Disc reader project -- quick status update

[Keith 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