?}
    M -->|Yes| N[Update selection]
    M -->|No| G
    N --> G
    G --> O{More CPUs?}
    O -->|Yes| E
    O -->|No| P[XKICK500: Activate selected]

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    style P fill:#E91E63,stroke:#C2185B,stroke-width:2px,color:#fff

5.3 LOWACT500 - Physical ND-500 Activation¶

LOWACT500 is the critical hardware activation routine. It sets flags that physically wake up the ND-500 CPU.

Line 245: CPUAVAILABLE BONE LV2ACT=:CPUAVAILABLE
Line 251: CALL LOWACT500
Line 459: CALL LOWACT500; LTTMR=:TMR    % Reactivate ND-500

Action	Effect
Set LV2ACT bit in CPUAVAILABLE	Signal that Level 2 work is ready
Write to hardware registers	Physical wake-up of ND-500
ND-500 exits idle loop	Begins processing messages

6. Swapper Operations¶

6.1 LSWPAGE - Disk I/O (Lines 1070-1114)¶

flowchart TD
    A[LSWPAGE Entry] --> B[Set status PSW1WAIT]
    B --> C[Extract disk parameters from SWMSG]
    C --> D[Get disk unit, function, address, length]
    D --> E[Allocate queue pool element QP5SW]
    E --> F[Set up transfer parameters]
    F --> G[Call M5TRANS - initiate transfer]
    G --> H[Wait for disk completion]
    H --> I{Transfer successful?}
    I -->|Yes| J[Call OKMONICO - success]
    I -->|No| K[Call EMONICO - error 1055]
    J --> L[Call XACT500 - reactivate]
    K --> L
    L --> M[Process next message]

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    style G fill:#4CAF50,stroke:#388E3C,stroke-width:2px,color:#fff
    style J fill:#4CAF50,stroke:#388E3C,stroke-width:2px,color:#fff
    style K fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff

Source (MP-P2-N500.NPL lines 1070-1095):

Line 1070: LSWPAGE:
Line 1071:    X:=SWMSG; PSW1WAIT; CALL WN5STATUS
Line 1072:    T:=5MBBANK; *AAX HSWPI; LDDTX
Line 1080:    % Extract disk parameters
Line 1085:    T:="QP100".QP5SW                    % Swapper queue element
Line 1086:    -1=:X.QP5SW; X:=T                   % "LINK OUT"
Line 1088:    "5SWAP"=:X.RTRES; 0=:X.NLINK        % Mark swapper as owner
Line 1092:    *LDF I (XABSF; STF ABFUN,X          % Function code
Line 1093:    *LDD I (XABLO; STD ABPA2,X          % Disk address
Line 1094:    *LDA I (XABLN; STA ABP31,X          % Byte length
Line 1095:    CALL M5TRANS; GO BUSR

6.2 LALLOPAGE - Page Allocation (Lines 1170-1188)¶

flowchart TD
    A[LALLOPAGE Entry] --> B[Set status PSW1WAIT]
    B --> C[Save swapper message to CPU datafield]
    C --> D[Call ND-500 allocation routine]
    D --> E[Set status 5IALLOPAGE]
    E --> F[Get CPU datafield]
    F --> G{Allocation successful?}
    G -->|Yes| H[Return page address]
    G -->|No| I[Return error]
    H --> J[Call XACT500]
    I --> J
    J --> K[Process next message]

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    style D fill:#9C27B0,stroke:#7B1FA2,stroke-width:2px,color:#fff
    style H fill:#4CAF50,stroke:#388E3C,stroke-width:2px,color:#fff
    style I fill:#F44336,stroke:#D32F2F,stroke-width:2px,color:#fff

7. Communication via 5MPM¶

7.1 Shared Memory Structure¶

flowchart TB
    subgraph "ND-100 Side"
        A[SINTRAN Kernel]
        B[5ACTSWAPPER]
        C[XACTRDY]
    end

    subgraph "5MPM Multiport Memory"
        D[SWMSG - Swapper message buffer]
        E[N500DF - ND-500 datafield]
        F[Swap-wait-FIFO]
        G[Process descriptions]
    end

    subgraph "ND-100 Side (driver level, serving ND-500 process 0)"
        H[5SWAP RT-program / 5SWRT]
        I[LSWPAGE Handler]
        J[LALLOPAGE Handler]
    end

