6502Em

The Filing System

The emulator provides a full filing system by means of the VDFS ROM.

The following commands can be used to select the Virtual DFS ROM as the current filing system:

*DISC
*DISK
*ADFS
*FADFS

In addition, the following commands are offered:

*Quit      (Return to the desktop)
*Desktop   (Return to the desktop)
*Shadow    (dummy command)
*SRLoad    (load image into sideways RAM)
*SRWrite   (copy memory into sideways RAM)

ImageDFS and 6502Em

ImageDFS is also available from Warm Silence Software.

Partial emulation of OSWORD &72 and &7F is performed by 6502Em.

A much fuller implementation of OSWORD &7F is offered by ImageDFS.

Even if ImageDFS is not loaded, *DRIVE assumes that you are running from a DFS disc that has been copied to ADFS. So for example *DRIVE 2 will attempt to change to the directory 'DFSSide2'.

However if ImageDFS is loaded, *DRIVE <n> will change directory to access a physical floppy drive unless a DFSImage has been dropped onto 6502Em's icon, in which case it will behave as above.

To access a physical floppy drive if ImageDFS is now loaded, *Mount <n> should be used.

Changing Directory

The DFS filing system structure is fully emulated by noticing when an ADFS directory's name is one letter long.

eg if your Currently Selected Directory (CSD) is ADFS::HD.$.BBC.Games.J then:

• *DIR K will attempt to set the CSD to ADFS::HD.$.BBC.Games.K
• *DIR J will leave the CSD unaltered
• *DIR $ will set the CSD to ADFS::HD.$.BBC.Games (to change to the "real" root directory, use *DIR :4.$)
• *DIR ^ will set the CSD to ADFS::HD.$.BBC.Games

eg if your CSD is ADFS::HD.$.BBC.Games then:

• *DIR $ will leave the CSD unchanged
• *DIR ^ will set the CSD to ADFS::HD.$.BBC

If your CSD is set to, for example, ADFS::HD.$.BBC.G.L then ambiguity can arise, so single letter directories should NOT be used within each other.

Drive numbers within filenames (eg :0.E.Jameson) are ignored so that you can save positions of games onto your hard disc.

To specify a drive, use ADFS::0.Jameson

*Drive does not behave as expected (see above) so to change drive use *Mount 0, *DIR :0, *DIR ADFS::0, *DIR ADFS::HD etc

RISC OS's CSD is not changed by the emulator, allowing several incarnations of the emulator to be active.

Some filing systems (eg DOSFS) do not support OSGBPB 8, so programs that use it will not work on such filing systems.

OSFSC, OSFIND, OSGBPB, OSBPUT, OSBGET, OSARGS, OSFILE are all fully supported.

In addition, OSGBPB 9 is partially supported (for the current directory):

block?0=number of files to read (number of files read)
block!1=address in memory of data
block!5=length of data block
block!9=sequential pointer (0 for first call, -1 when finished)

RISC OS errors are passed back into the emulator via BRK.

Filing system operations appear instantaneous to the emulator (ie do not run filing system benchmarks within the emulator!)

Although the operating system normally appears to be ROM, it can be overwritten by filing system calls (eg *Load)

Files that will extend beyond &FFFF will generate an error if you try to load them. (normally files might wrap round back to &0000)