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docs/Commodore/CVT.TXT

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*** CVT (ConVerT containers)
*** Document revision: 1.3
*** Last updated: Oct 1, 2007
*** Compiler/Editor: Peter Schepers
*** 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 (and record block
for a VLIR) 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 ƒúúDESKúTOP     
0010: A0 A0 A0 00 00 01 04 58 08 13 0D 23 78 00 50 52    úú..X...#xúPR
0020: 47 20 66 6F 72 6D 61 74 74 65 64 20 47 45 4F 53 GúformattedúGEOS
0030: 20 66 69 6C 65 20 56 31 2E 30 00 00 00 00 00 00 úfileúV1.0úúúúúú
0040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
00A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
00B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
00C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
00D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
00E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
00F0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 .. .. úúúúúúúúúúúúúú..
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-FD: 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 ¿úúú’I.úú.€ú.¿úÝ
0110: A0 00 5D BF FF C1 A0 00 5D A1 C6 55 A0 29 5D A0  ú]¿úÁ ú]¡ÆU )] 
0120: C9 41 A1 09 41 B9 D6 41 A8 00 41 BF FF C1 80 00 ÉA¡.A¹ÖA¨úA¿úÁ€ú
0130: 1D 9C 00 15 9C 00 15 80 00 1D 80 00 01 FF FF FF .œú.œú.€ú.€ú.úúú
0140: 83 04 01 56 19 55 19 75 51 64 65 73 6B 54 6F 70 ƒ..V.U.uQdeskTop
0150: 20 41 4D 20 20 56 32 2E 30 00 00 00 00 42 72 69 úAMúúV2.0úúúúBri
0160: 61 6E 20 44 6F 75 67 68 65 72 74 79 00 00 00 00 anúDoughertyúúúú
0170: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0180: 00 00 00 00 00 4C 2A 5B 4C 59 5D 4C A7 61 4C 3A úúúúúL*[LY]L§aL:
0190: 62 AD 8A 84 D0 01 60 20 7E 23 20 9C 55 73 65 20 b­Š„Ð.`ú~#úœUseú
01A0: 74 68 65 20 64 65 73 6B 54 6F 70 20 74 6F 20 6D theúdeskTopútoúm
01B0: 61 6E 61 67 65 20 61 6E 64 20 6D 61 6E 69 70 75 anageúandúmanipu
01C0: 6C 61 74 65 20 79 6F 75 72 20 66 69 6C 65 73 2E lateúyourúfiles.
01D0: 00 03 20 E3 5C 68 85 FB 20 4F 61 20 13 61 20 32 ú.úã\h…ûúOaú.aú2
01E0: 61 20 F2 5C A9 0C 20 CC 49 A9 2E 85 13 A9 F9 85 aúò\©.úÌI©.….©ù…
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 tell 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 .ôúŒ.¡úpúúúúúúúú
0210: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0220: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0230: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0240: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0250: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0260: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0270: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0280: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
0290: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
02A0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
02B0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
02C0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
02D0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
02E0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 úúúúúúúúúúúúúúúú
02F0: 00 00 00 00 00 00 00 00 00 00 .. .. .. .. .. .. úúúúúúúúúú......
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=$70
00 00 No more records.
Two things of interest can be noted from the record block...
1. When a 00/00 is encountered, the record block is done.
2. When a 00/FF is encountered, the record does not exist (see the
GEOS.TXT format for more info on invalid records), but the entry must
still be made in the re-created RECORD block.
From here on we have the actual data, all of the record chains strung
together to form one long file. All of this data must be broken apart to
form the original records that GEOS expects.
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F ASCII
----------------------------------------------- ----------------
02F0: .. .. .. .. .. .. .. .. .. .. A9 00 8D EE 04 A4 ..........©ú<C2A9>î.¤
0300: FE B9 86 84 30 06 29 0F C9 02 D0 12 A4 70 B9 86 þ¹†„0.).É.Ð.¤p¹†
0310: 84 30 06 29 0F C9 02 D0 05 A9 07 8D A0 1D 20 1E „0.).É.Ð.©.<2E> .ú.
0320: 23 20 04 1A 8A D0 20 20 12 1A 18 A9 00 6D F4 03 #ú..ŠÐúú...©úmô.
0330: 8D F4 03 A9 03 6D F5 03 8D F5 03 20 C5 22 20 7C <20>ô.©.mõ.<2E>õ.úÅ"ú|
0340: 1B 20 04 1A 20 6B 1A A9 08 8D A0 1D B8 50 53 8D .ú..úk.©.<2E> .¸PS<50>
0350: EE 04 20 12 1A A2 00 A4 70 20 3F 24 C9 04 B0 3F î.ú..¢ú¤pú?$É.°?
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