Re: Help with NIB, PO, and DO?

[Rubywand <rubywand@swbell.net>]

Charlie writes ...
> 
> "Jeffrey Theusch" <larva_jt1@yahoo.com> wrote in message
> 3b425c88.886497@news.wi.centurytel.net">news:3b425c88.886497@news.wi.centurytel.net...
> > On Mon, 2 Jul 2001 20:46:53 -0400, "Charlie"
> > >
> > >I would recommend that you get a copy of "Beneath Apple DOS" by Don Worth
> > >and Pieter Lechner.
> > >"Beneath Apple ProDOS" (same authors) is also recommended.
> > >These two books cover most of your questions in detail.
> >
> 
> > Do these books cover the low-level access of disk data?
> 
> Yes, "Beneath Apple DOS" in particular explains how to read a byte, load
> and write a byte, sense write protect switch, engage drive 1 or 2, turn the
> motor on/off, and use the stepper motor phases to move the head (relevant to
> understanding half and quarter tracks).  All without any operating system.
> You can't get much lower-level than that.
> It also explains how to use the RWTS routine to do low level I/O.  It
> explains sector skewing, nibble encoding, the controller card boot ROM, the
> memory DOS uses, the main internal routines, the file manager and a lot
> more.
> "Beneath Apple ProDOS" covers some of the same stuff but much of the book is
> about using ProDOS from assembly language.  Both books have chapters on
> customizing and disk protection schemes as well as short assembly language
> examples.
> 
> > I have wanted to obtain "Beneath Apple (pro)DOS" for some time, but I am
> > not into spending much money for these great references.
> 
> I (and I'm sure others here) will try to answer your questions but I
> wouldn't want to tackle a project like yours without these two books handy.
> 
 ....

     For sure, Beneath Apple DOS is one of the best two or three Apple II books
ever. There is one notable glitch which caused me all sorts of problems when I
first looked at sector ordering and tried translating DOS 3.3 sector naming to
ProDOS half-blocks. On page 3-23, the "DOS 3.3 Sector" listing is incorrect.

     Evidently, the writers misinterpreted the sector interleave table (which
usually resides at $BFB8-$BFC7 when DOS 3.3 is loaded).  The table is entered
with the DOS 3.3 sector name as the index to obtain the Physical Sector; not
the other way around.

     If you swap the header labels "Physical Sector" and "DOS 3.3 Sector" on
page 3-23, the listing is correct for DOS 3.3. (There's a good listing of 5.25"
Physical sectors, DOS 3.3 sectors, and ProDOS half-blocks on page 132 of the
Copy II Plus Version 9 manual.)



Rubywand