*** CVT (ConVerT containers)
*** Document revision: 1.2
*** Last updated: March 11, 2004
*** Contributors/sources: Joe Forster/STA
These are sequential representations of GEOS files, both sequential and
VLIR. In order to be transmitted and up/downloaded, they must be converted
to this intermediate format because the file's INFO block must be included.
Note that the track/sector references at the beginning of each sector are
not included here, making the block size 254 bytes. Also, any values in
track/sector references are invalid, since the value is sure to change once
the file is converted back from CVT to a GEOS format.
I will not include much of the GEOS file layout details here, as you can
read the GEOS.TXT document to get the information.
With CVT's that contain VLIR files, there are four distinct sections:
signature, info, record and data. CVT's that contain non-VLIR files (i.e.
standard GEOS sequential) do not include the record block.
The first part, which exists in both CVT types, is the signature block.
It contains the complete directory entry and CVT file signature.
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F ASCII
----------------------------------------------- ----------------
0000: 83 00 00 44 45 53 4B 20 54 4F 50 A0 A0 A0 A0 A0 ???DESK?TOP?????
0010: A0 A0 A0 00 00 01 04 58 08 13 0D 23 78 00 50 52 ?????..X...#x?PR
0020: 47 20 66 6F 72 6D 61 74 74 65 64 20 47 45 4F 53 G?formatted?GEOS
0030: 20 66 69 6C 65 20 56 31 2E 30 00 00 00 00 00 00 ?file?V1.0??????
0040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
00A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
00B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
00C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
00D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
00E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
00F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 .. .. ??????????????..
Byte:$00-1D: Complete directory entry. Note that the first two bytes of
*any* directory entry are never used, and thus are not
incuded here either.
1E-39: File signature. It can contain "PRG formatted..." or "SEQ
formatted...". Here we can check that the CVT is really
what it claims.
3A-FF: Usually $00
What follows the signature block is the complete GEOS file INFO block.
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F ASCII
----------------------------------------------- ----------------
00F0: .. .. .. .. .. .. .. .. .. .. .. .. .. .. 03 15 ................
0100: BF FF FF FF 92 49 01 FF FF 01 80 00 1D BF FF DD +????I.??.??.+??
0110: A0 00 5D BF FF C1 A0 00 5D A1 C6 55 A0 29 5D A0 ??]+?+??]?+U?)]?
0120: C9 41 A1 09 41 B9 D6 41 A8 00 41 BF FF C1 80 00 ?A?.A??A??A+?+??
0130: 1D 9C 00 15 9C 00 15 80 00 1D 80 00 01 FF FF FF .£?.£?.??.??.???
0140: 83 04 01 56 19 55 19 75 51 64 65 73 6B 54 6F 70 ?..V.U.uQdeskTop
0150: 20 41 4D 20 20 56 32 2E 30 00 00 00 00 42 72 69 ?AM??V2.0????Bri
0160: 61 6E 20 44 6F 75 67 68 65 72 74 79 00 00 00 00 an?Dougherty????
0170: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0180: 00 00 00 00 00 4C 2A 5B 4C 59 5D 4C A7 61 4C 3A ?????L*[LY]L?aL:
0190: 62 AD 8A 84 D0 01 60 20 7E 23 20 9C 55 73 65 20 b????.`?~#?£Use?
01A0: 74 68 65 20 64 65 73 6B 54 6F 70 20 74 6F 20 6D the?deskTop?to?m
01B0: 61 6E 61 67 65 20 61 6E 64 20 6D 61 6E 69 70 75 anage?and?manipu
01C0: 6C 61 74 65 20 79 6F 75 72 20 66 69 6C 65 73 2E late?your?files.
01D0: 00 03 20 E3 5C 68 85 FB 20 4F 61 20 13 61 20 32 ?.??\h???Oa?.a?2
01E0: 61 20 F2 5C A9 0C 20 CC 49 A9 2E 85 13 A9 F9 85 a??\?.??I?.?.???
01F0: 12 A9 2F 85 15 A9 01 85 14 A9 84 85 .. .. .. .. .?/?.?.?.???....
The third block is the RECORD block. In the sequential version of the
CVT, this block won't exist. The way to well if the file is VLIR or
sequential is to look at byte position 23 of the directory entry (from
above, it's value is $01). If it's a $00, the file is sequential, if it's
$01 it's VLIR.
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F ASCII
----------------------------------------------- ----------------
01F0: .. .. .. .. .. .. .. .. .. .. .. .. 43 41 0A 0B ............CA..
0200: 0B F4 0A 8C 0B A1 09 70 00 00 00 00 00 00 00 00 .???.??p????????
0210: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0220: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0230: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0240: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0250: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0260: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0270: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0280: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
0290: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
02A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
02B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
02C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
02D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
02E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ????????????????
02F0: 00 00 00 00 00 00 00 00 00 00 .. .. .. .. .. .. ??????????......
Note that the RECORD block is modified from the original GEOS entry.
Instead of containing the track and sector references, we now have the
sector count and the size of the last sector in the chain. Looking over the
block above, we get the following usage chart:
Count Size Comment
----- ---- --------------------------------------
43 41 Sector count=67, last sector index=$41
0A 0B Sector count=10, last sector index=$0B
0B F4 Sector count=11, last sector index=$F4
0A 8C Sector count=10, last sector index=$8C
0B A1 Sector count=11, last sector index=$A1
09 70 Sector count=9, last sector index=$70
00 00 No more records.
Two things of interest can be noted from the record block...
1. When a 00/00 is encountered, the record block is done.
2. When a 00/FF is encountered, the record does not exist (see the
GEOS.TXT format for more info on invalid records), but the entry must
still be made in the re-created RECORD block.
From here on we have the actual data, all of the record chains strung
together to form one long file. All of this data must be broken apart to
form the original records that GEOS expects.
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F ASCII
----------------------------------------------- ----------------
02F0: .. .. .. .. .. .. .. .. .. .. A9 00 8D EE 04 A4 ..........????.?
0300: FE B9 86 84 30 06 29 0F C9 02 D0 12 A4 70 B9 86 ????0.).?.?.?p??
0310: 84 30 06 29 0F C9 02 D0 05 A9 07 8D A0 1D 20 1E ?0.).?.?.?.??.?.
0320: 23 20 04 1A 8A D0 20 20 12 1A 18 A9 00 6D F4 03 #?..????...??m?.
0330: 8D F4 03 A9 03 6D F5 03 8D F5 03 20 C5 22 20 7C ??.?.m?.??.?+"?|
0340: 1B 20 04 1A 20 6B 1A A9 08 8D A0 1D B8 50 53 8D .?..?k.?.??.?PS?
0350: EE 04 20 12 1A A2 00 A4 70 20 3F 24 C9 04 B0 3F ?.?..???p??$?.??
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