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DOM / SEG File Format (New ND-500(0) Domain Format)

:DOM (domain) and :SEG (free segment) are the file types produced by the newer ND Linker (ND-211224) and consumed directly by the ND-500(0) Monitor to run a program. They replace the old :PSEG/:DSEG/:LINK + DESCRIPTION-FILE:DESC scheme - see DESCRIPTION-FILE-FORMAT.md for that older format and why it needed a separate index file. CONVERT-DOMAIN (ND-500 vendor program, CONVERT-DOM-A03.DOM) migrates old-format domains into :DOM/:SEG.

Primary source - VERIFIED, code-level ground truth, stronger than the manual alone:

src/include/nd500/dom.h in the pcc-nd500 repository - the exact #pragma pack(1) struct layout used by dom_utils.c (libdom.a), consumed by both nd500-dis and nd500-dump in the pcc-nd500 toolchain to load and run real .DOM files (this is the code path behind the working HELLO.DOM compile/link/run chain documented in the nd500-apps skill) - not just a transcription of the manual's prose.

Secondary source: ND-860289-2-EN ND Linker User Guide and Reference Manual.md (NDInsight Reference-Manuals/), Appendix E "The New Domain Format" - the narrative description; the header field list there is qualitative only (no byte offsets), which is why dom.h's concrete offsets are the primary source here.

All multi-byte fields are big-endian (ND-500 native byte order).

1. Overall file layout

0x0000  Domain/Segment Header (4096 bytes = 2 pages of 2048; page 2 is reserved)
0x1000  Debug info
        Link info
        Program/Data segments (slave segments, DOM only)

Only pages actually used are allocated on disk. A :DOM file with no external links can be copied with a plain @COPY-FILE (everything needed is inside it); a :SEG file holds exactly one program+data segment pair, referenced by one or more :DOM files via a link key match (see section 5).

2. File Header (16 bytes, offset 0x00 - shared by DOM and SEG)

Offset Field Size Meaning
0x00 LINKLOCK 4 Random lock value. A domain linked to a :SEG file records this value as its LINKKEY; they must match at load time or the segment is considered a different version.
0x04 VERSION 1 ND Linker version that produced this file.
0x05 REVISION 1 ND Linker revision.
0x06 FLAGS 1 Bit 3: trap block valid. Bit 4: is a :DOM file (vs :SEG). Bit 5: root/multidomain. Bit 6: SINTRAN-III domain. Bit 7: is ND-500/5000.
0x07 MACHINE 1 Target machine type.
0x08 OS_ID 1 Operating system ID.
0x09 reserved 1
0x0A SUBSYSTEM_KEY 6

dom_is_dom_file()/dom_is_nd500_file()/dom_is_sintran_iii() test bits 4/7/6 of the FLAGS byte directly.

3. DOM-specific part (offset 0x10 - 0xC6)

Offset Field Size Meaning
0x10 PRIVILEGES 8 (4x16-bit) Domain privileges.
0x18-0x25 (padding) 14
0x26 MOTHER 8 Domain Reference (below) to the mother domain.
0x2E CHILDREN[16] 128 (16x8) Domain References to up to 16 child domains.
0x2E+128=0xAE .. 0xC5 (padding) to 0xC6

Domain Reference (8 bytes): MIN_INDEX(u16) + MAX_INDEX(u16) = byte range into the name pool for this domain's name, + LINK_KEY(u32) which should match the referenced domain's LINKLOCK.

4. Common part (offset 0xC6 - 0x108, both DOM and SEG)

Offset Field Size Meaning
0xC6 FREIND 2 Free byte pointer into the name pool.
0xC8 DEB_LB 4 Debug info lower bound (file offset).
0xCC DEB_SZ 4 Debug info size.
0xD0 LINK_LB 4 Link info lower bound.
0xD4 LINK_SZ 4 Link info size.
0xD8 STADDR 4 Start address.
0xDC RESTADDR 4 Restart address.
0xE0 THA 4 Trap Handler Address.
0xE4 MTE2 / 0xE8 MTE1 4+4 Memory Trap Enable (64-bit mask, high then low word).
0xEC OTE2 / 0xF0 OTE1 4+4 Own Trap Enable (64-bit mask).
0xF4 CTE2 / 0xF8 CTE1 4+4 Child Trap Enable (64-bit mask).
0xFC TEMM2 / 0x100 TEMM1 4+4 Trap Enable Mod Mask (64-bit mask).
0x104 PRIORITY 4 Process priority.

(Common part ends at 0x108.)

5. Segment part (28 bytes) - the building block for one program OR one data segment

Field Size Meaning when NOT linked Meaning when ATT.LINKED_SEGMENT bit set
LB 4 Lower bound = file offset of segment content Name-pool index of the linked-to segment's name
SZ 4 Size in bytes LINKKEY to match against the target :SEG file's LINKLOCK
ATT 4 Attribute bitmask (section 6) (same)
FLA 4 Fixed Lower Address = virtual load address
FUA 4 Fixed Upper Address
AFA 4 Absolute Fix Address
MINP 2 Min pages MIN name-pool index (if linked)
MAXP 2 Max pages MAX name-pool index (if linked)

A Segment Descriptor (56 bytes) = one Program Segment Part + one Data Segment Part, back to back.

