Difference between revisions of "AMSDOS Header"
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|- | |- | ||
| − | ! Size !! Name !! Notes | + | ! Offset !! Size !! Name !! Notes |
|- | |- | ||
| − | | BYTE || User number || 0-15, or #E5 for deleted entries | + | | 0 || BYTE || User number || 0-15, or #E5 for deleted entries |
|- | |- | ||
| − | | 8 BYTES || Filename || Unused characters are filled with space | + | | 1 || 8 BYTES || Filename || Unused characters are filled with space |
|- | |- | ||
| − | | 3 BYTES || Extension || Unused characters are filled with space | + | | 9 || 3 BYTES || Extension || Unused characters are filled with space |
|- | |- | ||
| − | | DWORD || Zero || Contains all zeroes | + | | C || DWORD || Zero || Contains all zeroes |
|- | |- | ||
| − | | BYTE || Block number || Tape only | + | | E || BYTE || Block number || Tape only |
|- | |- | ||
| − | | BYTE || Last block || Tape only | + | | F || BYTE || Last block || Tape only |
|- | |- | ||
| − | | BYTE || File type || 0:BASIC 1:Protected 2:Binary (ASCII files don't have headers but a fake header is built in memory with the file type #16, "Unprotected ASCII v1") | + | | 10 || BYTE || File type || 0:BASIC 1:Protected 2:Binary (ASCII files don't have headers but a fake header is built in memory with the file type #16, "Unprotected ASCII v1") |
|- | |- | ||
| − | | WORD || Data location || Address of the 2KB buffer | + | | 11 || WORD || Data location || Address of the 2KB buffer |
|- | |- | ||
| − | | WORD ||Load address || | + | | 13 || WORD ||Load address || |
|- | |- | ||
| − | | BYTE || First block || Set to #FF, only used for output files | + | | 14 || BYTE || First block || Set to #FF, only used for output files |
|- | |- | ||
| − | | WORD ||style="white-space: nowrap;"| Logical length || Actual file length is here | + | | 15 || WORD ||style="white-space: nowrap;"| Logical length || Actual file length is here |
|- | |- | ||
| − | | WORD || Entry address || | + | | 17 || WORD || Entry address || |
|- | |- | ||
| − | | 36 BYTES || Unused || | + | | 19 || 36 BYTES || Unused || |
|- | |- | ||
| − | | 3 BYTES || Real length || 24-bit number. Just a copy, not used! | + | | 3D || 3 BYTES || Real length || 24-bit number. Just a copy, not used! |
|- | |- | ||
| − | | WORD || Checksum || Unsigned sum of all bytes until this field | + | | 40 || WORD || Checksum || Unsigned sum of all bytes until this field |
|- | |- | ||
| − | | | + | | 42 || 59 BYTES || Unused || Free to use |
|} | |} | ||
Revision as of 14:44, 7 November 2023
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:
| Offset | Size | Name | Notes |
|---|---|---|---|
| 0 | BYTE | User number | 0-15, or #E5 for deleted entries |
| 1 | 8 BYTES | Filename | Unused characters are filled with space |
| 9 | 3 BYTES | Extension | Unused characters are filled with space |
| C | DWORD | Zero | Contains all zeroes |
| E | BYTE | Block number | Tape only |
| F | BYTE | Last block | Tape only |
| 10 | BYTE | File type | 0:BASIC 1:Protected 2:Binary (ASCII files don't have headers but a fake header is built in memory with the file type #16, "Unprotected ASCII v1") |
| 11 | WORD | Data location | Address of the 2KB buffer |
| 13 | WORD | Load address | |
| 14 | BYTE | First block | Set to #FF, only used for output files |
| 15 | WORD | Logical length | Actual file length is here |
| 17 | WORD | Entry address | |
| 19 | 36 BYTES | Unused | |
| 3D | 3 BYTES | Real length | 24-bit number. Just a copy, not used! |
| 40 | WORD | Checksum | Unsigned sum of all bytes until this field |
| 42 | 59 BYTES | Unused | Free to use |
To calculate the checksum just add all bytes from 00 up to and including byte 66 together.
This is only a summary. All details are in Firmware Guide chapter 9, page 4.
