OSARGS
Contents
Specification
| 6502 | Z80 | 6809 | PDP11 | 80x86 | 32016 | ARM | 68000 | RISC-V | On entry: | On exit: |
| A | A | A | R0 | AL | R1 | R0 | D0 | A0 | = function code | preserved if not supported, but see notes. |
| Y | E | Y | R1 | AH | R2 | R1 | D1 | A1 | = file handle or 0 | preserved |
| X | =>four-byte data word in zero page | preserved, data word updated | ||||||||
| HL | X | R2 | BX | =>four-byte data word | preserved, data word updated | |||||
| R3 | R2 | D2 | A2 | = four-byte data word | any returned four-byte data word |
If the data word is not used, then it is ignored and so X/HL/R2/BX/R3/R2/D2/A2 may be left set to anything on entry.
| Functions | handle<>0 | handle=0 |
| &80 | Read file handle internal info | |
| &FD | Write context | Return version and capabilities |
| &FE | Read context | Return last drive used |
| &FF | Ensure open file to media | Ensure all open files to media |
| &00 | Read PTR | Read filing system number |
| &01 | Write PTR | Read address of command tail |
| &02 | Read EXT | Read NFS version |
| &03 | Write EXT | Read libfs number |
| &04 | Read size allocated to file | Read disk space used |
| &05 | Read EOF | Read disk free space |
| &06 | Ensure file size of open file | |
| &07 | Convert file handle to filename | |
| &08 | Inform change in image filestamp |
Functions, handle<>0
| &00 | Reads the sequential pointer of the open object. |
| &01 | Writes the sequential pointer of the pen file. If PTR is moved past the end of an output file, the file is extended with zeroes and zero returned in A, otherwise A = &FF on exit. Some filing systems do not write zeroes; the contents of the new part of the file are undefined. If PTR is moved past the end of an input file, an error is generated. The EOF-error-flag is cleared. The PTR of an open directory cannot be written. |
| &02 | Reads the extent of the open object. |
| &03 | Writes the extent of the open object. If the length of the file is reduced, the end disappears. If the length is increased, the file is extended as with function &01 and zero is returned in A, otherwise A = &FF on exit. The EOF-error-flag is cleared. The EXT of an open directory cannot be written. |
| &04 | Reads the space allocated to the open object. This will be at least the current extent of the object, and determines how many more bytes can be written to the object before the object has to be extended or the write fails with a "Can't extend" error. |
| &05 | Reads the EOF for the open object. If PTR=EXT then &FFFFFFFF is returned, otherwise 0 is returned. |
| &06 | Ensures the open file is allocated the specified amount of space. Returns the actual amount of space allocated. |
| &07 | Convert file handle to filename (RISC OS).
The data word in R2 points to a buffer, the size of which is given in R5. On exit, the data word in R2 is preserved, the buffer contains the filename as a NUL-terminated string, and R5 is decreased by the number of characters in the filename excluding the NUL. The NUL is addressed by R2 + R5entry - R5exit. |
| &08 | Inform the underlying file system of new image stamp in data word. |
| &80 | Read information on handle. Returns four bytes of data:
|
| &FD | Write filing system context. HADFS implements:
|
| &FE | Read filing system context. HADFS implements:
RISC OS: Returns the filing system information word in the data word and the stream information for the handle in A or R0. On 8-bit systems only the bottom 8 bits of the stream information word will be returned.