6. Segment ATT (attribute) bits

Bit Name Meaning
10 FIXED_ABSOLUTE
11 FIXED_CONTIGUOUS
12 FIXED_SCATTERED
13 SEGMENT_USED Slot contains valid data - test this before reading a slot.
14 LINKED_SEGMENT LB/SZ (and MINP/MAXP) hold name-pool index / link key, not offset/size - see section 5.
15 ROUTINE_VECTOR
16 INSUFF_LOADED
17 FORTRAN_COMMON
18 OTHER_MACHINE
19 START_VECTOR Start vector on this segment.
20 INDIRECT
21 SHARED_ND100
22 COPY_CAPABILITY
23 CLEAR_CAPABILITY
24 CACHE
25 FILE_AS_SEGMENT
26 EMPTY_DATA
27 SHARED_DATA
28 PROGRAM_SEGMENT
29 SWAP_ON_SWAPFILE
30 PARAMETER_ACCESS
31 WRITE_PERMIT

7. DOM header - full layout (4096 bytes)

Offset Field Size
0x000 File Header 16
0x010 DOM-specific part to 0xC6
0x0C6 Common part to 0x108
0x108 Indirect segments[32] 32 x 10 = 320, to 0x248
0x248 LANGUAGE_MSAL 4
0x24C IDX_FREE_MIN/MAX 2+2
0x250-0x253 (padding) 4
0x254 Segment table: 32 x Segment Descriptor (56 bytes each) 1792, to 0x954
0x954 Name pool to 0x1000

Indirect Segment (10 bytes): MIN_INDEX(u16) + MAX_INDEX(u16) + LINK_KEY(u32) + SLOG(u8, logical segment number) + reserved(u8).

To read segment N's descriptor: header + 0x254 + N*56 (N = 0..31). Program part first (28 bytes), then data part (28 bytes). Check ATT.SEGMENT_USED before trusting the slot.

8. SEG header - full layout (4096 bytes)

A :SEG file holds exactly one segment pair (no domain-level bookkeeping - mother/child, segment table, language mask):

Offset Field Size
0x000 File Header 16
0x010-0x013 (padding) 4
0x014 Program Segment Part 28, to 0x030
0x030 Data Segment Part 28, to 0x04C
0x04C-0x06F (padding) to 0x070
0x070 PROG_LOGSEG 1
0x071 DATA_LOGSEG 1
0x072 N100_COUNT 2
0x074 N100 RT segments[10] 10 x 12 = 120, to 0xEC
0xEC-0xC5 (pad to Common part)
0x0C6 Common part to 0x108
0x108 Indirect segments[32] 320, to 0x1C8
0x1C8 LANGUAGE_MSAL 4
0x1CC IDX_MIN/MAX (ID message) 2+2
0x1D0-0x1D3 reserved 4
0x1D4 Linked segments[32] 32 x 16 = 512, to 0x3D4
... Name pool to 0x1000

ND-100 RT Segment (12 bytes): N100SW[6] (name) + N100SNO(u16) + N500LOGPA(u16, map address in ND-500 logical memory, pages) + N100SIZE(u16, pages).

Linked Segment (16 bytes, SEG files only): PROG_MIN/MAX(u16 each) + PROG_KEY(u32) + DATA_MIN/MAX(u16 each) + DATA_KEY(u32).

9. Name pool

A byte pool at the end of the header (0x954..0x1000 for DOM, 0x454..0x1000 for SEG). A name is pool[min_index .. max_index). min_index==0 || max_index==0 || min_index>=max_index means "no name."

10. Open items

  • FLAGS byte (offset 0x06) is now confirmed against a real, freshly-produced .DOM: CONVERT-DOM-A03 converting LINKAGE-LOAD-H02 (2026-08-10, see ../ND500-APPS/CONVERT-DOM-A03/userguide.md) wrote 0xF8 = bits 3/4/5/6/7 set = TRAPBLOCK_VALID + IS_DOMAIN_FILE + IS_ROOT_DOMAIN + IS_SINTRAN_III + IS_ND500, exactly matching this doc's bit table.
  • The rest of the segment table, name pool, and common part have no field-by-field validation report against a real .DOM beyond what the working nd500-dis/ nd500-dump/nd500x runtime already exercises implicitly (they run real DOMs successfully, which is strong indirect validation, but no dedicated byte-level walkthrough doc exists yet).
  • DOM_COMMON_OFFSET/DOM_STADDR_OFFSET macro names in dom.h (0xC6, 0xD8) match this doc's Common Part table exactly - kept in sync intentionally; if dom.h changes, update this doc too.