On Sun, 15 Jan 2012, Vladimir Ivanov wrote:
Steve, I am not totally sure what you're after, but if I got your questions right: On Sat, 14 Jan 2012, Steve Nickolas wrote:Weeeeeeeeell... Of the first 3 tracks, here's usage for a DOS 3.3 48K slave: 0123456789ABCDEF 0##### ########## 1################ 2#####Is T0/S5 missing for a reason?Would it be possible to change usage to something more like this? 0123456789ABCDEF 0##### 1################ 2##### ##########Moving part of T0 to T2 is just a matter of loader for booting purposes. "INIT" would have to be rewritten, but it's screwed anyway since track #0 has to be written with non-standard format.As we already agreed to, "INIT" is prime sacrifice. ;-)
So it has to be done with a separate program. The tool wouldn't fit in INIT space anyway.
and then stuff two versions of the first 5 sectors onto the same track 0? (i.e., a 16-sector version and a 13-sector version).Ok, I guess you want to keep T1..T22 in 16-sector format, only T0 is funny.
I dunno if it'd work that way. Might have to be a 4-track 13-sector DOS.
Here's something even more easier to do and maintain:Put one 16-sector and one 13-sector S0 on T0. Fill the rest of the track with "macro" sectors encoded in 18-sector format, just as we discussed recently. The beauty of this approach is that the code in both S0 will be exactly the same for 13 and 16-sector cases - it will contain loader for the "macro" sectors from T0. In case 256 bytes aren't enough for such a loader (and you can't rely on the bootstrap ROM), revert to some simple scheme, even 4&4. But the layout of 18-sector "macro" sector is very easy and straightforward.Again, you write T0 in single pass.Now, the only problem with this scheme is that you want to have 16-sector format with 13-sector P5/P6 PROMs on the disk controller. Not reliable and you can't expect (I think) that users will have lucky combination of 16-sector sequencer PROM and 13-sector bootstrap PROM. (Consult Sather's "Understanding the Apple II" for details)
Which is why these disks usually run some form of DOS 3.2 (Bob Sander-Cederlof's assembler documentation for an early version actually mentioned using a 16/13 DOS 3.2.1), and one I've seen runs a form of 3.1.
So, to be on the safe side, you have to keep the whole disk in 13-sector format, and the "macro" portion of T0 to be in either something analogous to 18-sector format but with 5&1 encoding, or plain 4&4 for simplicity.
Yeah. -uso.