|
| &FF | Ensures any buffered data for the open file is written to the media. |
Functions, handle=0
| &00 | Return filing system number in A:
0 No current filing system 20 RawKbd: 1 1200 baud cassette filing system 21 DeskFS: 2 300 baud cassette filing system 22 Computer Concepts RomFS: 3 ROM filing system 23 RamFS: 4 Disk filing system 24 RISCiXFS: 5 Econet network filing system 25 Streamer: 6 Teletext/Prestel telesoftware 26 SCSIFS: 7 IEEE filing system 27 Digitiser: 8 Acorn ADFS 28 Scanner: 9 Host filing system 29 MultiFS: 10 Videodisk filing system 11 33 NFS: 12 RAM filing system NetPrint: 37 CDFS: 13 Null: 43 DOSFS: 14 Printer: 46 ResourceFS: 15 Serial: 47 PipeFS: 16 Harston ADFS 17 Vdu: 53 DeviceFS: 18 RawVdu: 54 Parallel: 19 Kbd: |
| &01 | Returns the address of the command line tail, any parameters after a filename. The character at the address is the first non-space character after the name of the command (for example the 2 in *FORM80 2.) The address will always be in the I/O processor. |
| &02 | Returns A=0 for ANFS 4.00+, A=1 if later bug-fixed versions of NFS, returns A=2 if early bug-ridden NFS or if call unsupported. |
| &03 | Returns libfs filing system number in A. |
| &04 | Returns used space on the device with the currently selected directory on. |
| &05 | Returns free space on the device with the currently selected directory on. |
| &FD | Returns version number*10 in BCD in A and filing system capability flags in the data word. |
| &FE | Returns the last drive accessed in the data word. |
| &FF | Ensures any buffered data for all open files is written to the media. |
Calling from BBC BASIC
-
ptr=PTR#chcalls OSARGS 0,ch -
PTR#chn=ptrcalls OSARGS 1,ch -
ptr=EXT#chcalls OSARGS 2,ch -
EXT#ch=ptrcalls OSARGS 3,ch -
=EOF#chcalls OSBYTE 127 on 8-bit systems, which vectors via FSCV. Otherwise,=EOF#chcalls OSARGS 5,ch.
Special handles
When reading PTR and EXT from 8-bit BASIC, the data parameter is BASIC's integer store, which will be set to the channel as the last item evaluated. That means that PTR#0 and EXT#0 pass a data value of zero; OSARGS 0,0 and OSARGS 2,0 do not change the data word; this means that in 8-bit BASICs PTR#0 and EXT#0 return zero, being the unchanged data word set to the channel.
This means that other BASIC have the ability to use PTR#0 and EXT#0 to return information specific to that implementation. Some BASICs or operating systems allow other special handles to return specific information. Some operating systems allow BPUT#0 and BGET#0 to access the VDU and keyboard, so allow PTR#0, EXT#0 and EOF#0 to access keyboard or VDU information.
See Special handles.
Entry points
- BBC BASIC Entry Address: &FFDA
- 6502 Entry Address: &FFDA, vectors via &0214
- Z80 Entry Address: &FFDA, vectors via &FFDB
- 6809 Entry Address: &FFDA, vectors via &FFDB
- 80x86 Entry Address: INT &44, vectors via 0000:0110
- 32000 Entry Address: SVC &0C
- PDP-11 Entry Address: EMT 8, vector &08
- ARM Entry Address: SWI &09 "OS_Args", vector &09
- 68000 Entry Address: MOV #&09,A0:TRAP 12
- RISC-V Entry Address: ECALL &AC0008
Implementations
CFS
Not implemented, simply returns with an RTS instruction.
The Master 128 implements &00 fully, and &01 with a handle of 0.
ROMFS
Not implemented, simply returns with an RTS instruction.
The Master 128 implements &00 fully, and &01 with a handle of 0.
DFS
Acorn DFS 0.xx and 1.xx implements &FF to &02. DFS 2.xx and later also implements &03.
HDFS
Andrew Duggan's Hierarchial DFS implements OSARGS &03,Y as 'Read allocated space' instead of 'Write extent'.
Watford DFS
Implements &FE to &02. OSARGS &FE preserves A, so the returned data has to be examined to see if the call has been acted on with code such as:
drive%=FNargs(&FE,-1)AND&FF
drive% will be &FF if not supported, or the drive number if it is.
NFS
NFS 3.34 returns the command line address incorrectly. It points to the first non-'*' character of the command, not the first character of the parameters. NFS 3.60 and later return the command line address correctly. NFS 3.60 and later return A<>2 from OSARGS 2,0 to indicate this.
ADFS
HADFS
Implements &FD to &06.
Sprow ARM7 CoPro
When reading the current filing system with OS_Args all three parameters
must be zero, including the data parameter. SYS "OS_Args",0,0,data
does not return the filing system number unless data is zero. The data
parameter cannot be left set to a random value as it can when calling on other
platforms. ARM BBC BASIC translates calls to &FFDA correctly setting R2 to zero.
| Filing System Calls | |
|---|---|
