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ND-120 Microcode Version: Identification and the 013/K Question

Scope: How to identify the ND-120 CPU microcode ("microprogram") version, what version the carved SINTRAN L-VSX-500 (L07) system actually carries, and how to obtain the older 013/K microcode.

Status: Investigation complete. VERIFIED / UNCERTAIN tags used throughout.

1. The version byte (VERIFIED)

The ND-120 microword is 64 bits wide. The microcode version is stored in the low 8 bits of the 64-bit microword at microword address octal 020 (decimal 16, the 17th microword, zero-based).

Calibrated against the known-good ND-120 EPROM dump (version L) in the ND-120 FPGA recreation repo (Code/Microcode/ -> wcs_image.hex, line number = CSA/WCS word address):

microword o020 = 7b80 0080 8006 800c   (64-bit)
low 8 bits     = 0x0c = octal 014 = decimal 12

The low-8 value is the alphabet position of the version letter:

low-8 (hex) octal decimal letter "revision/letter"
0x0b 013 11 K 013/K
0x0c 014 12 L 014/L

So "013/K" literally means microword-020 low-8 = octal 013 = K, and the L EPROM reads octal 014 = L. Mapping VERIFIED against the L EPROM.

Recipe to read the version from a raw ND-120 microword array

For a raw microword image stored as big-endian 16-bit ND-100 words (the on-disk ND word order), where a 64-bit microword = 4 consecutive 16-bit words:

  1. Word packing (per the EPROM->WCS mapping word = {P(RF=3),P(RF=2),P(RF=1),P(RF=0)}, RF=0 -> bits[15:0]): the first 16-bit word of the four is the low group (bits 15:0), the fourth is the high group (bits 63:48).
  2. Microword o020 starts at word offset 16 * 4 = 64 (byte offset 128) from the start of the array.
  3. Version = low byte of the first of those four 16-bit words (bits 7:0 of the RF=0 group). In a big-endian .bin that is the second physical byte of that 16-bit word (e.g. word 0x800c is stored 80 0c; the version is 0c).
  4. Decode: octal 013 = K, octal 014 = L (low-8 = alphabet position).

2. What the carved L07 system actually carries (VERIFIED)

The carved segments (see ../../tools/sintran-segment-carver/versions/L-VSX-500/segments/):

Segment File Description Contents
0113 113-S3IU120.bin "Image of ND-120 Microprogram" ND-100 loader program code
0112 112-S3SU120.bin "Save of ND-120 Microprogram" loader data / save area

IMPORTANT (VERIFIED): these segments are NOT a raw 64-bit microword array. The premise that microword o020 can be indexed directly out of segment 112/113 does not hold for this system:

  • Segment 113-S3IU120.bin (32768 bytes) is ND-100 instruction code throughout. All four 16-bit stride-4 phases have identical entropy (~9.8 bits) and share the same top values (0xa803, 0xcc1d, 0x0902 = ND-100 opcodes). There is no low-entropy "tag column" anywhere, i.e. no periodic 64-bit microword structure.
  • It contains the ASCII reference (SYSTEM)MACM-AREA:DATA -- the loader's runtime microcode area.
  • On the running L07 system disk (SMD0.IMG), (SYSTEM)MACM-AREA:DATA is 0 bytes (a 64-page scratch area, empty on disk -- populated only at load time).
  • Neither carve matches the L EPROM in any byte arrangement (LE/BE, hi-first/lo-first, byte-plane), so the microcode is embedded in the loader in a serialized/packed form, not a plain array.

Conclusion (VERIFIED by distribution manifest): segment 113 (S3IU120) is the loaded image of the ND-120 microprogram loader MACM-1718L. The L07 distribution floppy 250305L07-XX-01D ships (SYSTEM)MACM-1718L:BPUN -- so this system's ND-120 microcode is version L (014/L), the same version as the ND-120 EPROM dump. It is NOT 013/K.

UNCERTAIN: reading the exact microword-020 byte out of the carved image would require reversing MACM's embedded/serialized microcode payload (or running the loader and dumping the WCS). The version is established here from the distribution file name (MACM-1718L) rather than from a raw microword read, because no raw microword array is present in the carve.

