OSGBPB

Read or write multiple bytes of data

Specification

6502	Z80	6809	PDP11	80x86	32016	ARM	On entry:	On exit:
A	A	A	R0	AL	R1	R0	= function code	= &00 if supported, preserved if not supported, but see notes.
XY	HL	X	R1	BX			=>control block	undefined
Control block
&00					R2	R1	Handle	Cycle number
&01					R3	R2	Data address	Updated Data address
&05					R4	R3	Number of bytes or objects to transfer	Updated Number of bytes or objects
&09					R5	R4	Pointer to use for transfer	Updated Pointer
&0D
								Cy=EOF status (but see notes)

Functions
&01	Write bytes to media using new pointer.
&02	Write bytes to media ignoring new pointer.
&03	Read bytes from media using new pointer.
&04	Read bytes from media ignoring new pointer.
With functions &01 and &03 the PTR is first set to the supplied value before transferring data. On exit the number of bytes actually transferred is subtracted from the 'number of bytes' field and added to the 'data address' field and the PTR. The new PTR is returned in the 'PTR' field. The carry flag is returned set if the 'number of bytes' field is not zero on exit -- meaning a read was attempted past EOF. If the read or write extended past end-of-file the EOF error-flag is set and a further read without changing PTR will cause an EOF error. If a write extends past EOF the file is extended, however the contents of the new part of the file are undefined unless overwritten. An error occurs if the object is not a file or does not have the correct access. If the handle is 0, action is undefined. Some systems allow multiple bytes to be written to OSWRCH or read from OSRDCH if the handle is 0.
&05	Get media title of CSD disk and boot option into data block: &00         length of title (n) &01         title in ASCII characters &01+n     startup option &02+n     drive number &03+n
&06	Get currently selected directory name into data block: &00         length of drive identity (n) &01         ASCII drive identity (drive number) &01+n     length of directory name (m) &02+n     directory name in ASCII characters &02+n+m ownership: &00 - owner, &FF - public &03+n+m
&07	Get current library name into data block: &00         length of drive identity (n) &01         ASCII drive identity (drive number) &01+n     length of library name (m) &02+n     library name in ASCII characters &02+n+m ownership: &00 - owner, &FF - public &03+n+m
&08	Read filenames from current directory into data block: &00         length of filename 1 (n) &01         filename 1 in ASCII characters &01+n     length of filename 2 (m) &02+n     filename 2 in ASCII characters &02+n+m etc... The first call to function &08 should be made with the transfer pointer set to zero. This will read the first filename, and the pointer will be updated so that the next call will read the next filename. The cycle number of the current directory is also returned in XY+0. When no filenames are left, the call returns with the 'number of filenames' greater than zero and the carry flag set.
&09	Reads work/login filename, command line tail or entries from specified directory. If the handle is zero, reads work/login filename or command tail: &00         length of drive identity or command line tail (n) &01         ASCII drive identity (drive number) or comand line tail &01+n     length of work/login filename (m) &02+n     work/login filename &02+n+m If the handle is a channel number of an open directory, reads a null-terminated list of directory entries. The function is called as for OSGBPB 8, but the updated number of objects is the number of filenames read.
&0A	Read entries and information from the opened directory whose channel number is passed in the handle. This function is called as for OSGBPB 9. Each record is a whole multiple of four bytes long: &00 Load address &04 Execution address &08 Length &0C Attributes &10 Object type (1=file, 2=directory, 3=image file, 4=unresolved symbolic link) &14 Object name, null terminated xxx next record
&0B	Read entries and information from the opened directory whose channel number is passed in the handle. This function is called as for OSGBPB 9. Each record is a whole multiple of four bytes long: &00 Load address &04 Execution address &08 Length &0C Attributes &10 Object type (1=file, 2=directory, 3=image file, 4=unresolved symbolic link) &14 Sector start address &18 Five zeros or centisecond time since 1900 &1D Object name, null terminated xxx next record
&0C	Read entries and information from the opened directory whose channel number is passed in the handle. This function is called as for OSGBPB 9. Each record is a whole multiple of four bytes long: &00 Load address &04 Execution address &08 Length &0C Attributes &10 Object type (1=file, 2=directory, 3=image file, 4=unresolved symbolic link) &14 Object file type (b8-b19 of load address) &18 Object name, null terminated xxx next record

Notes

Some filing systems preserve A even if they support the function.

Many filing systems do not return Carry consistently. The only consistent way of telling if the end of file has been reached is to test whether the updated number of bytes/objects is unequal to zero.

Calling from BBC BASIC

BBC BASIC makes no calls to OSGBPB.

Entry points

• BBC BASIC Entry Address: &FFD1
• 6502 Entry Address: &FFD1, vectors via &021A
• Z80 Entry Address: &FFD1, vectors via &FFD2
• 6809 Entry Address: &FFD1, vectors via &FFD2
• 80x86 Entry Address: INT &41, vectors via 0000:0104
• 32000 Entry Address: SVC &0F
• PDP-11 Entry Address: EMT 11, vector &0B
• ARM Entry Address: SWI &0C "OS_GBPB", vector &0C

Implementations

CFS

Not implemented, simply returns with an RTS instruction.

The Master 128 implements &02 and &04.

ROMFS

Not implemented, simply returns with an RTS instruction.

The Master 128 implements &04.

DFS

Acorn DFS and contemporary filing systems implement functions &01 to &08 inclusive. Watford DFS implements &09 to read the work name.

ADFS

ADFS implements &01 to &08

HADFS

HADFS implements &01 to &0B.

Z80Tube

The Z80Tube Z80 emulator implements OSGBPB 9,0 to read the command line tail.

Jgharston 17:01, 6 November 2009 (UTC)