Since the Z380 only outputs the memory select signal UMCS within the first 16 MB of memory, and I wanted to keep things simple, I decided 16 MB of RAM was sufficient. It's still possible to add more memory, of any kind, but you will have to decode it yourself, because the MPU decodes nothing above 16 MB.
The original NAS-SYS 3 monitor has been adapted for the requirements of the Z380 extended mode. Some of the old commands still exist, like Copy, Modify and Tabulate, while old ones, like reading and writing of cassette tapes, have been removed. The command line editing facilities have been enhanced, and it is possible to use all eight video pages present on today's video cards.
In the siux system there is no video RAM, no keyboard, no floppy or hard disk controllers, and hence no file system. Instead, these components have been replaced by the information stream a server program, executed by the PC, provides.
Information exchange between the PC and the card takes place over the parallel port on the PC and the EPP controller PLD on the card. The data rate is high enough as to make the communication completely transparent to the user, at least as far as house keeping I/O is concerned. Loading of extremely large files will of course take some time to finish.
The good old NASCOM debugger and disassembler have been combined into one executable file: a symbolic debugger. It allows code to be debugged anywhere in the 32 bit address space. Many of the original commands have been kept and many new commands have been added.
The debugger supports
- an alternate video page for programs that use the screen
- switching of siux's workspace variables for programs that use that workspace
- an extended single step display showing register contents in the selected register set
- multiple breakpoints, breakpoint counting and CPU register supervision
- symbolic mode in which breakpoints can be assigned numerically or symbolically
- command sequences can be stored in a text file and be replayed as a macro by pressing alt+key
There is still another important software component in this system. It's the Exec overlay which is loaded when the system boots. Exec.go is for siux what command.com is for msdos. Exec allows you to load and save files on the PC, and to start executables just like on any computer. In appearance it's still a NASCOM with PolyDos.
One of the most useful features in the PolyDos system is its ability to enter command file mode, in which characters are fetched from a file instead of the keyboard. When the file is exhausted, command file mode ends and input from the keyboard is resumed. This feature has been enhanced in several ways. First and most important, command files can be nested to any reasonable depth. Second, a new command file type has been added. Instead of keeping numerous command files in the working directory, it is also possible to keep all of them in a single file thus making command file administration easy and the working directory clean. The Exec overlay sees to that the command file block name is located and the command file gets started.
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