Creating new CP/M disk from scratch

Okay, here goes. This is how I'd do the whole process on my PC. First of all, I'd pick a disk format. Since you're limited to FM, you might as well use something with 128 bytes/sector and avoid having to write blocking/deblocking code. Another thing to think about is the interleave (physical or logical). I'd go with physical, since you can vary this without changing any code. If you're using a 4 MHz Z80 with that Versafloppy, 3:1 is a reasonable value to start with. 1:1 on slower CP/M systems generally only works when you can read and write a track at a time. However, there were darned few (if any) FM 5.25" formats that used physical interleaving (heaven only knows why). And very few 5.25" FM formats are double-sided (which I think that you'd really want, given the limited space on a FM 5.25" diskette. So you can either write your own 22DISK definition (easy enough) or use an existing one, say, the DSSD Cromemco CDOS one (22DISK CRO2) which will give you about 172K. First, I'm assuming that there's a PROM on the Versafloppy that will load the first sector of your floppy drive into RAM at some fixed location and jump to it. This first sector will contain your boot loader... Next, you need to write a boot loader, which basically sucks in the your CBIOS (see the next paragraph) and jumps to the cold boot entry to load the CP/M's DOS, which will, in turn, load CCP and give you a command prompt. Now, for the tough part. You need to write a CBIOS, which at a minimum, has your terminal I/O routines and disk I/O routines. The terminal I/O is going to depend on what hardware you have. The simplest is using a connection to a serial terminal. More complex routines may be needed if what you have is a video-mapped display. The disk routines aren't too bad. One set of them simply passes the disk parameter block information to CP/M; the other entry points merely store the track and sector and unit and transfer address of what's to be read or written and then reads or writes it. Part of the CBIOS is also the cold boot loader, which loads the DOS part of CP/M. There are other useful features in the CBIOS, such as punch, printer, and reader I/O as well as IOBYTE redirection, but you can do those later. After you've done this, you need to put things together. You can use ASM or ZASM to generate a hex file and LOAD to produce an image of what you want, then concatenate (using COPY) the boot sector, CBIOS and CP/M files into an image file of what's to be written to disk. You can then use the format funciton of 22DISK to create a new system disk, then drop PIP, ED, ASM, LOAD, DDT and whatever else you need onto it. Peruse the "CP/M System Alteration Guide" for examples of how to build a CBIOS and a boot loader. Hope this helps. Cheers, Chuck