6502	A80	ARM	PDP11	32016	80x86	On entry:	On exit:
A	A	R0	R0	R1	AL	function code	object type or preserved if function unsupported
XY	HL		R1		BX	control block	preserved, control block updated
		R1		R2		pointer to filename	preserved
		R2		R3		Load Address	Load Address
		R3		R4		Execution Address	Execution Address
		R4		R5		Start Address	Length
		R5		R6		End Address or Attributes	Attributes

Control block:
&00	Address of filename
&02	Load Address
&06	Execution Address
&0A	Length, or start address for SAVE and CREATE
&0E	Attributes, or end address for SAVE and CREATE

Function
&FD	Read file system information (System Internal Name)
&FE	Verify file
&FF	Load file
0	Save file
1	Write load, exec, attrs
2	Write load address
3	Write execution address
4	Write attributes
5	Read object information
6	Delete object
7	Create empty file
8	Create a directory

Object types returned in A are:
&FF	Execute-only file
&00	Object not found
&01	File found
&02	Directory found
&03	Image file found (file accessible as a directory)
&04	Unresolved symbolic link found
Note: The Tube protocol masks off bit 7 of the return value from OSFILE, so A=&FF is returned as A=&7F.

File attributes. These are held in four bytes as follows:
Byte &0E	bit 7	Private
	bit 6	Executable by others
	bit 5	Writable by others
	bit 4	Readable by others
	bit 3	Locked
	bit 2	Executable only by owner
	bit 1	Writable by owner
	bit 0	Readable by owner
Byte &0F	bits 0-4	Date: day of month
	bits 5-7	Date: year since 1981, bits 4-6
Byte &10	bits 0-3	Date: month of year
	bits 4-7	Date: year since 1981, bits 0-3
Byte &11	bits 0-7	Undefined (returned as zero)
See also File Access

Functions
&FD	Read file system information. The attributes field is returned holding the sector start address.
&FE	Verifies a file. The control block is as for A=&FF, LOAD. If the verification is successful, A is returned holding &01 and the control block holds the file information, as with function call &05. If the verification fails, A is returned holding &00 and the load address is returned holding the address where the verification failed. If the file does not exist or is a directory or does not have read access, then an error is generated.
&FF	Loads a file into memory. If the low byte of the execution address is zero, the file's own load address is used, otherwise the supplied address is used to load to. If the filename does not exist, or is a directory, or an execute-only file, or does not have read access, then an error is generated.
&00	Saves a file. If a file already exists with the same name, it is overwritten, with the file access and the case of the name staying the same. If the file is locked, or a directory exists with the same name, or the file is open, then an error is generated.
&01	Write an object's reload address, execution address and attributes.
&02	Write an object's reload address.
&03	Write an object's execution address.
&04	Write an object's attributes.
&05	Read object's catalogue information into the control block.
&06	Delete object. If the object does not exist, A returned as &00. If the object is locked, or is not owned, or is a directory that is not empty, or is open, then an error is generated.
&07	Create an empty file of defined length. Block as for SAVE. The supplied start address is usually passed as &0 and the end address as the required length. No data is transfered, and the file does not necessarily contain zeros. Some file systems may deliberately overwrite any existing data in the file. If a file already exists with the same name, it is overwritten, with the file access and the case of the name staying the same. If the file is locked, or a directory exists with the same name, or the file is open, then an error is generated.
&08	Create a directory. The length field is passed holding a suggested minimum number of entries required, or zero for a default number. If a directory already exists, there is no error. The created directory is locked. If a file already exists, an error is generated.

Calling from BBC BASIC

Entry points