9 Dec
2009
9 Dec
'09
5:53 a.m.
Eric Smith wrote:
The data separator has to deal with a lot more than
just the variation
in drive speed. That variation has long-term and short-term components,
and it also has to deal with the bit shifting that isn't completely
avoided by write precompensation.
Can you put some rough ballpark numbers on how much total (worst case)
shifting you are talking about, altogether? I'm assuming the shift
would show up as distance/time between pulses, right?
For many disks you can read adequately using the very
simple software
data separator techniques that have been described previously in this
thread. However, for disks that are marginal in one way or another, the
simple techniques will fail.
So you are saying that the shift could be enough, for example, to make
two pulses that were written 4us apart appear as if they are 6us apart?
One of the advantages of sampling the pulses from the
drive and saving
the samples or delta times is that you can use data separation
algorithms that would be impractical in a real floppy disk system.
I think having access to the most raw form of the data possible is the
best idea too.
Any good book references for data separation algorithms? Would this
topic be covered in detail, for instance, in some other generic
engineering type reference, or ... ?
Thanks for any help....
Keith