3. Where 013/K lives, and how to get it (VERIFIED locations)

The ND-120 microprogram ships as (SYSTEM)MACM-1718<letter>:BPUN (a ~24-page ND-100 BPUN loadable -- the loader with the microcode payload). Indexed from the ND floppy archive (~/repos/ndfloppy, floppies.json / floppifiles.json):

Microcode File Floppy image label(s)
013/K (SYSTEM)MACM-1718K:BPUN N-10-102-I (only), paired with SINTRAN-I:DATA
014/L (SYSTEM)MACM-1718L:BPUN 250305L07-XX-01D (our L07), 250306M06-XX-01D (M06), N-250306K05--01D (K05), N-220046K03--01D (K03), ND-BFLY-SIN-J01 (J01), N-100-1001-I, N-100-1002-I, N-102-2921-I

Key insight (VERIFIED): the microcode letter is independent of the SINTRAN release letter. SINTRAN J01, K03, K05, L07 and M06 distribution floppies all ship MACM-1718L. So "go to an older SINTRAN version" (K03/K05) does not yield the K microcode -- those already carry L. The 013/K microprogram is found on exactly one archived floppy: N-10-102-I (an early SINTRAN-I release).

Plan to obtain 013/K

  1. Get the floppy image N-10-102-I. The ndfloppy repo holds only JSON listings, not the images; the images are hosted at the storage backend referenced by its deploy script (ndlib / https://ndlib.hackercorp.no). Fetch the N-10-102-I image from there (or any physical/archived copy of that floppy).
  2. Extract the file: ndtool -x "(SYSTEM)MACM-1718K:BPUN" N-10-102-I.<img>
  3. MACM-1718K:BPUN is the loader-with-payload (same shape as segment 113), not a raw microword array. To recover raw microwords for a direct o020 read, either:
    • (a) diff MACM-1718K:BPUN against MACM-1718L:BPUN (extractable from the L07 floppy 250305L07-XX-01D); the differing region is the microcode payload, and the version byte sits where microword o020 maps; or
    • (b) load/interpret the MACM loader to populate the WCS, then dump the WCS and index microword o020 with the recipe in section 1; or
    • (c) if a K-version EPROM dump (AM27256 pair) surfaces, apply the section-1 recipe directly (fastest, most reliable).
  4. Confirm success: microword o020 low-8 = 0x0b (octal 013) = K.

3B. MACM-1718K (013/K) — verified

A copy of MACM-1718K.BPUN (31916 bytes) was analysed directly. Findings below use VERIFIED / UNCERTAIN tags.

BPUN container (VERIFIED)

The file is a standard ND BPUN (bootable-punch loader). Layout:

Region File offset (bytes) Contents
Null leader 0x000..0x07e (127 bytes) zero fill
Preamble / bootstrap 0x07f..0x1ad octal loader words as 7-bit-ASCII-with-parity (mask 0x7F), one per CR/LF group
! start-of-data marker 0x1ae 0xA1 ('!' | parity)
Load block header + data 0x1af.. address, count, data, checksum, action (see below)
Trailer 0x7c2f..0x7cab leftover leader/message bytes

Preamble decode (mask 0x7F) is a sequence of octal bootstrap words (160616 146101 134021 146157 134017 ...) — the toggle-in loader, not a version string. Parsed per the BPUN rules: Start (exec) = octal 137777, Boot = octal 160616. There is no literal "K"/"013"/date banner; the file's version identity is its name MACM-1718K (see section 3) plus the driver text below.

Load block map (VERIFIED)

Exactly one load block:

Field Value
Block header file offset 0x1af
Load address octal 101304 (decimal 33476)
Word count 15676 words
Data file offset 0x1b3..0x7c2e (31352 bytes, big-endian 16-bit ND words)
Checksum (file) octal 143623
Checksum (recomputed) octal 143623 — valid
Action 0 (execute at Start)
Loaded span octal 101304 .. 137777 (decimal 33476..49151)

The reconstructed loaded image is extracted to ../../tools/sintran-segment-carver/versions/L-VSX-500/re/MACM-1718K-loaded-image.bin (31352 bytes, big-endian 16-bit ND words, load address octal 101304, sha256 8f0406969b6d3188b8b781713f00d8070bb6e82cae92a321321adaf95f79ad95).

