From: Armin Vogl (Armin.Vogl_at_gmx.net)
Date: 2007-12-04 23:23:07
Hi Pete,
I read the infos on your page. I still have a few questions:
>We mentioned before that if the drive gets more than two '0' bits in a row,
>it clocks in a random '1' bit occasionally.
Is it really random ? I mean the 74LS193 is not reset by the BIT_SYNC line
in case there are more than two "0" in a row. Is it the variation in
rotation speed together with variation in the decoder clock which creates
different bytes for each rotation ? The decoder clock defines the "width" of
the bit in time and clocks the 74LS193. Would it be enough to have a number
of bits on the track that can not be divided by 8 to generate a pattern that
changes with each rotation ? This would still not be random, because after a
"1" bit is read, the byte that will be read only depends on how long you get
"0" bits. But this patternis not random. I think it would look like random
if the amount of bits on the track can not be divided by 8.
So the question is: does G64 support an amount of bits on a track rather
than bytes ?
I still don't get what is "weak" about the bits. I don't understand the term
"weak bit". It is not that the bits themselves are not stable on the
magnetic medium, but it is more that the drive electronics reads a different
byte for each rotation, or ?
Sorry if I ask questions that have already been answered elsewhere, but I
couldn't find a detailed explanation on the web.
Thanks
Armin
----- Original Message -----
From: "Pete Rittwage" <peter@rittwage.com>
To: <cbm-hackers@ling.gu.se>
Sent: Tuesday, December 04, 2007 10:49 PM
Subject: Re: Weak Bits
>> Hi !
>>
>> I would like to know more about weak bits. What are weak bits ? How can
>> they
>> be stored in the
>> GCR file format ? what would be necessary to support weak bits if you
>> want
>> to emulate the r/w
>> head for drive emulation ?
>
> There is a page on my site detailing most styles of copy protection used
> on the C64. Check under the "weak bits" section (but read the rest for
> background information)
>
> http://c64preservation.com/protection
>
> -
> Pete Rittwage
> C64 Preservation Project
> http://c64preservation.com
>
> Message was sent through the cbm-hackers mailing list
Message was sent through the cbm-hackers mailing list
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