|★ APPLICATIONS ★ DIVERS ★ DOS USER DOS OR DOS USER DON'T USE ROMDOS? ★|
|Art Studio Loader for ROMDOS mk 2||Applications Divers|
OK. So you've got the Art Studio running with ROMDOS and you're enjoying the vast storage capacity of a ROMDOS format disk. “Yes, but when I catalogue the disk from the Art Studio it doesn't show all the screen files that I've saved!", I hear someone say. (Not me. Did you say anything, Adam? - Ed)
“Limited buffer size”, I reply, “What you need is a good dose of... User Area Relocation".
So let's get serious. When you select < Catalogue disc > from one of the Art Studio's Filing Menus, the relevant filenames, from the disk in the currently selected drive, are stored in an area of memory set aside for the purpose. Each filename is given a drive prefix (A: or B:) to aid identification. Catalogue a disk in the other drive and the new filenames will be added to those already in store.
With 178K capacity disks, this buffer is more than adequate, but add a 792K capacity disk (something which was not expected when the program was written) and it's quite possible to fill the buffer, and more besides. At best this will result in some files "disappearing" or at worst, cause a very nasty crash.
To avoid this potential disaster, we need to make use of USER AREAS. Not a popular subject, I know, probably due to the fact that they seem totally unnecessary when dealing with 178K capacity disks. But, with a possible 256 files on a D20 format (792K) disk, splitting the directory into manageable chunks makes a lot of sense. The problem is that the Art Studio does not have the facility to change from one User Area to another. Until now...
A little investigative work with a Multiface reveals that the Art Studio makes use of the firmware routine KM_READ_KEY (at &BB1B) to interrogate the keyboard when < Enter Filename > is selected from the Filing Menus. If we can intercept this routine then we can use it to enter a User Number instead of a filename, provided a “special" key is pressed first. And that is exactly what the poke below does. Use it to load the Art Studio instead of STUDIO.BAS and you will be able to select User Areas 0 to 9 as follows:-
All filing operations will use the selected User Area for both drives. Unfortunately the Art Studio does not display the currently selected User Area so it is up to you to exercise due care and attention when loading and saving files.
By Jess Harpur, Campursoft & WACCI
(Note, Jess is the UR in campURsft, Peter Campbell is the CAMP from CAMPursoft. If you're wondering where the soft comes from, that's easy as well, it's from all the ZX81 owners, they're all a bit soft.)