What the block actually contains (VERIFIED)

The block is the MACM WCS-loader program, not a flat microword array. Masked-ASCII strings in the data are an ND-100 disk driver and its error handler: DEVNO, 0 % DEVICE NUMBER (01540 OR 01550), CY, 0 % CYLINDER, SRFSC, BANKN, ADRES, WORDC, RSCON, 0 % SEEK CONDITION, REGI, 0 % BITS 017-011 ARE ERROR INDICATORS, and the message BELOW FOLLOW 11 WORDS THAT CONTAIN ERROR INFORMATION ABOUT THE LAST ERROR. So MACM reads/loads the microcode into the WCS at runtime.

Microword o020 could NOT be read directly (UNCERTAIN)

The premise that microword octal 020 can be indexed out of the BPUN payload does not hold here — same structural result as the L carve in section 2:

  • The data payload is 31352 bytes, far smaller than a full 8192-microword × 8-byte array (64 KB), so the microwords are not stored as an uncompressed 64-bit array.
  • A byte-signature search for microword o020 — both the K pattern (...800b) and the L pattern (7b8000808006800c) — finds nothing in ND-word big-endian, ND-word little-endian, or reversed group order.
  • A longest-common-substring correlation of the known-good L microcode against this payload (P-stream hi<<8|lo BE and LE, lo-plane, hi-plane, plane concatenations) yields no significant common run (best 23 bytes, coincidental). The microcode is therefore embedded in the loader in a serialized/shuffled (or compressed) form, not the EPROM/WCS byte layout.
  • The carved L loaded image 113-S3IU120.bin shares zero common run with this K payload and lacks these driver strings, so it is not a usable byte-level L reference for a diff either.

Conclusion: the BPUN container, single load block, checksum, and loader identity are VERIFIED; the file is the 013/K microprogram by name/provenance (section 3). Directly reading microword o020 low-8 = 0x0b to confirm K from this file is not possible by inspection — it requires reversing MACM's embedded/serialized microcode payload, running the loader to populate and dump the WCS, or obtaining a K-version EPROM dump (then apply the section-1 recipe). A byte-level K vs L microword delta likewise awaits a comparable L artifact (a MACM-1718L:BPUN or a K/L EPROM pair); the carved 113-S3IU120.bin is not byte-compatible with this loader and cannot serve as the L side.

4. Not the microcode (disambiguation)

These similarly named SYSTEM files are development tools, not ND-120 CPU microcode:

  • MAC-1628C, FMAC-1408D, F32-MAC-1628C, F32-FMAC-1920C -- the MAC macro/micro assembler toolchain (there is a whole (BPUN-FILES) directory of these).
  • DMAC-1915G:BPUN -- a segment debugger/dump tool (strings: "PREVIOUS B", "RETURN ADDRESS", "segment is not modifyable").
  • MICRO-5x00-*, MIC-5x00-90-500, MIC-REGISTER, MIC-SEQUENCE -- ND-500 microcode/microtest, not ND-120.

Only MACM-1718<letter> is the ND-120 CPU microprogram.

References

  • ND-120 EPROM / WCS calibration source: ND-120 FPGA recreation repo, Code/Microcode/wcs_image.hex (version L), microword field layout in Verilog/CPU-BOARD-3202/circuit/CPU_PROC_CGA_33.v.
  • ND-06.031.1 ND-110 and ND-120 Microprogrammer's Guide (microword field semantics).
  • Carved segments: ../../tools/sintran-segment-carver/versions/L-VSX-500/segments/ (113-S3IU120.bin, 112-S3SU120.bin) and versions/L-VSX-500/segment-facts.json.
  • ND floppy archive index (floppies.json / floppifiles.json) for MACM-1718K/L floppy locations.