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+---- Thread: C64 disk image FTP or search of .scp images (/showthread.php?tid=99)
RE: C64 disk image FTP or search of .scp images - jupp - 03-05-2014
correct data as part of the writing process? without knowing if the data read from the disk was ok? how does that work, magic?
RE: C64 disk image FTP or search of .scp images - admin - 03-05-2014
Yes, that is correct. You can determine if the flux level data is valid or not knowing the base format (MFM, FM, or GCR). You can call it magic if you like. I call it a very simple DSP routine. I am working on a new routine that makes it much smarter and can correct inconsistent data.
RE: C64 disk image FTP or search of .scp images - jupp - 03-06-2014
if it is so simple, i wonder why they didnt build it into their floppy controllers... *shrug*
also, what if the flux data is incorrect, yet valid?
RE: C64 disk image FTP or search of .scp images - Feltzkrone - 03-06-2014
Then you have valid data in the image and on the backup also. It's really as simple as that.
RE: C64 disk image FTP or search of .scp images - admin - 03-06-2014
Although it possible to have flux data appear within the normal bit cell timing, I have never seen a case where the adjacent bits are not skewed as too long or two short. This is how a write splice is detected.
RE: C64 disk image FTP or search of .scp images - jupp - 03-07-2014
Quote:Then you have valid data in the image and on the backup also. It's really as simple as that.but only because it is valid MFM/GCR/FM/whatever it is in no way guaranteed that it is the correct data. the only way to find that out is to decode it and compare against known good data. or to word it in a different way: if the GCR is invalid, then you know that it is incorrect data. but the other way around is not guaranteed.
RE: C64 disk image FTP or search of .scp images - admin - 03-07-2014
People are not thinking in the terms of flux, which allows the possibility of using processing algorithms on the flux data to determine validity without any type decoding to GCR/MFM or Hex data being required. Comparing versions or differences between two disks does require that you decode the data, but that is not required to determine the validity of the flux data.
RE: C64 disk image FTP or search of .scp images - jupp - 03-09-2014
only because you keep repeating it it wont get true. replace GCR by "flux" in the above sentence if you prefer that. (actually its even easier to have valid flux transitions that represent incorrect data)
RE: C64 disk image FTP or search of .scp images - admin - 03-09-2014
That's simply not the case. If it were, SCP would not work at all.