    A --> B
    B --> D
    C --> D
    D --> H
    H --> I
    H --> J
    I --> D
    J --> D
    E --> F

    style D fill:#E91E63,stroke:#C2185B,stroke-width:2px,color:#fff
    style E fill:#E91E63,stroke:#C2185B,stroke-width:2px,color:#fff
    style F fill:#E91E63,stroke:#C2185B,stroke-width:2px,color:#fff

7.2 Key 5MPM Addresses¶

Source: Values verified from SINTRAN L07 symbol files (../NPL-SOURCE/SYMBOLS/L07/SYMBOL-2-LIST.SYMB.TXT)

Symbol	Octal Value	Purpose
SWMSG	110054	Swapper message buffer (request/response)
N500DF.X500DF	-	ND-500 system datafield base
X5SWF	-	Swap-wait-FIFO read pointer
X5SWT	-	Swap-wait-FIFO write pointer
X5MXF	-	FIFO maximum size
X5SWB	-	FIFO base address

8. Complete Swapper Lifecycle¶

sequenceDiagram
    participant P as ND-500 process (page fault)
    participant K as ND-100 driver level
    participant M as Message memory (SWMSG)
    participant S as 5SWAP RT-program (ND-100)
    participant D as Disk

    P->>K: Page fault message (via level-12 driver)
    K->>K: 5ACTSWAPPER
    K->>M: Write request to SWMSG
    K->>M: Check swapper status

    alt Swapper free (PSWWAIT)
        K->>M: Set SWPPING status
        K->>K: XACTRDY (+ MCCO restart of process 0)
        S->>M: Read SWMSG request (waits on PSW1WAIT)
        S->>D: MON 131 ABSLI (disk transfer, ND-100 side)
        D-->>S: Data transfer complete
        S->>M: Write result / MONICO restart
        S->>M: Set PSWWAIT (idle)
        K->>P: ND-500 process reactivated
    else Swapper busy
        K->>M: Insert in Swap-wait-FIFO
        K->>P: Block process (LSWPWAIT)
        Note over K: Later, when current request completes
        K->>M: SWPD4: Check FIFO
        K->>M: Dequeue waiting request
        K->>K: 5ACTSWAPPER for the dequeued request
    end

9. Key Insights for Emulator Developers¶

9.1 The Swapper is NOT Polling¶

The swapper is event-driven:

Process requests service -> 5ACTSWAPPER called (on the ND-100)
XACTRDY evaluates priority -> selects highest-priority work
The ND-500 is (re)activated -> and the 5SWAP RT-program (ND-100) is scheduled to perform the disk work (5SWRT waits on PSW1WAIT, then MON 131)
Completion triggers next -> SWPD4 checks the swap-wait FIFO

9.2 Critical Code Paths to Emulate¶

Path	Source Lines	Purpose
5ACTSWAPPER	2851-2908	Request entry point
XACTRDY	2970-3040	Priority selection
LOWACT500	245, 251, 459	Hardware activation
SWPD4	1031-1066	FIFO processing
LSWPAGE	1070-1114	Disk I/O
LALLOPAGE	1170-1188	Page allocation

9.3 State Transitions to Track¶

stateDiagram-v2
    direction LR

    [*] --> Idle: System start
    Idle --> ProcessingRequest: 5ACTSWAPPER
    ProcessingRequest --> WaitingDisk: LSWPAGE
    WaitingDisk --> ProcessingRequest: Disk complete
    ProcessingRequest --> Idle: SWPD4

    state Idle {
        [*] --> CheckFIFO
        CheckFIFO --> WaitingWork: FIFO empty
        CheckFIFO --> DequeueNext: FIFO has work
    }

ND500-BUS-INTERFACE-REFERENCE.md - authoritative bus-interface spec
ND500-SWAPPER-LOADING-MECHANISM.md - how the swapper is loaded (verified)
ND500-IF-USAGE-DEEP-ANALYSIS.md - IOX commands and 500HIST polling
MP-P2-N500.md - Main driver module analysis
../OS/15-DISK-IO-SUBSYSTEM.md - Disk I/O and queue pools
../OS/17-SCHEDULER-AND-PRIORITIES.md - Task scheduling

