Re: Disk controller

["josephoswaldgg@hotmail.com" <josephoswald@gmail.com>]

simcop2387 wrote:
> Ok i've been playing around trying to get the disk controller to work
> (i've borrowed almost all (like 99.5%) of the code for it from the
> original java applelet emulator, and it seems that something is going
> wrong.
>
> thanks to the source to the disk rom i was able to verify that the
> emulated cpu is working properly (i could be wrong about that).
> what i don't know yet is why when it reaches the end of the rom it jumps
> to $0801 (which ends up filled with garbage it would appear when looking
> at the contents of the memory thanks to the apple monitor).  I'm tempted

The 16-sector disk controller ROM contains a boot routine which reads a
number of sectors from the disk into memory starting at address $800.
Then, it jumps to $801 to continue the boot process, assuming that
those sector(s) contained code to load the rest of the operating
system.

If there is garbage at $800... it is because either your disk (image)
is screwed up, or the controller did not see accurate data in the read
register.

The boot process for DOS 3.3 is described in Beneath Apple DOS, and for
ProDOS in Beneath Apple ProDOS (for which scanned copies exist online).