OSGBPB

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
YX	HL	X	R1	BX			=>control block	undefined, control block updated
Control block
&00					R2	R1	Handle	Cycle Number
&01					R3	R2	Data Address	Updated Data Address
&05					R4	R3	Count	Updated Count
&09					R5	R4	Offset	Updated Offset
&0D								Cy=EOF but see notes

Function summary
&01	Write bytes to open file using new pointer
&02	Write bytes to open file ignoring new pointer
&03	Read bytes from open file using new pointer
&04	Read bytes from open file ignoring new pointer
&05	Read media title and boot option of CSD disk
&06	Read name of current directory
&07	Read name of current library
&08	Read object names from current directory
&09	Read object names from directory, work/login filename, command line tail
&0A	Read object names and information from directory
&0B	Read object names and extended information from directory
&0C	Read object names and filetype information from directory

Functions

&01	Write bytes to open file using new pointer.
&02	Write bytes to open file ignoring new pointer.
&03	Read bytes from open file using new pointer.
&04	Read bytes from open file 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 returned in the 'number of bytes' field the number of bytes actually transfered is 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, the action is undefined. Some systems allow multiple bytes to be written to OSWRCH or read from OSRDCH if the handle is 0.
&05	Read title and boot option of CSD disk into data block: &00         length of title (n) &01         title in ASCII characters &01+n     startup option &02+n     drive number &03+n
&06	Read 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	Read 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 object names 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 object names from directory, work/login filename, command line tail: Reading object names: &00         object name, null terminated xxx         next record Reading work/login filename or command line 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. See also implementation notes
&0A	Read object names and information from the opened directory whose channel number is passed in the handle. If the channel is zero the current directory is scanned. 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, padded to four bytes xxx next record
&0B	Read object names and extended information from the opened directory whose channel number is passed in the handle. If the channel is zero the current directory is scanned. 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, padded to four bytes xxx next record
&0C	Read object names and filetype information from the opened directory whose channel number is passed in the handle. If the channel is zero the current directory is scanned. 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, padded to four bytes 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.

In Opus EDOS and Slogger Challenger, OSGBPB 5 does not return the CSD drive number. In Opus DDOS the drive number byte includes a representation of the volume letter in bits 6..4.

In Opus/Slogger filing systems the drive identity returned by OSGBPB 6 and 7 consists of one or two characters, the first being the ASCII drive digit 0..3 and the second being the optional volume letter A..H.

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.

65Tube

The emulator traps implemented in 65Tube allows calls to OSGBPB with A>9 to pass additional parameters:

On entry:		On exit:
XY?0	= ignored	XY?0	= directory cycle
XY!1	= address	XY!1	= updated address
XY!5	= count	XY!5	= returned count
XY!9	= offset	XY!9	= updated offset
XY!13	=>directory name	XY!13	= preserved
XY!17	=>wildcard to match	XY!17	= preserved

6502Em

The emulator traps implemented in Warm Silence's 6502Em implement OSGBPB 9 to read object names from the current directory, but use the control block contents differently from the standard:

On entry:		On exit:
XY?0	= count	XY?0	= returned count
XY!1	= address	XY!1	= preserved
XY!5	= buffer length	XY!5	= preserved
XY!9	= offset	XY!9	= updated offset

Jgharston 17:01, 6 November 2009 (UTC) Jgharston (talk) 15:56, 30 September 2016 (UTC) Jgharston (talk) 00:03, 3 October 2016 (UTC)