11. Verification Checklist¶

[x] Swapper purpose documented (segment loading, page swapping)
[x] State machine documented (LSWPWAIT, LSWPPING, LACTIVE)
[x] 5ACTSWAPPER flow documented with Mermaid diagram
[x] FIFO queue processing (SWPD4) documented
[x] Work triggering mechanisms documented (XACTRDY, LOWACT500)
[x] Disk I/O path (LSWPAGE) documented
[x] Page allocation path (LALLOPAGE) documented
[x] 5MPM communication structure documented
[x] Complete lifecycle sequence diagram included
[x] No speculation presented as fact

Document Version: 2.0 (corrected execution side: 5SWAP runs on the ND-100) Last Updated: 2026-07-08 Source: MP-P2-N500.NPL (lines 1031-1188, 2851-2908, 2970-3040), RP-P2-N500.NPL (lines 16-58)

12. ND-100 -> ND-500 swapper message routing (SWMSG -> 0x240B8)¶

This section carves the ND-100 side of the swapper request message and closes it against the ND-500-side proof in swapper/swapper-k01-deep-analysis.md (sections 3, 4.2, 5) and swapper/swapper-k01.dseg.md (0x240B0-0x240BC message control area).

Provenance rule: the NPL sources (SINTRAN/NPL-SOURCE/NPL/MP-P2-N500.NPL, RP-P2-N500.NPL) are a DIFFERENT REVISION than the L07 bytes the swapper carve is taken from. NPL is treated here as authoritative LOGIC and FIELD-NAMES; the byte-level offsets are the L07 truth taken from SINTRAN/NPL-SOURCE/SYMBOLS/L07/N500-SYMBOLS.SYMB.TXT (assembled symbol table, values octal, names truncated to 5 characters). Labels below: PROVEN (read from carved bytes / a symbol-table value / an NPL statement), INFERRED, OPEN.

12.1 SWMSG field layout (PROVEN offsets, L07 symbol table)¶

All values octal. Offsets are relative to the SWMSG base. SWMSG carries two regions: a low "mic message" region (the words the ND-500 microcode MON mechanism exchanges) and a high swapper-administration region. Symbol names in the L07 table are 5-char truncations of the NPL names.

Field (NPL)	L07 sym	Offset (oct)	Region	Written by / read by	Cite (L07 syms)
MICFU (MICFUNC)	MICFU	000006	mic msg	5ACTSWAPPER writes 3MONCO	line 5266
N500A	N500A	000007	mic msg	disk/param path	line 5745
NUMPA	NUMPA	000012	mic msg	5ACTSWAPPER writes 6	line 5744
FUNCV	FUNCV	000013	mic msg	5ACTSWAPPER writes 0	line 2127
TRAPN	TRAPN	000016	mic msg	trap number (fault path)	line 744
SWPFU (SWAP FUNCTION)	SWPFU	000101	admin	5ACTSWAPPER writes SWACTIVE; SWPDECODER reads	line 3594
RETP2	RETP2	000102	admin	return-value slot	line 925
SWPST (SWAP STATUS/REASON)	SWPST	000103	admin	5ACTSWAPPER writes swap-function/reason	line 3480
HSWPI (-> SWPINFO ptr)	HSWPI	000104	admin	5ACTSWAPPER writes MSGTOSW address	line 6463
SWPIN	SWPIN	000105	admin	cleared on completion	line 4985
SPFLAG	SPFLA	000143	admin	error/flag word	line 4126
XADPR	XADPR	000144	admin	proc-descr address	line 6717

(SWFMAX/SWFMA = 000006, line 4127; SWFUN = 000007, line 4986 - these are the MSGTOSW-relative "swap function" offset and the SWPDECODER upper bound, see 12.3-12.4.)

