Re: Poor-man's Catweasel

[mwillegal <mike@willegal.net>]

HI Michael,

I'm a bit concerned about immediately starting the data after the
header because it appears that the RWTS code takes over 100
microseconds between reading the  address header, before starting a
sector data read or write.  That would equal to about 3 character
times on the disk.  This may not leave enough time to get the "IWM"
back in sync for the data read, since a large part of the 5 byte data
sync leader would have already passed by, if there was no gap.  Keep
in mind that the AVR I'm using is approximately 20 times faster than
the Apple ][, so I could essentially remove the entire gap, if I
pleased.   I'm a bit puzzled how the normal read function can read a
raw formatted sector reliably, given the fact that the format
function, greatly compresses this gap, compared to the write and read
sector functions.

I haven't had time to figure out the clobbered sector 1 problem, but
since there is no difference in gaps between various sectors (except
last to first),   I'm thinking that there is a just an ordinary logic
bug at work here.

Thanks and regards,
Mike Willegal

On Feb 6, 4:30 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> mwillegal wrote:
> > I'm pretty far along on a "smart" version for DIsk ][ drives,
> > formatted in DOS 3.3 format.
> >http://www.willegal.net/appleii/appleii-disk-int.htm.
>
> > Note that properly formatting a disk and/or writing to individual
> > sectors on a disk demands knowing and decoding the disk format on the
> > fly.
>
> Mike, on your web page you wrote:
>
>  >There is one final thing I need to do before actually testing out
>  >this write sector function.  That is to study the precise spacing
>  >between the end of the sector header and the sector data in Apple's
>  >RWTS.  I'll adjust my code to match as closely as possible.
>
> and:
>
>  >[I] have found that 2nd sector on a track can't be found after writing
>  >sector 0 data. There is some special handling of sector zero in Apple's
>  >RWTS format function.   I'm in process of figuring out how that affects
>  >the sector 0 to sector 1 spacing.
>
> When writing a sector, writing of sync nibbles should begin as soon as
> the epilog of the address is complete.  (In fact, the second epilog
> nibble is clobbered because of too little delay during formatting.)
>
> So allow enough time to read the clobbered nibble, then start writing
> several (6-8?) sync nibbles before the data header.
>
> The object is to keep the data as close as possible to the address
> field so that it doesn't overwrite too many sync nibbles leading into
> the next address field--which is what I think is clobbering the next
> sector after a write to sector 0.
>
> -michael
>
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