On Tue, Apr 07, 2009 at 03:43:49PM +0200, Rhialto wrote:
> On Mon 06 Apr 2009 at 08:34:59 -0500, Jim Brain wrote:
> > There were a document on the C64 Tape preservation project site, but  
> > they waved their hand over the CBM stock routines, stating they were  
> > more complex than many tape loaders and then they went on to describe  
> > how tape loaders for games work.
> 
> I remmember trying in the past to understand the standard tape reading
> routines. The tape writing routines were not too difficult, but the
> reading routines were quite different.

I tried to understand the tape routines in the KERNAL, but gave up.
Instead, I started by writing C2N232 firmware for sampling pulse widths
from the CASS WRITE line.  This is roughly the same as generating a .tap
file.  Then I wrote a decoder and finally encoder and a playback program.
The C2N232 firmware is somewhat hairy as well, but that is because it is
packed with so many features and it is entirely interrupt-driven.

> So if you're looking at the details of the tape format, start with the
> writing code and don't be surprised if the reading code is somewhat
> incomprehensible. All annotated ROM listings I've seen are really really
> skimpy on the details there as well!

My advice is: steer clear from the code, but sample the format first.
If all you have is the read routines and some data to feed them with,
then you could tweak the data and see what happens.  In an emulator,
that's too easy. :-)

	Marko

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