12.2 What 5ACTSWAPPER packs (PROVEN from NPL logic)¶

SINTRAN/NPL-SOURCE/NPL/MP-P2-N500.NPL, routine 5ACTSWAPPER at NPL line 2857 (octal addr 144762):

line 2866 AD:=CMSGTOSW; *AAX HSWPI; STDTX -> SWMSG.HSWPI(104) := address of MSGTOSW (the SWPINFO pointer)
line 2867 SWACTIVE; *AAX SWPFU-HSWPI; STATX -> SWMSG.SWPFU(101) := SWACTIVE (a state marker, NOT the function code)
lines 2874-2882: X:=MSGTOSW; read MSGTOSW.MICFUNC(6); IF 3SWMESS=D then read MSGTOSW.SWFUN(7), else read MSGTOSW.TRAPN(16) (fault path)
line 2883 X:=SWMSG; *AAX SWPST; STATX -> SWMSG.SWPST(103) := A (comment: "Save reason for activating swapper"); A = MSGTOSW.SWFUN for a message activation, or the trap number for a fault activation
line 2884 A:=6; *AAX NUMPA-SWPST; STATX -> SWMSG.NUMPA(12) := 6
line 2885 A:=0=:D; *AAX FUNCV-NUMPA; STDTX -> SWMSG.FUNCV(13) := 0
line 2887 3MONCO; *MICFU@3 STATX -> SWMSG.MICFU(6) := 3MONCO

So the ND-100 stores the "why the swapper was activated" value in SWPST, not SWPFU.

12.3 SWPFU is the OTHER direction (PROVEN) - the leading candidate is REFUTED¶

SWPDECODER (MP-P2-N500.NPL line 913, octal addr 135443) reads SWMSG.SWPFU as the dispatch index for swapper -> ND-100 paging requests:

line 914 T:=5MBBANK; *AAX SWPFU; LDATX % Swap-function
line 915 IF A >> SWFMAX GO FAR ESWPFATAL (SWFMAX/SWFMA = 6)
lines 917-919 A GOSW into a 7-entry table: ESWPFATAL(0), LNEWSWAP(1), LSWPAGE(2), LPRSUSPEND(3), LALLOPAGE(4), LDATREADY(5), LCLTSB(6)

This is the swapper-issues / ND-100-serves direction and matches the ND-500 side exactly: the swapper's 15 MON 377B (N5SWAP) call sites carry selector VALUES 1,2,4,5,6 plus SWPFA=0o2047 (a code far above SWFMAX -> falls to ESWPFATAL via the bound check) - see swapper/swapper-k01-deep-analysis.md section 3.1. Therefore SWPFU is the swapper->ND-100 request code, and is REFUTED as the source of the swapper's 0x240B8 function code.

12.4 What actually becomes 0x240B8 (PROVEN chain + one INFERRED hop)¶

ND-500 side, PROVEN from the swapper bytes (SINTRAN/ND500/swapper/swapper-k01-pseg.asm):

line 10535 call ...377,$4,$1000225050(=1),$1000440260,$1000440264,b.24 - swapper issues MON 377B sub-function 1 (LNEWSWAP) with 0x240B0 and 0x240B4 as OUT parameters the ND-100 fills
line 10544 w1 := $1000440260 (load [0x240B0])
line 10545 w1 =: $1000440270 (store into [0x240B8]) => [0x240B8] := [0x240B0]
lines 10560-10566 bound check: w test [0x240B8] (>= 0) and w comp2 [0x240B8],$34 ($34 = 0o34 = 28 decimal) => valid range 0..0o34 (0..28)
line 10577 h riom $1000440264,$1000440274,$1000440074+ (DMA the message body from ND-100 addr [0x240B4] into buffer [0x240BC])
lines 10599-10600 w1 := $1000440270; jumpg $1000460630+ (dispatch on [0x240B8] via the 29-entry table at 0x26198)

The bound (0..0o34 = 0..28) and the 29-entry table (array descriptor max_index 0x1C = 28, deep-analysis sec 4.2) are consistent to the byte. The coordinator brief's "0..20" is imprecise; the carved w comp2 ...,$34 gives 0..0o34 = 0..28.

