Nand Compare 1.1

nand compare (v1.1): (see end of file for version history)
--------------------

i made 6 reads of my nand with no matches (one of them was good but of course i
didn't know that at the time), but diffing them i could see that the differences
where spread all throughout the file, so i wrote this tool to reconstruct it

then i also discovered the usefulness of the compare function in verification of
the write, so hopefully this tool will be of use to other people


the tool has two functions:
---------------------------

- compare 2 nand images
better than simply using md5 as it tells you which blocks are mismatched, which
allows you to reread only those that are in error rather than the entire chip
(speeding up the process)

one use of this is when verifying a write by reading back the nand and comparing
it against the original you wrote, if you get a bad block just reread that
individual block, patch it into the full read and compare again (files are
reread each time you click compare, no need to reselect the same files in the
gui)

e.g. nandpro lpt: -w16 XBR.bin (write image as normal)
nandpro lpt: -r16 verify.bin (read back image)
(do comparison, shows block 2e mismatches)
nandpro lpt: -r16 2e.bin 2e 1 (read block 2e)
nandpro verify.bin: -w16 2e.bin 2e 1 (patch this new read into verify image)
(do comparison again, if still bad rewrite just this block and read it back again as above)


- reconstruct image from 3 bad reads
assumes that read errors don't occur in same place each time, which is true for
some read errors (e.g. lpt timing problems), if there is a good reason why you
can't read something then this may not be true

this tool cannot recreate a nand out of nothing, if you give it 3 files full of
zeros you'll get a recreated nand full of zeros, always look at a dump to make
sure it looks correct (e.g. has a microsoft copyright at the top, once you've
reconstructed a nand open it in 360 flash tool and make sure it reads ok there)

the tool works by comparing blocks between the 3 files, any block found matching
in 2 (or 3) of the files will be considered good, you will be warned if not all
blocks can be recovered, in which case you'll need to get more reads or look for
a good reason why your reads are so bad


version history:
----------------
1.1 (2009/12/13) - support for 512mb nand (assumes same block size as 16mb)
1.0 (2009/12/12) - first release