Difference between revisions of "AMSDOS Header"
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{| class="wikitable" | {| class="wikitable" | ||
|- | |- | ||
− | ! Bytes !! Name !! Notes | + | ! Field !! Bytes !! Name !! Notes |
|- | |- | ||
− | | 0 || User number || 0-15, or #E5 for deleted entries | + | | rowspan="10" | System || 0 || User number || 0-15, or #E5 for deleted entries |
|- | |- | ||
| 1..8 || Filename || Unused characters are filled with space | | 1..8 || Filename || Unused characters are filled with space | ||
Line 17: | Line 17: | ||
| 17 || Last block || Tape only, set to 0 | | 17 || Last block || Tape only, set to 0 | ||
|- | |- | ||
− | | 18 || File type || Bit0 = Protection (set if protected) | + | | 18 || File type || As per cassette: Bit0 = Protection (set if protected) |
Bits1..3 = File contents (0:BASIC, 1:Binary, 2:Screen image, 3:ASCII, 4..7 are unallocated) | Bits1..3 = File contents (0:BASIC, 1:Binary, 2:Screen image, 3:ASCII, 4..7 are unallocated) | ||
Line 23: | Line 23: | ||
Bits4..7 = Version (ASCII files should be version 1, all other files should be version 0) | Bits4..7 = Version (ASCII files should be version 1, all other files should be version 0) | ||
|- | |- | ||
− | | 19..20 || Data length || | + | | 19..20 || Data length || As per cassette: the number of data bytes in the data record |
|- | |- | ||
− | | 21..22 || Data location || | + | | 21..22 || Data location || As per cassette: where the data was written from originally |
|- | |- | ||
| 23 || First block || Set to #FF, only used for output files | | 23 || First block || Set to #FF, only used for output files | ||
|- | |- | ||
− | | 24..25 || Logical length || | + | | rowspan="3" | User || 24..25 || Logical length || As per cassette: actual file length is here |
|- | |- | ||
− | | 26..27 || Entry address || | + | | 26..27 || Entry address || As per cassette: the execution address for machine code programs |
|- | |- | ||
| 28..63 || Unused || As per cassette | | 28..63 || Unused || As per cassette | ||
|- | |- | ||
− | | 64..66 || Real length || Length of the file in bytes, excluding the header record. 24 bit number, least significant byte first. Just a copy, not used! | + | | rowspan="3" | AMSDOS || 64..66 || Real length || Length of the file in bytes, excluding the header record. 24 bit number, least significant byte first. Just a copy, not used! |
|- | |- | ||
| 67..68 || Checksum || Unsigned sum of all bytes until this field | | 67..68 || Checksum || Unsigned sum of all bytes until this field | ||
Line 41: | Line 41: | ||
| 69..127 || Unused || | | 69..127 || Unused || | ||
|} | |} | ||
+ | |||
+ | |||
These headers are detected by checksumming the first 67 bytes of the record. If the checksum is as expected then a header is present, if not then there is no header. | These headers are detected by checksumming the first 67 bytes of the record. If the checksum is as expected then a header is present, if not then there is no header. | ||
− | + | When a file without a header is opened for input, a fake header is constructed in store as follows: | |
+ | |||
+ | {| class="wikitable" | ||
+ | |- | ||
+ | ! Bytes !! Name !! Notes | ||
+ | |- | ||
+ | | 0 || User number || User number, #00..#FF | ||
+ | |- | ||
+ | | 1..8 || Filename || Unused characters are filled with space | ||
+ | |- | ||
+ | | 9..11 || Extension || Unused characters are filled with space | ||
+ | |- | ||
+ | | 12..15 || Zero || Contains all zeroes | ||
+ | |- | ||
+ | | 18 || File type || #16, unprotected ASCII version 1 | ||
+ | |- | ||
+ | | 19..20 || Data location || Address of 2K buffer | ||
+ | |- | ||
+ | | 23 || First block || Set to #FF | ||
+ | |} | ||
+ | |||
+ | All other fields are set to zero. | ||
This is only a summary. All details are in [[Firmware Guide]] chapter 9, page 4. | This is only a summary. All details are in [[Firmware Guide]] chapter 9, page 4. | ||
+ | |||
+ | === Expansion of the AMSDOS Header === | ||
+ | Some OS and DOS expanded the classic AMSDOS header: | ||
+ | |||
+ | 1. [[FutureOS Header]]: | ||
+ | * Contains and icon or information text | ||
+ | * File length is 24 Bit | ||
+ | * Defined Loading and Autostart (expansion) RAM configuration | ||
+ | * Additional file types | ||
[[Category:Disc Operating System]] | [[Category:Disc Operating System]] | ||
[[Category:Programming]] | [[Category:Programming]] |
Latest revision as of 07:34, 24 October 2024
In AMSDOS it is possible to store files in two ways: headerless and with a header. Headerless files are often files which were created with OPENOUT and SAVE"filename",a. Programs normally have a file header, which consist of 128 bytes and contain the following data:
Field | Bytes | Name | Notes |
---|---|---|---|
System | 0 | User number | 0-15, or #E5 for deleted entries |
1..8 | Filename | Unused characters are filled with space | |
9..11 | Extension | Unused characters are filled with space | |
12..15 | Zero | Contains all zeroes | |
16 | Block number | Tape only, set to 0 | |
17 | Last block | Tape only, set to 0 | |
18 | File type | As per cassette: Bit0 = Protection (set if protected)
Bits1..3 = File contents (0:BASIC, 1:Binary, 2:Screen image, 3:ASCII, 4..7 are unallocated) Bits4..7 = Version (ASCII files should be version 1, all other files should be version 0) | |
19..20 | Data length | As per cassette: the number of data bytes in the data record | |
21..22 | Data location | As per cassette: where the data was written from originally | |
23 | First block | Set to #FF, only used for output files | |
User | 24..25 | Logical length | As per cassette: actual file length is here |
26..27 | Entry address | As per cassette: the execution address for machine code programs | |
28..63 | Unused | As per cassette | |
AMSDOS | 64..66 | Real length | Length of the file in bytes, excluding the header record. 24 bit number, least significant byte first. Just a copy, not used! |
67..68 | Checksum | Unsigned sum of all bytes until this field | |
69..127 | Unused |
These headers are detected by checksumming the first 67 bytes of the record. If the checksum is as expected then a header is present, if not then there is no header.
When a file without a header is opened for input, a fake header is constructed in store as follows:
Bytes | Name | Notes |
---|---|---|
0 | User number | User number, #00..#FF |
1..8 | Filename | Unused characters are filled with space |
9..11 | Extension | Unused characters are filled with space |
12..15 | Zero | Contains all zeroes |
18 | File type | #16, unprotected ASCII version 1 |
19..20 | Data location | Address of 2K buffer |
23 | First block | Set to #FF |
All other fields are set to zero.
This is only a summary. All details are in Firmware Guide chapter 9, page 4.
Expansion of the AMSDOS Header
Some OS and DOS expanded the classic AMSDOS header:
1. FutureOS Header:
- Contains and icon or information text
- File length is 24 Bit
- Defined Loading and Autostart (expansion) RAM configuration
- Additional file types