The exact-fit evidence that this code is SWPST (carrying SWFUN): the ND-100 message-to-swapper function codes (the MSW* family, MSGTOSW.SWFUN values) span exactly 0..0o34 in the L07 symbol table - 29 distinct codes matching the 29-entry table:

MSW code (L07 sym)	value (oct)	MSW code (L07 sym)	value (oct)
MSWFI	000000	MSWMC	000014
MSWUF	000001	MSWSP	000015
MSWSO	000002	MSWSG	000016
MSWMI	000003	MSWIS	000017
MSWMD	000004	MSWRS	000020
MSWIN	000005	MSWWB	000023
MSWPO	000006	MSWSW	000024
MSWST (MSWSTART)	000007	MSWPR	000033
MSWFO	000010	MSWDO	000034
MSWIP	000011
MSWPF	000012
MSWME	000013

(L07 symbol lines 5462-5713; names are 5-char truncations, full spellings not recovered except MSWST=MSWSTART and MSWSW=MSWSWAIT which appear spelled out at MP-P2-N500.NPL lines 431 and 464.) The maximum, MSWDO = 0o34 = 28, is exactly the table's max index (0x1C = 28). 5ACTSWAPPER stores MSGTOSW.SWFUN into SWMSG.SWPST (12.2). The ND-100 tests SWFUN against MSWSTART (MP-P2-N500.NPL line 431) and MSWSWAIT (line 464), confirming SWFUN takes MSW* values.

12.5 Verdict¶

SWPFU -> 0x240B8: REFUTED (PROVEN). SWPFU is the swapper->ND-100 request code decoded by SWPDECODER (bound SWFMAX=6, 7-entry table). It is not the ND-100->swapper function code.
SWPST -> 0x240B8: the answer, INFERRED (strong / structurally near-proven). SWMSG.SWPST (offset 0o103) holds the ND-100->swapper "reason/function" = MSGTOSW.SWFUN (an MSW code 0..0o34) for message activations, or a trap number for fault activations. The swapper receives it as the OUT parameter of MON 377B sub-function 1 (LNEWSWAP), stores it at 0x240B0, copies it to 0x240B8 (pseg lines 10544-10545), bound-checks 0..0o34, and jumpg-dispatches. The 29-entry table range 0..0o34 = 0..28 matches the MSW code range 0..MSWDO(0o34) exactly.

OPEN (what would close it to the byte): the single ND-100 instruction that copies SWPST (or the SWFUN it holds) into the MON 377B sub-function-1 OUT parameter that the swapper stores at 0x240B0 is not located in these files, and the NPL revision differs from the L07 bytes. Settling experiments: (a) trace a live 5ACTSWAPPER -> swapper LNEWSWAP round trip and observe which SWMSG word appears at ND-500 [0x240B0]/[0x240B8]; (b) carve the L07 ND-100 LNEWSWAP handler (MP-P2-N500 LNEWSWAP, NPL line 933) and find the OUT-parameter write; (c) run each MSW* activation and record which 0x26198 handler index the swapper reaches.

12.6 Function-code map (0..0o34) - as far as the NPL names them¶

The MSW codes above ARE the swapper's 0..28 dispatch namespace. Full symbolic spellings beyond MSWSTART(0o7) and MSWSWAIT(0o24) are NOT recovered from the available files (the L07 table truncates to 5 chars and no definition block with comments was located). Named/known so far: MSWFI=0, MSWSTART(MSWST)=0o7, MSWPFAULT(MSWPF)=0o12 (used at MP-P2-N500.NPL line 877 as MSWPFAULT SHZ 10), MSWSWAIT(MSWSW)=0o24, MSWDO=0o34 (max). The remaining MSW codes are listed with values above; their full names and per-handler semantics are OPEN.

Section source: SINTRAN/NPL-SOURCE/NPL/MP-P2-N500.NPL (5ACTSWAPPER 2857-2907, SWPDECODER 913-919, lines 431/464/877), SINTRAN/NPL-SOURCE/SYMBOLS/L07/N500-SYMBOLS.SYMB.TXT (offset and MSW* value symbols), SINTRAN/ND500/swapper/swapper-k01-pseg.asm (pseg 10535/10544-10545/ 10560-10566/10577/10599-10600), and the ND-500-side proof in swapper/swapper-k01-deep-analysis.md.