'Vorpal (later) analysis'
Author:Lord Crass (guest: search)
Date: Fri, Mar 25th, 2011 @ 23:27 ( . )

I made a mistake in the commentary of that disassembly. In the Vorpal code, at $586-$58a, it reaches here if it read a $FF byte and branches if sync is NOT set. I originally had this the other way around (sync is set). This is due to the 1541 memory map I was using which has bit 7 of $1c00 listed as 0=data, 1=sync which is backwards. Perhaps the doc is referring to the voltage level on the actual pin instead of what the drive sees, since these are active-low.

Also, I originally wrote that the Maverick copier writes $FF $55 at the start of the track. It's actually $FF $FF $55. I missed the 2nd BVC which occurs at $099, which, absent another STA $1C01 will just write the previous byte again. So this does indeed write a 16 bit sync mark, which is how Maverick frames the track data properly. Note that the Vorpal loader doesn't look for this sync and will handle the data either way.


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Replies:
--* Vorpal (later) analysis
3/27/2011 @ 13:44--Pete Rittwage
3/27/2011 @ 15:31----Lord Crass
3/27/2011 @ 16:02------Pete Rittwage
3/28/2011 @ 00:01--------Lord Crass
3/28/2011 @ 21:25----------hyper active
4/02/2011 @ 01:53----------Lord Crass

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