Int 45  - Acorn Bbc Master 512 - "osfile" - Read/write File Or Directory   [O]

   AL = function
       00h save block of memory as file
       01h update directory entry for existing file
       02h set load address for existing file
       03h set execution address for existing file
       04h set attributes for existing file
       05h read directory
       06h delete file
       FFh load file
   DS:BX -> control block (see below)

Return: FLAGS destroyed
   AL = file type
       00h not found
       01h file found
       02h directory found
       FFh protected file

See Also: INT 40"Acorn",INT 41"Acorn",INT 44"Acorn",INT 46"Acorn"

Format of control block:
Offset Size    Description
 00h   WORD    address of CR-terminated filename
 02h   DWORD   load address of file
 06h   DWORD   execution address of file
 0Ah   DWORD   start address of data to save
 0Eh   DWORD   end address of data to save, or file attributes
       file attributes in low byte (see below)
       other three bytes are filing-system specific file attributes

Bitfields for file attributes:
 bit 0 no owner read access
 bit 1 no owner write access
 bit 2 not executable by owner
 bit 3 not deletable by owner
 bit 4 no public read access
 bit 5 no public write access
 bit 6 not executable with public access
 bit 7 not deletable with public access