[net.micro.amiga] Kickstart format

curtis@gitpyr.UUCP (Curtis Crowson) (02/27/86)

In article <8602251656.AA22138@cory> dillon@CORY.BERKELEY.EDU (Matt Dillon) writes:
>
>
>Aside: Can somebody tell me what the 'memory overlay' bit is on one of the
>I/O ports. It has something to do with the WCS, I think.  Also, I could
>not find any documentation on the format of the KickStart diskette, does 
>anybody have any information on that??
>
>				Thanks A lot,
>
>				-Matt


From experimentation with DiskEd, the 256K of data that is loaded into the
WCS from the Kickstart is read from sectors 1-512 on the Kickstart disk.
It is loaded as-is at $FC0000 (512 sectors * 512 bytes/sector = 256K).
Sector 0 contains 'KICK' followed by 508 zeros, the rest of the disk is
garbage except for the root block (880) which contains something to keep the
system happy if you stick the Kickstart in after booting up.

I *think* the boot sequence goes something like this:

   After being turned on or after <CTRL><A><A>, the boot ROM magically
   maps into low memory and begins execution.  If it finds the WCS empty,
   it asks for and reads in the Kickstart code.  Then it asks for the
   Workbench disk.  The first two sectors of the Workbench disk are read
   into memory at an arbitrary position (MUST be PC-relative code), and
   execution begins at location 12 of this code (the first three long
   words are as defined in "devices/bootblock.h").  This boot code either
   returns a failure code in D0 (producing a system alert), or null in
   D0 and a start address in A0.  It is expected to load more code off
   of the Workbench disk using a disk I/O request passed it in A1.
   Somewhere in all this confusion, the boot ROM fades away, never to
   be seen again.

The memory overlay bit either has to do with write protecting the WCS, or
possibly with switching the boot ROM in/out, anybody know??

Please!  Somebody at Commodore/Amiga correct me if I'm wrong (and by the
         way, is there any way to get at the boot ROM contents?).

Ken Beckett
Georgia Institute of Technology
uucp:..!{akgua,allegra,amd,hplabs,ihnp4,masscomp,ut-ngp}!gatech!gitpyr!curtis