Date   : Wed, 30 Jun 2004 02:19:08 +0100 (BST)
From   : Greg Cook <debounce@...>
Subject: Re: bbcim/bbctape

On Sun, 27 Jun 2004 00:37:57 +0000 <40DE16E5.41C67EA6@...>
W.Scholten wrote:

> > Might I request a re-appearance of BBCIM, as I've found it
> indispensable
> > for opening up disc images and checking CRCs.
>
> Aha, I'm not the only one paranoid about file transfer ;)

True paranoia is sending the whole file twice.

> >  Possibly the file
> > whs_tape_utilities_10_5_2001.zip also.  If not, I'd be happy to host 
> them
> > both instead.
>
> Anyone can use/update/host those files. All files are under a BSD-like
> licence or public domain, so please do. 

Ta! Will post these on my next update.

> Btw, has anyone else noticed that the Atom uses half-1 bits at the end
> of a byte? This gives an awful mess decoding, 
[...]
> Hmm, I hope there aren't any custom
> produced bitstreams in games that do this, or the standard bitstream
> format is not adequate (probably not possible to make such tapes via the
> cassette output port on the BBC or is it?).

The new UEF spec supports single and half cycles when rendering what
it calls 'security waves', and at a pinch you could use that chunk for
this purpose.  There is also an ability to store tape data in fixed serial
formats - currently no extra cycles can be specified after the stop
bits, but this may change *ahem* in which case Atom output and any
protection schemes that do use it can be conveniently recorded.

Of course, when one's existing code wasn't designed with half bits in
mind, retrofitting can get very messy indeed...

As to generating Atom-style timings on the BBC, you would only need to
delay carefully each write to the ACIA, and it will synchronise to the
next 2400Hz cycle; notice that the inter-block gaps vary by one cycle
in length during a standard recording.

> If there are people willing to help debug/test/check or write code I'm
> more interested in updating/fixing. Sometimes it feels to me, as Mark
> Usher noted about his efforts on the BBC doc website, "What am I doing
> the effort for if there's very little help or feedback".

Me three.  Only one response to the Web site in 18 months, and without
the luxury of server logs, it's hard to know how many people are
affected by the quality of your code :S

Regards,

Greg

---

UEF format specification:
http://electrem.emuunlim.com/UEFSpecs.htm



       
       
               
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