Re: BOOT?

[pausch@saaf.se (Paul Schlyter)]

In article <QQ2%5.273$_q6.36346@news.uswest.net>,  <rtdos@qwest.net> wrote:
 
> Does anyone have any information on the Apple II/3 BOOT sectors and BOOT
> process?
 
The boot PROM and the boot sector is only 256 bytes each large.  Why
don't you disassemble them and trace the program flow within them?
Doing so requires some effort but will provide quite good insight
into what's happening.
 
Basically it works like this:
 
1. The PROM on the disk controller card can do two things: a) move
the arm on the disk out to the outermost track, and b) read the
first sector of that track to a fixed address ($300 or $800,
depending on whether it's a 13-sector or 16-sector boot PROM)
and then pass control to it.
 
2. The code in the 1st disk sector then reads in additional sectors
from the first track to some other fixed address.  This will read in
the RWTS plus code which calls the RWTS to read in the remainder
of the OS.
 
3. Finally the rest of the OS can be read in, and then control
is passed to the initialisation parts of the OS.
 
These steps are followed no matter what OS you're booting.  If
you run Apple CP/M for instance, the Z80 won't be started until
step 3. in the boot process is completed.
 
-- 
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