Re: Sunraycer Question

["Michael J. Mahon" <mjmahon@aol.com>]

Bryan Parkoff wrote:
>     I know the fact that Sunraycer will not run in any Apple II emulator 
> unless track $19, sector $0A, address: $17 is modified from $E7 to $F7 
> before it will run fine on any Apple II Emulator.
>     They state that it requires to have real Apple II hardware for rotating 
> disk timing which it is always unimplemented.  Is there a possibility that 
> we should implement rotating disk timing so Sunraycer will work on one Apple 
> II emulator without modifying Sunraycer's disk image?
>     Is there a way that Copy II Plus can measure Disk II speed correctly 
> which it should be at 200.1 ms instead of going up to 220 ms or greater 
> unless we implement the rotating disk timing properly?
>     Any suggestion is welcome.  I appreciate this.

Thomas Lai, who did the original modification, has looked further
into the incompatibility with emulators and has found that it is
a result of the "residue" of a disk copy protection method left
on the disk after deprotection that was "sufficient" to allow it
to run on a real Apple II.

The residue in this case is a nibble count routine that does not
exit until it finds a particular disk nibble in its scan.  The
original deprotector simply disabled the equality check on the
nibble count, but did not remove the counting code.

The best solution in such cases would be to remove completely
the copy protection, so that it is not an issue.  Since this
may be onerous or beyond the capabilities of some who just want
to play the game, it would be sufficient for an emulator to
simply return an 8-bit counter value whenever the disk read
register is accessed, since that will lead virtually any nibble
scan routine to exit promptly.

-michael

8-voice music synthesizer using NadaNet networking!
Home page:  http://members.aol.com/MJMahon/