VECTOR 4/8086 - Type 21h Full SYSTEM FILE Load (10B8 → FF4C)From Inside a Vector Graphic SX/5000 (Vector 4/8086 variant)

Listings: 02-floppy-load.asm (10B8–11BD) · 03-type21-helpers.asm · type21-outline.asm
Related: Floppy load path · Handoff 13A9 → FF4C · Error codes

Entered when after floppy header validate:

(2442) & C0h == 80h
(2442) & 3Fh == 21h

Sector 0 already at 2400h.

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Pipeline

10B8  Setup dir LBA / entry count
  │
  ├─ loop CALL 11EE          ; next 32-byte dirent @2200
  │     skip E5; match 11-char name @241E
  │     on match: (201D) = alloc index from dirent+1A
  │
  ├─ 14A8 → 2600h            ; allocation map
  │
  ├─ 1231 → 2200h            ; file phase 1 (header block)
  ├─ 1231 → 2200h            ; phase 2 (version/'C'/config)
  ├─ bulk: 0420 + 1231       ; body into mapped pages
  │
  ├─ 12B1 / 12FB             ; runtime tables 6600/6660
  └─ JP 13A9 → mapper walk → JP FF4C

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1. Directory setup (10B8–10DA)

normalize (2411) entry count (shift with B=08)
dir_start LBA = 2*(2416)+1 → (200C)
(200A) = count + dir_start     ; data base related
(201C)=(2015)=0

Var	Role
(2411)	Remaining dir entries (decremented in 11EE)
(2416)	Factor for dir LBA and map read count
(200C)	Next directory sector LBA
(200A)	Base LBA for data blocks
(201C)	Entry index 0…15 in current sector
(201A)	Pointer to current dirent in 2200

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2. Directory search — 11EE + name match

Loop (10DD)

CALL 11EE
CF → 11C0 A=7
NZ → 155D
(HL)==E5 → next
compare 11 bytes vs (241E), RES 7,(HL)
match: HL+=000Fh; (201D)=word at +1Ah

Dirent (32 bytes)

Off	Field
+00	E5=free; else name
+00…+0A	11-char name vs 241E
+1A…+1B	Initial allocation-map index

11EE

if (2411)==0 after dec: SCF RET
if (201C)==0: read (200C)++ → 2200, (201A)=2200
inc (201C) mod 16
return HL=current dirent; (201A)+=20h

16 entries × 32 bytes = one 512-byte sector.

Name is not in ROM — only on disk at header offset +1Eh.

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3. Allocation map @ 2600h

A=(2416), DE=0001, BC=0, HL=2600
CALL 14A8

1272 — next block (12-bit packed, 2 per 3 bytes)

index = (201D)
byte_off = (index*3)/2 ; CF = odd half
w = word at 2600+byte_off
if odd: w >>= 4
w &= 0FFFh
(201D) = w                 ; chain next index
if old_index==0 or ==0FF0h: SCF RET   ; EOF
DE = old_index - 2         ; disk block number
NC RET

Model: linked chain of 12-bit indices; physical LBA = block*(240D)+(200A).

1231 — next file sector → HL

if (2015)==0:
  CALL 1272 → DE block
  (200F) = DE*(240D)+(200A)
inc (2015); if ==(240D): (2015)=0
read 1 sector at (200F)++ into HL via 14A8

Var	Role
(240D)	Sectors per allocation block
(2015)	Sector within block
(200F)	Next absolute sector LBA
(201D)	Map chain cursor

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4. File body phases (1119–11B5)

Phase 1 @ 2200

CALL 1231
(2200)==(2442) else #4
(2227)→67F1; (2229)→67F3; (2223)→2018
if (5FDD)==0: require (2223)<00D8h else #7
LDIR 2300→6500, BC=80h

Phase 2 @ 2200

CALL 1231
(2246) ≤ "01" (word); (2248)=='C' else #4
LDIR 224C→244C, BC=B4h

Phase 3 bulk

(2016)=0004
loop:
  DE=(2016); CALL 0420      ; map bank
  CALL 1231
  (2016)+=2; (2018)--
until (2018)==0
CALL 12B1 / CALL 12FB
JP 13A9

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5. Config builders

12B1: zero 6600…; for 8 ROM ids @09AA, match 12-byte records in @244C, copy to table.

12FB: zero 6660…; media templates @09B9/@09C6 from (2442)&30h; optional Winchester probe if (09AA)≠0.

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6. Handoff 13A9 → JP FF4C

Full write-up: Handoff 13A9 → FF4C · 08-handoff-13A9.asm

1. Build param block @67E0 (FE00/FE60, bases from 5FDD, EA+file words as 8086 far-jump image at 67F0).
2. Copy stub 0573→674C (not executed here).
3. Optional swap 67F0↔︎77F0 if large RAM.
4. Reprogram mapper port 16h (banks + CE, final 3F/7F).
5. JP FF4C — entry outside boot ROM under new map; never returns to menu.

Simple (non-21h) boot uses JP 2400 instead.

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7. Errors (type 21h)

Code	Path	Cause
HW 1–8	155D	Controller / read
Sys 3	11C0	Unexpected EOF from 1231
Sys 4	11C0	Incompatible header/version/'C'
Sys 7	11C0	Dir exhaust or size limit

See Error codes.

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8. Memory during load

2400   SYSTEM header (sector 0)
2200   dir / file structure scratch
2600   allocation map
6500   80h copy from first file block
6600   drive config table
6660   media config
67E0   handoff block
…      bulk via 0420-mapped windows
FF4C   transfer address

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9. Open questions

1. Exact 11-byte name on real media (241E)
   
2. Confirm alloc chain semantics with a disk image
   
3. Code at FF4C after remap (Z80 vs 8086)
   
4. Meaning of EA/E40C fields at 67EE–67F0